Download The nervous system

The Brain or Encephalon
General Considerations and Divisions.—The brain, is contained within the cranium, and constitutes the upper,
greatly expanded part of the central nervous system. In its early embryonic condition it consists of three hollow vesicles,
termed the hind-brain or rhombencephalon, the mid-brain or mesencephalon, and the fore-brain or prosencephalon;
and the parts derived from each of these can be recognized in the adult Thus in the process of development the wall of the
hind-brain undergoes modification to form the medulla oblongata, the pons, and cerebellum, while its cavity is expanded to
form the fourth ventricle. The mid-brain forms only a small part of the adult brain; its cavity becomes the cerebral aqueduct (aqueduct of Sylvius), which serves as a tubular communication between the third and fourth ventricles; while its
walls are thickened to form the corpora quadrigemina and cerebral peduncles. The fore-brain undergoes great modification:
its anterior part or telencephalon expands laterally in the form of two hollow vesicles, the cavities of which become the
lateral ventricles, while the surrounding walls form the cerebral hemispheres and their commissures; the cavity of the posterior part or diencephalon forms the greater part of the third ventricle, and from its walls are developed most of the structures which bound that cavity.
The Medulla Oblongata (spinal bulb).—The medulla oblongata extends from the lower margin of the pons to a
plane passing transversely below the pyramidal decussation and above the first pair of cervical nerves; this plane corresponds with the upper border of the atlas behind, and the middle of the odontoid process of the axis in front; at this level the
medulla oblongata is continuous with the medulla spinalis. Its anterior surface is separated from the basilar part of the occipital bone and the upper part of the odontoid process by the membranes of the brain and the occipitoaxial ligaments. Its
posterior surface is received into the fossa between the hemispheres of the cerebellum, and the upper portion of it forms the
lower part of the floor of the fourth ventricle.
The medulla oblongata is pyramidal in shape, its broad extremity being directed upward toward the pons, while its
narrow, lower end is continuous with the medulla spinalis. It measures about 3 cm. in length, about 2 cm. in breadth at its
widest part, and about 1.25 cm. in thickness. The central canal of the medulla spinalis is prolonged into its lower half, and
then opens into the cavity of the fourth ventricle; the medulla oblongata may therefore be divided into a lower closed part
containing the central canal, and an upper open part corresponding with the lower portion of the fourth ventricle.
The Anterior Median Fissure (fissura mediana anterior; ventral or ventromedian fissure) contains a fold of pia
mater, and extends along the entire length of the medulla oblongata: it ends at the lower border of the pons in a small triangular expansion, termed the foramen cecum. Its lower part is interrupted by bundles of fibers which cross obliquely from
one side to the other, and constitute the pyramidal decussation. Some fibers, termed the anterior external arcuate fibers,
emerge from the fissure above this decussation and curve lateralward and upward over the surface of the medulla oblongata
to join the inferior peduncle.
The Posterior Median Fissure (fissura mediana posterior; dorsal or dorsomedian fissure) is a narrow groove; and
exists only in the closed part of the medulla oblongata; it becomes gradually shallower from below upward, and finally
ends about the middle of the medulla oblongata, where the central canal expands into the cavity of the fourth ventricle.
These two fissures divide the closed part of the medulla oblongata into symmetrical halves, each presenting elongated eminences which, on surface view, are continuous with the funiculi of the medulla spinalis. In the open part the halves
are separated by the anterior median fissure, and by a median raphé which extends from the bottom of the fissure to the
floor of the fourth ventricle. Further, certain of the cranial nerves pass through the substance of the medulla oblongata, and
are attached to its surface in series with the roots of the spinal nerves; thus, the fibers of the hypoglossal nerve represent the
upward continuation of the anterior nerve roots, and emerge in linear series from a furrow termed the antero-lateral sulcus. Similarly, the accessory, vagus, and glossopharyngeal nerves correspond with the posterior nerve roots, and are attached to the bottom of a sulcus named the postero-lateral sulcus. Advantage is taken of this arrangement to subdivide
each half of the medulla oblongata into three districts, anterior, middle, and posterior. Although these three districts appear to be directly continuous with the corresponding funiculi of the medulla spinalis, they do not necessarily contain the
same fibers, since some of the fasciculi of the medulla spinalis end in the medulla oblongata, while others alter their course
in passing through it.
The anterior district is named the pyramid (pyramis medullae oblongatae) and lies between the anterior median
fissure and the antero-lateral sulcus. Its upper end is slightly constricted, and between it and the pons the fibers of the abducent nerve emerge; a little below the pons it becomes enlarged and prominent, and finally tapers into the anterior funiculus of the medulla spinalis, with which, at first sight, it appears to be directly continuous.
The two pyramids contain the motor fibers which pass from the brain to the medulla oblongata and medulla spinalis,
corticobulbar and corticospinal fibers. When these pyramidal fibers are traced downward it is found that some two-thirds or
more of them leave the pyramids in successive bundles, and decussate in the anterior median fissure, forming what is
termed the pyramidal decussation. Having crossed the middle line, they pass down in the posterior part of the lateral funiculus as the lateral cerebrospinal fasciculus. The remaining fibers—i e., those which occupy the lateral part of the pyramid—do not cross the middle line, but are carried downward as the anterior cerebrospinal fasciculus into the anterior funiculus of the same side.
The greater part of the anterior proper fasciculus of the medulla spinalis is continued upward through the medulla
oblongata under the name of the medial longitudinal fasciculus.
The lateral district is limited in front by the antero-lateral sulcus and the roots of the hypoglossal nerve, and behind
by the postero-lateral sulcus and the roots of the accessory, vagus, and glossopharyngeal nerves. Its upper part consists of a
prominent oval mass which is named the olive, while its lower part is of the same width as the lateral funiculus of the medulla spinalis, and appears on the surface to be a direct continuation of it. As a matter of fact, only a portion of the lateral
funiculus is continued upward into this district, for the lateral cerebrospinal fasciculus passes into the pyramid of the oppo-
site side, and the dorsal spinocerebellar fasciculus is carried into the inferior peduncle in the posterior district. The ventral
spinocerebellar fasciculus is continued upward on the lateral surface of the medulla oblongata in the same relative position
it occupies in the spinal cord until it passes under cover of the external arcuate fibers. It passes beneath these fibers just
dorsal to the olive and ventral to the roots of the vagus and glossopharyngeal nerves; it continues upward through the pons
along the dorso-lateral edge of the lateral lemniscus. The remainder of the lateral funiculus consists chiefly of the lateral
proper fasciculus. Most of these fibers dip beneath the olive and disappear from the surface; but a small strand remains superficial to the olive. In a depression at the upper end of this strand is the acoustic nerve.
The olive (oliva; olivary body) is situated lateral to the pyramid, from which it is separated by the antero-lateral sulcus, and the fibers of the hypoglossal nerve. Behind, it is separated from the postero-lateral sulcus by the ventral spinocerebellar fasciculus. In the depression between the upper end of the olive and the pons lies the acoustic nerve. It measures
about 1.25 cm. in length, and between its upper end and the pons there is a slight depression to which the roots of the facial
nerve are attached. The external arcuate fibers wind across the lower part of the pyramid and olive and enter the inferior
peduncle.
The posterior district lies behind the postero-lateral sulcus and the roots of the accessory, vagus, and the glossopharyngeal nerves, and, like the lateral district, is divisible into a lower and an upper portion.
The lower part is limited behind by the posterior median fissure, and consists of the fasciculus gracilis and the fasciculus cuneatus. The fasciculus gracilis is placed parallel to and along the side of the posterior median fissure, and separated from the fasciculus cuneatus by the postero-intermediate sulcus and septum. The gracile and cuneate fasciculi are at
first vertical in direction; but at the lower part of the rhomboid fossa they diverge from the middle line in a V-shaped manner, and each presents an elongated swelling. That on the fasciculus gracilis is named the clava, and is produced by a subjacent nucleus of gray matter, the nucleus gracilis; that on the fasciculus cuneatus is termed the cuneate tubercle, and is
likewise caused by a gray nucleus, named the nucleus cuneatus. The fibers of these fasciculi terminate by arborizing
around the cells in their respective nuclei. A third elevation, produced by the substantia gelatinosa of Rolando, is present in
the lower part of the posterior district of the medulla oblongata. It lies on the lateral aspect of the fasciculus cuneatus, and is
separated from the surface of the medulla oblongata by a band of nerve fibers which form the spinal tract (spinal root) of
the trigeminal nerve. Narrow below, this elevation gradually expands above, and ends, about 1.25 cm. below the pons, in a
tubercle, the tubercle of Rolando (tuber cinereum).
The upper part of the posterior district of the medulla oblongata is occupied by the inferior peduncle, a thick ropelike strand situated between the lower part of the fourth ventricle and the roots of the glossopharyngeal and vagus nerves.
The inferior peduncles connect the medulla spinalis and medulla oblongata with the cerebellum, and are sometimes named
the restiform bodies. As they pass upward, they diverge from each other, and assist in forming the lower part of the lateral
boundaries of the fourth ventricle; higher up, they are directed backward, each passing to the corresponding cerebellar hemisphere. Near their entrance, into the cerebellum they are crossed by several strands of fibers, which run to the median sulcus of the rhomboid fossa, and are named the striae medullares. The inferior peduncle appears to be the upward continuation of the fasciculus gracilis and fasciculus cuneatus; this, however, is not so, as the fibers of these fasciculi end in the
gracile and cuneate nuclei. The constitution of the inferior peduncle will be subsequently discussed.
Caudal to the striae medullares the inferior peduncle is partly covered by the corpus pontobulbare, a thin mass of
cells and fibers extending from the pons between the origin of the VII and VIII cranial nerves.
Internal Structure of the Medulla Oblongata.—Although the external form of the medulla oblongata bears a certain resemblance to that of the upper part of the medulla spinalis, its internal structure differs widely from that of the latter,
and this for the following principal reasons: (1) certain fasciculi which extend from the medulla spinalis to the brain, and
vice versa, undergo a rearrangement in their passage through the medulla oblongata; (2) others which exist in the medulla
spinalis end in the medulla oblongata; (3) new fasciculi originate in the gray substance of the medulla oblongata and pass to
different parts of the brain; (4) the gray substance, which in the medulla spinalis forms a continuous H-shaped column, becomes greatly modified and subdivided in the medulla oblongata, where also new masses of gray substance are added; (5)
on account of the opening out of the central canal of the medulla spinalis, certain parts of the gray substance, which in the
medulla spinalis were more or less centrally situated, are displayed in the rhomboid fossa; (6) the medulla oblongata is intimately associated with many of the cranial nerves, some arising form, and others ending in, nuclei within its substance.
The Cerebrospinal Fasciculi.—The downward course of these fasciculi from the pyramids of the medulla oblongata and their partial decussation have already been described. In crossing to reach the lateral funiculus of the opposite side,
the fibers of the lateral cerebrospinal fasciculi extend backward through the anterior columns, and separate the head of each
of these columns from its base. The base retains its position in relation to the ventral aspect of the central canal, and, when
the latter opens into the fourth ventricle, appears in the rhomboid fossa close to the middle line, where it forms the nuclei of
the hypoglossal and abducent nerves; while above the level of the ventricle it exists as the nuclei of the trochlear and oculomotor nerves in relation to the floor of the cerebral aqueduct. The head of the column is pushed lateralward and forms the
nucleus ambiguus, which gives origin from below upward to the cranial part of the accessory and the motor fibers of the
vagus and glossopharyngeal, and still higher to the motor fibers of the facial and trigeminal nerves.
The fasciculus gracilis and fasciculus cuneatus constitute the posterior sensory fasciculi of the medulla spinalis;
they are prolonged upward into the lower part of the medulla oblongata, where they end respectively in the nucleus gracilis
and nucleus cuneatus. These two nuclei are continuous with the central gray substance of the medulla spinalis, and may be
regarded as dorsal projections of this, each being covered superficially by the fibers of the corresponding fasciculus. On
transverse section the nucleus gracilis appears as a single, more or less quadrangular mass, while the nucleus cuneatus consists of two parts: a larger, somewhat triangular, medial nucleus, composed of small or medium-sized cells, and a smaller
lateral nucleus containing large cells.
The fibers of the fasciculus gracilis and fasciculus cuneatus end by arborizing around the cells of these nuclei. From
the cells of the nuclei new fibers arise; some of these are continued as the posterior external arcuate fibers into the inferior
peduncle, and through it to the cerebellum, but most of them pass forward through the neck of the posterior column, thus
cutting off its head from its base. Curving forward, they decussate in the middle line with the corresponding fibers of the
opposite side, and run upward immediately behind the cerebrospinal fibers, as a flattened band, named the lemniscus or
fillet. The decussation of these sensory fibers is situated above that of the motor fibers, and is named the decussation of
the lemniscus or sensory decussation. The lemniscus is joined by the spinothalamic fasciculus, the fibers of which are
derived from the cells of the gray substance of the opposite side of the medulla spinalis.
The base of the posterior column at first lies on the dorsal aspect of the central canal, but when the latter opens into
the fourth ventricle, it appears in the lateral part of the rhomboid fossa. It forms the terminal nuclei of the sensory fibers of
the vagus and glossopharyngeal nerves, and is associated with the vestibular part of the acoustic nerve and the sensory root
of the facial nerve. Still higher, it forms a mass of pigmented cells—the locus caeruleus—in which some of the sensory
fibers of the trigeminal nerve appear to end. The head of the posterior column forms a long nucleus, in which the fibers of
the spinal tract of the trigeminal nerve largely end.
The dorsal spinocerebellar fasciculus (fasciculus cerebellospinalis; direct cerebellar tract) leaves the lateral district of the medulla oblongata; most of its fibers are carried backward into the inferior peduncle of the same side, and
through it are conveyed to the cerebellum; but some run upward with the fibers of the lemniscus, and, reaching the inferior
colliculus, undergo decussation, and are carried to the cerebellum through the superior peduncle.
The proper fasciculi (basis bundles) of the anterior and lateral funiculi largely consist of intersegmental fibers,
which link together the different segments of the medulla spinalis; they assist in the production of the formatio reticularis of
the medulla oblongata, and many of them are accumulated into a fasciculus which runs up close to the median raphé between the lemniscus and the rhomboid fossa; this strand is named the medial longitudinal fasciculus, and will be again
referred to.
Gray Substance of the Medulla Oblongata.—In addition to the gracile and cuneate nuclei, there are several other
nuclei to be considered. Some of these are traceable from the gray substance of the medulla spinalis, while others are unrepresented in it.
1. The hypoglossal nucleus is derived from the base of the anterior column; in the lower closed part of the medulla
oblongata it is situated on the ventrolateral aspect of the central canal; but in the upper part it approaches the rhomboid fossa, where it lies close to the middle line, under an eminence named the trigonum hypoglossi. Numerous fibers connect the
two nuclei, both nuclei send long dendrons across the midline to the opposite nucleus; commissure fibers also connect
them. The nucleus measures about 2 cm. in length, and consists of large multipolar nerve cells, similar to those in the anterior column of the spinal cord, whose axons constitute the roots of the hypoglossal nerve. These nerve roots leave the ventral side of the nucleus, pass forward between the white reticular formation and the gray reticular formation, some between
the inferior olivary nucleus and the medial accessory olivary nucleus, and emerge from the antero-lateral sulcus.
2. The nucleus ambiguus, the somatic motor nucleus of the glossopharyngeal, vagus and cranial portion of the accessory nerves, is the continuation into the medulla oblongata of the dorso-lateral cell group of the anterior column of the
spinal cord. Its large multipolar cells are like those in the anterior column of the cord; they form a slender column in the
deep part of the formatio reticularis grisea about midway between the dorsal accessory olive and the nucleus of the spinal
tract of the trigeminal. It extends from the level of the decussation of the median fillet to the upper end of the medulla oblongata. Its fibers first pass backward toward the floor of the fourth ventricle and then curve rather abruptly lateralward and
ventrally to join the fibers from the dorsal nucleus.
3. The dorsal nucleus, nucleus ala cinerea, often called the sensory nucleus or the terminal nucleus of the sensory
fibers of the glossopharyngeal and vagus nerves, is probably a mixed nucleus and contains not only the terminations of the
sympathetic afferent or sensory fibers and the cells connected with them but contains also cells which give rise to sympathetic efferent or preganglionic fibers. These preganglionic fibers terminate in sympathetic ganglia from which the impulses
are carried by other neurons. The cells of the dorsal nucleus are spindle-shaped, like those of the posterior column of the
spinal cord, and the nucleus is usually considered as representing the base of the posterior column. It measures about 2 cm.
in length, and in the lower, closed part of the medulla oblongata is situated behind the hypoglossal nucleus; whereas in the
upper, open part it lies lateral to that nucleus, and corresponds to an eminence, named the ala cinerea (trigonum vagi), in
the rhomboid fossa.
5. The olivary nuclei are three in number on either side of the middle line, viz., the inferior olivary nucleus, and the
medial and dorsal accessory olivary nuclei; they consist of small, round, yellowish cells and numerous fine nerve fibers. (a)
The inferior olivary nucleus is the largest, and is situated within the olive. It consists of a gray folded lamina arranged in
the form of an incomplete capsule, opening medially by an aperture called the hilum emerging from the hilum are numerous fibers which collectively constitute the peduncle of the olive. The axons, olivocerebellar fibers, which leave the olivary nucleus pass out through the hilum and decussate with those from the opposite olive in the raphé, then as internal arcuate fibers they pass partly through and partly around the opposite olive and enter the inferior peduncle to be distributed to
the cerebellar hemisphere of the opposite side from which they arise. The fibers are smaller than the internal arcuate fibers
connected with the median lemniscus. Fibers passing in the opposite direction from the cerebellum to the olivary nucleus
are often described but their existence is doubtful. Much uncertainty also exists in regard to the connections of the olive and
the spinal cord. Important connections between the cerebrum and the olive of the same side exist but the exact pathway is
unknown. Many collaterals from the reticular formation and from the pyramids enter the inferior olivary nucleus. Removal
of one cerebellar hemisphere is followed by atrophy of the opposite olivary nucleus. (b) The medial accessory olivary
nucleus lies between the inferior olivary nucleus and the pyramid, and forms a curved lamina, the concavity of which is
directed laterally. The fibers of the hypoglossal nerve, as they traverse the medulla, pass between the medial accessory and
the inferior olivary nuclei. (c) The dorsal accessory olivary nucleus is the smallest, and appears on transverse section as a
curved lamina behind the inferior olivary nucleus.
6. The nucleus arcuatus is described below with the anterior external arcuate fibers.
Inferior Peduncle (restiform body).—The position of the inferior peduncles has already been described. Each comprises:
(1) Fibers from the dorsal spinocerebellar fasciculus, which ascends from the lateral funiculus of the medulla spinalis.
(2) The olivocerebellar fibers from the opposite olivary nucleus.
(3) Internal arcuate fibers from the gracile and cuneate nuclei of the opposite side; these fibers form the deeper
and larger part of the inferior peduncle.
(4) The anterior external arcuate fibers vary as to their prominence in different cases: in some they form an almost continuous layer covering the pyramid and olive, while in others they are barely visible on the surface. They arise
from the cells of the gracile and cuneate nuclei, and passing forward through the formatio reticularis, decussate in the middle line. Most of them reach the surface by way of the anterior median fissure, and arch backward over the pyramid. Reinforced by others which emerge between the pyramid and olive, they pass backward over the olive and lateral district of the
medulla oblongata, and enter the inferior peduncle. They thus connect the cerebellum with the gracile and cuneate nuclei of
the opposite side. As the fibers arch across the pyramid, they enclose a small nucleus which lies in front of and medial to
the pyramid. This is named the nucleus arcuatus, and is serially continuous above with the nuclei pontis in the pons; it
contains small fusiform cells, around which some of the arcuate fibers end, and from which others arise.
(5) The posterior external arcuate fibers also take origin in the gracile and cuneate nuclei; they pass to the inferior
peduncle of the same side. It is uncertain whether fibers are continued directly from the gracile and cuneate fasciculi into
the inferior peduncle.
(6) Fibers from the terminal sensory nuclei of the cranial nerves, especially the vestibular. Some of the fibers of the
vestibular nerve are thought to continue directly into the cerebellum.
(7) Fibers from the ventral spinocerebellar fasciculus.
(8) The existence of fibers from the cerebellum (cerebellobulbar, cerebelloölivary, and cerebellospinal) to the medulla and spinal cord is very uncertain.
Formatio Reticularis.—This term is applied to the coarse reticulum which occupies the anterior and lateral districts
of the medulla oblongata. It is situated behind the pyramid and olive, extending laterally as far as the inferior peduncles,
and dorsally to within a short distance of the rhomboid fossa. The reticulum is caused by the intersection of bundles of fibers running at right angles to each other, some being longitudinal, others more or less transverse in direction. The formatio
reticularis presents a different appearance in the anterior district from what it does in the lateral; in the former, there is an
almost entire absence of nerve cells, and hence this part is known as the reticularis alba; whereas in the lateral district
nerve cells are numerous, and as a consequence it presents a gray appearance, and is termed the reticularis grisea.
In the substance of the formatio reticularis are two small nuclei of gray matter: one, the inferior central nucleus
(nucleus of Roller), near the dorsal aspect of the hilus of the inferior olivary nucleus; the other, the nucleus lateralis, between the olive and the spinal tract of the trigeminal nerve.
In the reticularis alba the longitudinal fibers form two well-defined fasciculi, viz.: (1) the lemniscus, which lies
close to the raphé, immediately behind the fibers of the pyramid; and (2) the medial longitudinal fasciculus, which is continued upward from the anterior and lateral proper fasciculi of the medulla spinalis, and, in the upper part of the medulla
oblongata, lies between the lemniscus and the gray substance of the rhomboid fossa. The longitudinal fibers in the reticularis grisea are derived from the lateral funiculus of the medulla spinalis after the lateral cerebrospinal fasciculus has passed
over to the opposite side, and the dorsal spinocerebellar fasciculus has entered the inferior peduncle. They form indeterminate fibers, with the exception of a bundle named the fasciculus solitarius, which is made up of descending fibers of the
vagus and glossopharyngeal nerves. The transverse fibers of the formatio reticularis are the arcuate fibers already described.
The Pons (pons Varoli).—The pons or forepart of the hind-brain is situated in front of the cerebellum. From its superior surface the cerebral peduncles emerge, one on either side of the middle line. Curving around each peduncle, close to
the upper surface of the pons, a thin white band, the taenia pontis, is frequently seen; it enters the cerebellum between the
middle and superior peduncles. Behind and below, the pons is continuous with the medulla oblongata, but is separated from
it in front by a furrow in which the abducent, facial, and acoustic nerves appear.
Its ventral or anterior surface (pars basilaris pontis) is very prominent, markedly convex from side to side, less so
from above downward. It consists of transverse fibers arched like a bridge across the middle line, and gathered on either
side into a compact mass which forms the middle peduncle. It rests upon the clivus of the sphenoidal bone, and is limited
above and below by well-defined borders. In the middle line is the sulcus basilaris for the lodgement of the basilar artery;
this sulcus is bounded on either side by an eminence caused by the descent of the cerebrospinal fibers through the substance
of the pons. Outside these eminences, near the upper border of the pons, the trigeminal nerves make their exit, each consisting of a smaller, medial, motor root, and a larger, lateral, sensory root; vertical lines drawn immediately beyond the trigeminal nerves, may be taken as the boundaries between the ventral surface of the pons and the middle cerebellar peduncle.
Its dorsal or posterior surface (pars dorsalis pontis), triangular in shape, is hidden by the cerebellum, and is
bounded laterally by the superior peduncle; it forms the upper part of the rhomboid fossa, with which it will be described.
Structure.—Transverse sections of the pons show it to be composed of two parts which differ in appearance and
structure: thus, the basilar or ventral portion consists for the most part of fibers arranged in transverse and longitudinal bun-
dles, together with a small amount of gray substance; while the dorsal tegmental portion is a continuation of the reticular
formation of the medulla oblongata, and most of its constituents are continued into the tegmenta of the cerebral peduncles.
The basilar part of the pons consists of—(a) superficial and deep transverse fibers, (b) longitudinal fasciculi, and
(c) some small nuclei of gray substance, termed the nuclei pontis which give rise to the transverse fibers.
The superficial transverse fibers (fibrae pontis superficiales) constitute a rather thick layer on the ventral surface
of the pons, and are collected into a large rounded bundle on either side of the middle line. This bundle, with the addition of
some transverse fibers from the deeper part of the pons, forms the greater part of the brachium pontis.
The deep transverse fibers (fibrae pontis profundae) partly intersect and partly lie on the dorsal aspect of the cerebrospinal fibers. They course to the lateral border of the pons, and form part of the middle peduncle; the further connections
of this brachium will be discussed with the anatomy of the cerebellum.
The longitudinal fasciculi (fasciculi longitudinales) are derived from the cerebral peduncles, and enter the upper
surface of the pons. They stream downward on either side of the middle line in larger or smaller bundles, separated from
each other by the deep transverse fibers; these longitudinal bundles cause a forward projection of the superficial transverse
fibers, and thus give rise to the eminences on the anterior surface. Some of these fibers end in, or give off collateral to, the
nuclei pontis. An important pathway is thus formed between the cerebral cortex and the cerebellum, the first neuron having
its cell body in the cortex and sending its axon through the internal capsule and cerebral peduncle to form synapses either
by terminals or collaterals with cell bodies situated in the nuclei pontis. Axons from these cells form the transverse fibers
which pass through the middle peduncle into the cerebellum. Others after decussating, terminate either directly or indirectly
in the motor nuclei of the trigeminal, abducent, facial, and hypoglossal nerves; but most of them are carried through the
pons, and at its lower surface are collected into the pyramids of the medulla. The fibers which end in the motor nuclei of
the cranial nerves are derived from the cells of the cerebral cortex, and bear the same relation to the motor cells of the cranial nerves that the cerebrospinal fibers bear to the motor cells in the anterior column of the medulla spinalis. Probably
none of the collaterals or terminals of the cerebrospinal and cerebrobulbar fibers end directly in the motor nuclei of the spinal and cranial nerves, one or more association neurons are probably interpolated in the pathway.
The nuclei pontis are serially continuous with the arcuate nuclei in the medulla, and consist of small groups of multipolar nerve cells which are scattered between the bundles of transverse fibers.
The dorsal or tegmental part of the pons is chiefly composed of an upward continuation of the reticular formation
and gray substance of the medulla oblongata. It consists of transverse and longitudinal fibers and also contains important
gray nuclei, and is subdivided by a median raphé, which, however, does not extend into the basilar part, being obliterated
by the transverse fibers. The transverse fibers in the lower part of the pons are collected into a distinct strand, named the
trapezoid body. This consists of fibers which arise from the cells of the cochlear nucleus, and will be referred to in connection with the cochlear division of the acoustic nerve. In the substance of the trapezoid body is a collection of nerve cells,
which constitutes the trapezoid nucleus. The longitudinal fibers, which are continuous with those of the medulla oblongata, are mostly collected into two fasciculi on either side. One of these lies between the trapezoid body and the reticular formation, and forms the upward prolongation of the lemniscus; the second is situated near the floor of the fourth ventricle,
and is the medial longitudinal fasciculus. Other longitudinal fibers, more diffusely distributed, arise from the cells of the
gray substance of the pons.
The rest of the dorsal part of the pons is a continuation upward of the formatio reticularis of the medulla oblongata,
and, like it, presents the appearance of a network, in the meshes of which are numerous nerve cells. Besides these scattered
nerve cells, there are some larger masses of gray substance, viz., the superior olivary nucleus and the nuclei of the trigeminal, abducent, facial, and acoustic nerves.
1. The superior olivary nucleus (nucleus olivaris superior) is a small mass of gray substance situated on the dorsal
surface of the lateral part of the trapezoid body. Rudimentary in man, but well developed in certain animals, it exhibits the
same structure as the inferior olivary nucleus, and is situated immediately above it. Some of the fibers of the trapezoid body
end by arborizing around the cells of this nucleus, while others arise from these cells.
2. The nuclei of the trigeminal nerve (nuclei n. trigemini) in the pons are two in number: a motor and a sensory.
The motor nucleus is situated in the upper part of the pons, close to its posterior surface and along the line of the lateral
margin of the fourth ventricle. It is serially homologous with the nucleus ambiguus and the dorso-lateral cell group of the
anterior column of the spinal cord. The axis-cylinder processes of its cells form the motor root of the trigeminal nerve. The
mesencephalic root arises from the gray substance of the floor of the cerebral aqueduct, joins the motor root and probably
conveys fibers of muscle sense from the temporal, masseter and pterygoid muscles. It is not altogether clear whether the
mesencephalic root is motor or sensory. The sensory nucleus is lateral to the motor one, and beneath the superior peduncle.
Some of the sensory fibers of the trigeminal nerve end in this nucleus; but the greater number descend, under the name of
the spinal tract of the trigeminal nerve, to end in the substantia gelatinosa of Rolando. The roots, motor and sensory, of the
trigeminal nerve pass through the substance of the pons and emerge near the upper margin of its anterior surface.
3. The nucleus of the abducent nerve (nucleus n. abducentis) is a circular mass of gray substance situated close to
the floor of the fourth ventricle, above the striae medullares and subjacent to the medial eminence: it lies a little lateral to
the ascending part of the facial nerve. The fibers of the abducent nerve pass forward through the entire thickness of the
pons on the medial side of the superior olivary nucleus, and between the lateral fasciculi of the cerebrospinal fibers, and
emerge in the furrow between the lower border of the pons and the pyramid of the medulla oblongata.
4. The nucleus of the facial nerve (nucleus n. fascialis) is situated deeply in the reticular formation of the pons, on
the dorsal aspect of the superior olivary nucleus, and the roots of the nerve derived from it pursue a remarkably tortuous
course in the substance of the pons. At first they pass backward and medialward until they reach the rhomboid fossa, close
to the median sulcus, where they are collected into a round bundle; this passes upward and forward, producing an elevation,
the colliculus facialis, in the rhomboid fossa, and then takes a sharp bend, and arches lateralward through the substance of
the pons to emerge at its lower border in the interval between the olive and the inferior peduncle of the medulla oblongata.
5. The nucleus of the cochlear nerve consists of: (a) the lateral cochlear nucleus, corresponding to the tuberculum
acusticum on the dorso-lateral surface of the inferior peduncle; and (b) the ventral or accessory cochlear nucleus, placed
between the two divisions of the nerve, on the ventral aspect of the inferior peduncle.
The nuclei of the vestibular nerve. (a) The medial (dorsal or chief vestibular nucleus), corresponding to the lower part of the area acustica in the rhomboid fossa; the caudal end of this nucleus is sometimes termed the descending or
spinal vestibular nucleus. (b) The lateral or nucleus of Deiters, consisting of large cells and situated in the lateral angle
of the rhomboid fossa; the dorso-lateral part of this nucleus is sometimes termed the nucleus of Bechterew.
The fibers of the vestibular nerve enter the medulla oblongata on the medial side of those of the cochlear, and pass
between the inferior peduncle and the spinal tract of the trigeminal. They then divide into ascending and descending fibers.
The latter end by arborizing around the cells of the medial nucleus, which is situated in the area acustica of the rhomboid
fossa. The ascending fibers either end in the same manner or in the lateral nucleus, which is situated lateral to the area
acustica and farther from the ventricular floor. Some of the axons of the cells of the lateral nucleus, and possibly also of the
medial nucleus, are continued upward through the inferior peduncle to the roof nuclei of the opposite side of the cerebellum, to which also other fibers of the vestibular root are prolonged without interruption in the nuclei of the medulla oblongata. A second set of fibers from the medial and lateral nuclei end partly in the tegmentum, while the remainder ascend in
the medial longitudinal fasciculus to arborize around the cells of the nuclei of the oculomotor nerve.
The Cerebellum.—The cerebellum constitutes the largest part of the hindbrain. It lies behind the pons and medulla
oblongata; between its central portion and these structures is the cavity of the fourth ventricle. It rests on the inferior occipital fossae, while above it is the tentorium cerebelli, a fold of dura mater which separates it from the tentorial surface of the
cerebrum. It is somewhat oval in form, but constricted medially and flattened from above downward, its greatest diameter
being from side. Its surface is not convoluted like that of the cerebrum, but is traversed by numerous curved furrows or
sulci, which vary in depth at different parts, and separate the laminae of which it is composed. Its average weight in the
male is about 150 gms. In the adult the proportion between the cerebellum and cerebrum is about 1 to 8, in the infant about
1 to 20.
Lobes of the Cerebellum.—The cerebellum consists of three parts, a median and two lateral, which are continuous
with each other, and are substantially the same in structure. The median portion is constricted, and is called the vermis,
from its annulated appearance which it owes to the transverse ridges and furrows upon it; the lateral expanded portions are
named the hemispheres. On the upper surface of the cerebellum the vermis is elevated above the level of the hemispheres,
but on the under surface it is sunk almost out of sight in the bottom of a deep depression between them; this depression is
called the vallecula cerebelli, and lodges the posterior part of the medulla oblongata. The part of the vermis on the upper
surface of the cerebellum is named the superior vermis; that on the lower surface, the inferior vermis. The hemispheres
are separated below and behind by a deep notch, the posterior cerebellar notch, and in front by a broader shallower notch,
the anterior cerebellar notch. The anterior notch lies close to the pons and upper part of the medullas, and its superior
edge encircles the inferior colliculi and the superior cerebellar peduncle. The posterior notch contains the upper part of the
falx cerebelli, a fold of dura mater.
The cerebellum is characterized by a laminated or foliated appearance; it is marked by deep, somewhat curved fissures, which extend for a considerable distance into its substance, and divide it into a series of layers or leaves. The largest
and deepest fissure is named the horizontal sulcus. It commences in front of the pons, and passes horizontally around the
free margin of the hemisphere to the middle line behind, and divides the cerebellum into an upper and a lower portion. Several secondary but deep fissures separate the cerebellum into lobes, and these are further subdivided by shallower sulci,
which separate the individual folia or laminae from each other. Sections across the laminae show that the folia, though differing in appearance from the convolutions of the cerebrum, are analogous to them, inasmuch as they consist of central
white substance covered by gray substance.
The cerebellum is connected to the cerebrum, pons, and medulla oblongata; to the cerebrum by the superior peduncle, to the pons by the middle peduncle, and to the medulla oblongata by the inferior peduncles.
The upper surface of the cerebellum is elevated in the middle and sloped toward the circumference, the hemispheres being connected together by the superior vermis, which assumes the form of a raised median ridge, most prominent
in front, but not sharply defined from the hemispheres. The superior vermis is subdivided from before backward into the
lingula, the lobulus centralis, the monticulus and the folium vermis, and each of these, with the exception of the lingula, is
continuous with the corresponding parts of the hemispheres—the lobulus centralis with the alae, the monticulus with the
quadrangular lobules, and the folium vermis with the superior semilunar lobules.
The lingula (lingula cerebelli) is a small tongue-shaped process, consisting of four or five folia; it lies in front of the
lobulus centralis, and is concealed by it. Anteriorly, it rests on the dorsal surface of the anterior medullary velum, and its
white substance is continuous with that of the velum.
The Lobulus Centralis and Alae.—The lobulus centralis is a small square lobule, situated in the anterior cerebellar notch. It overlaps the lingula, from which it is separated by the precentral fissure; laterally, it extends along the upper
and anterior part of each hemisphere, where it forms a wing-like prolongation, the ala lobuli centralis.
The Monticulus and Quadrangular Lobules.—The monticulus is the largest part of the superior vermis. Anteriorly, it overlaps the lobulus centralis, from which it is separated by the postcentral fissure; laterally, it is continuous with the
quadrangular lobule in the hemispheres. It is divided by the preclival fissure into an anterior, raised part, the culmen or
summit, and a posterior sloped part, the clivus; the quadrangular lobule is similarly divided. The culmen and the anterior
parts of the quadrangular lobules form the lobus culminis; the clivus and the posterior parts, the lobus clivi.
The Folium Vermis and Superior Semilunar Lobule.—The folium vermis (folium cacuminis; cacuminal lobe) is
a short, narrow, concealed band at the posterior extremity of the vermis, consisting apparently of a single folium, but in
reality marked on its upper and under surfaces by secondary fissures. Laterally, it expands in either hemisphere into a considerable lobule, the superior semilunar lobule (lobulus semilunaris superior; postero-superior lobules), which occupies
the posterior third of the upper surface of the hemisphere, and is bounded below by the horizontal sulcus. The superior
semilunar lobules and the folium vermis form the lobus semilunaris.
The under surface of the cerebellum presents, in the middle line, the inferior vermis, buried in the vallecula, and
separated from the hemisphere on either side by a deep groove, the sulcus valleculae. Here, as on the upper surface, there
are deep fissures, dividing it into separate segments or lobules; but the arrangement is more complicated, and the relation of
the segments of the vermis to those of the hemispheres is less clearly marked. The inferior vermis is subdivided from before backward, into (1) the nodule, (2) the uvula, (3) the pyramid, and (4) the tuber vermis; the corresponding parts on
the hemispheres are (1) the flocculus, (2) the tonsilla cerebelli, (3) the biventral lobule, and (4) the inferior semilunar
lobule. The three main fissures are (1) the postnodular fissure, which runs transversely across the vermis, between the
nodule and the uvula. In the hemispheres this fissure passes in front of the tonsil, crosses between the flocculus in front and
the biventral lobule behind, and joins the anterior end of the horizontal sulcus. (2) The prepyramidal fissure crosses the
vermis between the uvula in front and the pyramid behind, then curves forward between the tonsil and the biventral lobe, to
join the postnodular fissure. (3) The postpyramidal fissure passes across the vermis between the pyramid and the tuber
vermis, and, in the hemispheres, courses behind the tonsil and biventral lobules, and then along the lateral border of the
biventral lobule to the postnodular sulcus; in the hemisphere it forms the anterior boundary of the inferior semilunar lobule.
The Nodule and Flocculus.—The nodule (nodulus vermis; nodular lobe), or anterior end of the inferior vermis,
abuts against the roof of the fourth ventricle, and can only be distinctly seen after the cerebellum has been separated from
the medulla oblongata and pons. On either side of the nodule is a thin layer of white substance, named the posterior medullary velum. It is semilunar in form, its convex border being continuous with the white substance of the cerebellum; it
extends on either side as far as the flocculus. The flocculus is a prominent, irregular lobule, situated in front of the biventral
lobule, between it and the middle cerebellar peduncle. It is subdivided into a few small laminae, and is connected to the
inferior medullary velum by its central white core. The flocculi, together with the posterior medullary velum and nodule,
constitute the lobus noduli.
The Uvula and Tonsilla.—The uvula (uvula vermis; uvular lobe) forms a considerable portion of the inferior vermis; it is separated on either side from the tonsil by the sulcus valleculae, at the bottom of which it is connected to the tonsil by a ridge of gray matter, indented on its surface by shallow furrows, and hence called the furrowed band. The tonsilla
(tonsilla cerebelli; amygdaline nucleus) is a rounded mass, situated in the hemispheres. Each lies in a deep fossa, termed
the bird’s nest (nidus avis), between the uvula and the biventral lobule. The uvula and tonsillae form the lobus uvulae.
The Pyramid and Biventral lobules constitute the lobus pyramidis. The pyramid is a conical projection, forming
the largest prominence of the inferior vermis. It is separated from the hemispheres by the sulcus valleculae, across which it
is connected to the biventral lobule by an indistinct gray band, analogous to the furrowed band already described. The
biventral lobule is triangular in shape; its apex points backward, and is joined by the gray band to the pyramid. The lateral
border is separated from the inferior semilunar lobule by the postpyramidal fissure. The base is directed forward, and is on
a line with the anterior border of the tonsil, and is separated from the flocculus by the postnodular fissure.
The Tuber Vermis (tuber valvulae) and the Inferior Semilunar Lobule (lobulus semilunaris inferior; posterosuperior lobule) collectively form the lobus tuberus (tuberae lobe). The tuber vermis, the most posterior division of the
inferior vermis, is of small size, and laterally spreads out into the large inferior semilunar lobules, which comprise at least
two-thirds of the inferior surface of the hemisphere.
Internal Structure of the Cerebellum.—The cerebellum consists of white and gray substance.
White Substance.—If a sagittal section be made through either hemisphere, the interior will be found to consist of a
central stem of white substance, in the middle of which is a gray mass, the dentate nucleus. From the surface of this central white stem a series of plates is prolonged; these are covered with gray substance and form the laminae. In consequence
of the main branches from the central stem dividing and subdividing, a characteristic appearance, named the arbor vitae, is
presented. If the sagittal section be made through the middle of the vermis, it will be found that the central stem divides into
a vertical and a horizontal branch. The vertical branch passes upward to the culmen monticuli, where it subdivides freely,
one of its ramifications passing forward and upward to the central lobule. The horizontal branch passes backward to the
folium vermis, greatly diminished in size in consequence of having given off large secondary branches; one, from its upper
surface, ascends to the clivus monticuli; the others descend, and enter the lobes in the inferior vermis, viz., the tuber vermis,
the pyramid, the uvula, and the nodule.
The white substance of the cerebellum includes two sets of nerve fibers: (1) projection fibers, (2) fibrae propriae.
Projection Fibers.—The cerebellum is connected to the other parts of the brain by three large bundles of projection
fibers, viz., to the cerebrum by the superior peduncle, to the pons by the middle peduncle, and to the medulla oblongata by
the inferior peduncles.
The superior cerebellar peduncles (brachia conjunctiva), two in number, emerge from the upper and medial part
of the white substance of the hemispheres and are placed under cover of the upper part of the cerebellum. They are joined
to each other across the middle line by the anterior medullary velum, and can be followed upward as far as the inferior colliculi, under which they disappear. Below, they form the upper lateral boundaries of the fourth ventricle, but as they ascend
they converge on the dorsal aspect of the ventricle and thus assist in roofing it in.
The fibers of the superior peduncle are mainly derived from the cells of the dentate nucleus of the cerebellum and
emerge from the hilus of this nucleus; a few arise from the cells of the smaller gray nuclei in the cerebellar white substance,
and others from the cells of the cerebellar cortex. They are continued upward beneath the corpora quadrigemina, and the
fibers of the two peduncles undergo a complete decussation ventral to the Sylvian aqueduct. Having crossed the middle line
they divide into ascending and descending groups of fibers, the former ending in the red nucleus, the thalamus, and the nucleus of the oculomotor nerve, while the descending fibers can be traced as far as the dorsal part of the pons; Cajal believes
them to be continued into the anterior funiculus of the medulla spinalis.
As already stated, the majority of the fibers of the ventral spinocerebellar fasciculus of the medulla spinalis pass to
the cerebellum, which they reach by way of the superior peduncle.
The middle cerebellar peduncles (brachia pontis) are composed entirely of centripetal fibers, which arise from the
cells of the nuclei pontis of the opposite side and end in the cerebellar cortex; the fibers are arranged in three fasciculi, superior, inferior, and deep. The superior fasciculus, the most superficial, is derived from the upper transverse fibers of the
pons; it is directed backward and lateralward superficial to the other two fasciculi, and is distributed mainly to the lobules
on the inferior surface of the cerebellar hemisphere and to the parts of the superior surface adjoining the posterior and lateral margins. The inferior fasciculus is formed by the lowest transverse fibers of the pons; it passes under cover of the
superior fasciculus and is continued downward and backward more or less parallel with it, to be distributed to the folia on
the under surface close to the vermis.
The deep fasciculus comprises most of the deep transverse fibers of the pons. It is at first covered by the superior
and inferior fasciculi, but crosses obliquely and appears on the medial side of the superior, from which it receives a bundle;
its fibers spread out and pass to the upper anterior cerebellar folia. The fibers of this fasciculus cover those of the restiform
body.
The inferior cerebellar peduncles (restiform bodies) pass at first upward and lateralward, forming part of the lateral walls of the fourth ventricle, and then bend abruptly backward to enter the cerebellum between the superior and middle
peduncles. Each contains the following fasciculi: (1) the dorsal spinocerebellar fasciculus of the medulla spinalis, which
ends mainly in the superior vermis; (2) fibers from the gracile and cuneate nuclei of the same and of the opposite sides; (3)
fibers from the opposite olivary nuclei; (4) crossed and uncrossed fibers from the reticular formation of the medulla oblongata; (5) vestibular fibers, derived partly from the vestibular division of the acoustic nerve and partly from the nuclei in
which this division ends—these fibers occupy the medial segment of the inferior peduncle and divide into ascending and
descending groups of fibers, the ascending fibers partly end in the roof nucleus of the opposite side of the cerebellum; (6)
cerebellobulbar fibers which come from the opposite roof nucleus and probably from the dentate nucleus, and are said to
end in the nucleus of Deiters and in the formatio reticularis of the medulla oblongata; (7) some fibers from the ventral
spinocerebellar fasciculus are said to join the dorsal spinocerebellar fasciculus.
The anterior medullary velum (velum medullare anterius; valve of Vieussens; superior medullary velum) is a thin,
transparent lamina of white substance, which stretches between the superior peduncle; on the dorsal surface of its lower
half the folia and lingula are prolonged. It forms, together with the superior peduncle, the roof of the upper part of the
fourth ventricle; it is narrow above, where it passes beneath the inferior colliculi, and broader below, where it is continuous
with the white substance of the superior vermis. A slightly elevated ridge, the fraenulum veli, descends upon its upper part
from between the inferior colliculi, and on either side of this the trochlear nerve emerges.
The posterior medullary velum (velum medullare posterius; inferior medullary velum) is a thin layer of white substance, prolonged from the white center of the cerebellum, above and on either side of the nodule; it forms a part of the roof
of the fourth ventricle. Somewhat semilunar in shape, its convex edge is continuous with the white substance of the cerebellum, while its thin concave margin is apparently free; in reality, however, it is continuous with the epithelium of the ventricle, which is prolonged downward from the posterior medullary velum to the ligulae.
The two medullary vela are in contact with each other along their line of emergence from the white substance of the
cerebellum; and this line of contact forms the summit of the roof of the fourth ventricle, which, in a vertical section through
the cavity, appears as a pointed angle.
The Fibrae Propriae of the cerebellum are of two kinds: (1) commissural fibers, which cross the middle line at the
anterior and posterior parts of the vermis and connect the opposite halves of the cerebellum; (2) arcuate or association
fibers, which connect adjacent laminae with each other.
Gray Substance.—The gray substance of the cerebellum is found in two situations: (1) on the surface, forming the
cortex; (2) as independent masses in the anterior.
(1) The gray substance of the cortex presents a characteristic foliated appearance, due to the series of laminae
which are given off from the central white substance; these in their turn give off secondary laminae, which are covered by
gray substance. Externally, the cortex is covered by pia mater; internally is the medullary center, consisting mainly of nerve
fibers.
Microscopic Appearance of the Cortex.—The cortex consists of two layers, viz., an external gray molecular layer,
and an internal rust-colored nuclear layer; between these is an incomplete stratum of cells which are characteristic of the
cerebellum, viz., the cells of Purkinje.
The external gray or molecular layer consists of fibers and cells. The nerve fibers are delicate fibrillae, and are derived from the following sources: (a) the dendrites and axon collaterals of Purkinje’s cells; (b) fibers from cells in the nuclear layer; (c) fibers from the central white substance of the cerebellum; (d) fibers derived from cells in the molecular layer
itself. In addition to these are other fibers, which have a vertical direction, and are the processes of large neuroglia cells,
situated in the nuclear layer. They pass outward to the periphery of the gray matter, where they expand into little conical
enlargements which form a sort of limiting membrane beneath the pia mater, analogous to the membrana limitans interna in
the retina, formed by the sustentacular fibers of Müller.
The cells of the molecular layer are small, and are arranged in two strata, an outer and an inner. They all possess
branched axons; those of the inner layer are termed basket cells; they run for some distance parallel with the surface of the
folium—giving off collaterals which pass in a vertical direction toward the bodies of Purkinje’s cells, around which they
become enlarged, and form basket-like net-works.
The cells of Purkinje form a single stratum of large, flask-shaped cells at the junction of the molecular and nuclear
layers, their bases resting against the latter; in fishes and reptiles they are arranged in several layers. The cells are flattened
in a direction transverse to the long axis of the folium, and thus appear broad in sections carried across the folium, and fusiform in sections parallel to the long axis of the folium. From the neck of the flask one or more dendrites arise and pass into
the molecular layer, where they subdivide and form an extremely rich arborescence, the various subdivisions of the dendrites being covered by lateral spinelike processes. This arborescence is not circular, but, like the cell, is flattened at right
angles to the long axis of the folium; in other words, it does not resemble a round bush, but has been aptly compared by
Obersteiner to the branches of a fruit tree trained against a trellis or a wall. Hence, in sections carried across the folium the
arborescence is broad and expanded; whereas in those which are parallel to the long axis of the folium, the arborescence,
like the cell itself, is seen in profile, and is limited to a narrow area.
From the bottom of the flask-shaped cell the axon arises; this passes through the nuclear layer, and, becoming medullated, is continued as a nerve fiber in the subjacent white substance. As this axon traverses the granular layer it gives off
fine collaterals, some of which run back into the molecular layer.
The internal rust-colored or nuclear layer is characterized by containing numerous small nerve cells of a reddishbrown color, together with many nerve fibrils. Most of the cells are nearly spherical and provided with short dendrites
which spread out in a spider-like manner in the nuclear layer. Their axons pass outward into the molecular layer, and, bifurcating at right angles, run for some distance parallel with the surface. In the outer part of the nuclear layer are some larger cells, of the type II of Golgi. Their axons undergo frequent division as soon as they leave the nerve cells, and pass into
the nuclear layer; while their dendrites ramify chiefly in the molecular layer.
Finally, in the gray substance of the cerebellar cortex there are fibers which come from the white center and penetrate the cortex. The cell-origin of these fibers is unknown, though it is believed that it is probably in the gray substance of
the medulla spinalis. Some of these fibers end in the nuclear layer by dividing into numerous branches, on which are to be
seen peculiar moss-like appendages; hence they have been termed by Ramón y Cajal the moss fibers; they form an arborescence around the cells of the nuclear layer and are said to come from fibers in the inferior peduncle. Other fibers, the
clinging or tendril fibers, derived from the medullary center can be traced into the molecular layer, where their branches
cling around the dendrites of Purkinje’s cells. They are said to come from fibers of the middle peduncle.
(2) The independent centers of gray substance in the cerebellum are four in number on either side: one is of large
size, and is known as the nucleus dentatus; the other three, much smaller, are situated near the middle of the cerebellum,
and are known as the nucleus emboliformis, nucleus globosus, and nucleus fastigii.
The nucleus dentatus is situated a little to the medial side of the center of the stem of the white substance of the
hemisphere. It consists of an irregularly folded lamina, of a grayish-yellow color, containing white fibers, and presenting on
its antero-medial aspect an opening, the hilus, from which most of the fibers of the superior peduncle emerge.
The nucleus emboliformis lies immediately to the medial side of the nucleus dentatus, and partly covering its hilus.
The nucleus globosus is an elongated mass, directed antero-posteriorly, and placed medial to preceding. The nucleus fastigii is somewhat larger than the other two, and is situated close to the middle line at the anterior end of the superior vermis,
and immediately over the roof of the fourth ventricle, from which it is separated by a thin layer of white substance.
The cerebellum is concerned with the coördination of movements necessary in equilibration, locomotion and prehension. In it terminate pathways conducting impulses of muscle sense, tendon sense, joint sense and equilibratory disturbances. With the exception of the ventral spinocerebellar fasciculus these impulses enter through the inferior peduncle. The
reflex arc is completed by fibers in the superior peduncle which pass to the red nucleus and the thalamus and thence by
additional neurons (rubrospinal tract) to the motor centers. The exact functions of its different parts are still quite uncertain,
owing to the contradictory nature of the evidence furnished by (1) ablation experiments upon animals, and (2) clinical observations in man of the effects produced by abscesses or tumors affecting different portions of the organ.
Practice skills
Students are supposed to identify the following structures on the samples:
- brainstem
- posterior median fissure
- medulla oblongata
- inferior cerebellar peduncle
- pons
- pons
- mid-brain
- basilar sulcus
- medulla oblongata
- middle cerebellar peduncle
- anterior median fissure
- superior cerebellar peduncle
- pyramid
- superior medullary velum
- decussation of pyramids
- tegmentum of pons (on a transverse
- anterolateral sulcus
section)
- inferior olive
- basilar part of pons
- posterolateral sulcus
- cerebellum
- cuneate fasciculus
- hemisphere of cerebellum
- cuneate tubercle
- vermis of cerebellum
- gracile fasciculus
- cerebellar fissures
- gracile tubercle
- folia of cerebellum
-
flocculus
arbor vitae
-
cerebellar cortex
dentate nucleus
Practice class 2. The rhomboid fossa. ІV ventricle. The topography of the cranial nerves
nuclei.
The aim: to learn the structure and topography of the rhomboid fossa and the IV ventricle; to find out the
topography of cranial nerves’ nuclei.
Professional orientation: the knowledge of this topic is necessary for doctors of all specialities; it represents special interest for therapists.
The plan of the practice class:
A. Checking of the home assignment: oral quiz or written test control – 30 minutes.
B. Summary lecture on the topic by teacher – 30 minutes.
a) The rhomboid fossa.
b) The IV ventricle.
c) The choroid plexus.
C. Students’ self-taught time – 55 minutes
D. Home-task – 5 minutes
Rhomboid Fossa (fossa rhomboidea; “floor” of the fourth ventricle).—The anterior part of the fourth ventricle is
named, from its shape, the rhomboid fossa, and its anterior wall, formed by the back of the pons and medulla oblongata,
constitutes the floor of the fourth ventricle. It is covered by a thin layer of gray substance continuous with that of the medulla spinalis; superficial to this is a thin lamina of neuroglia which constitutes the ependyma of the ventricle and supports
a layer of ciliated epithelium. The fossa consists of three parts, superior, intermediate, and inferior. The superior part is
triangular in shape and limited laterally by the superior cerebellar peduncle; its apex, directed upward, is continuous with
the cerebral aqueduct; its base it represented by an imaginary line at the level of the upper ends of the superior foveae. The
intermediate part extends from this level to that of the horizontal portions of the taeniae of the ventricle; it is narrow above
where it is limited laterally by the middle peduncle, but widens below and is prolonged into the lateral recesses of the ventricle. The inferior part is triangular, and its downwardly directed apex, named the calamus scriptorius, is continuous with
the central canal of the closed part of the medulla oblongata.
The rhomboid fossa is divided into symmetrical halves by a median sulcus which reaches from the upper to the
lower angles of the fossa and is deeper below than above. On either side of this sulcus is an elevation, the medial eminence, bounded laterally by a sulcus, the sulcus limitans. In the superior part of the fossa the medial eminence has a width
equal to that of the corresponding half of the fossa, but opposite the superior fovea it forms an elongated swelling, the colliculus facialis, which overlies the nucleus of the abducent nerve, and is, in part at least, produced by the ascending portion
of the root of the facial nerve. In the inferior part of the fossa the medial eminence assumes the form of a triangular area,
the trigonum hypoglossi. When examined under water with a lens this trigone is seen to consist of a medial and a lateral
area separated by a series of oblique furrows; the medial area corresponds with the upper part of the nucleus of the hypoglossal nerve, the lateral with a small nucleus, the nucleus intercalatus.
The sulcus limitans forms the lateral boundary of the medial eminence. In the superior part of the rhomboid fossa it
corresponds with the lateral limit of the fossa and presents a bluish-gray area, the locus caeruleus, which owes its color to
an underlying patch of deeply pigmented nerve cells, termed the substantia ferruginea. At the level of the colliculus facialis the sulcus limitans widens into a flattened depression, the superior fovea, and in the inferior part of the fossa appears
as a distinct dimple, the inferior fovea. Lateral to the foveae is a rounded elevation named the area acustica, which extends into the lateral recess and there forms a feebly marked swelling, the tuberculum acusticum. Winding around the
inferior peduncle and crossing the area acustica and the medial eminence are a number of white strands, the striae medullares, which form a portion of the cochlear division of the acoustic nerve and disappear into the median sulcus. Below the
inferior fovea, and between the trigonum hypoglossi and the lower part of the area acustica is a triangular dark field, the ala
cinerea, which corresponds to the sensory nucleus of the vagus and glossopharyngeal nerves. The lower end of the ala cinerea is crossed by a narrow translucent ridge, the funiculus separans, and between this funiculus and the clava, is a small
tongue-shaped area, the area postrema. On section it is seen that the funiculus separans is formed by a strip of thickened
ependyma, and the area postrema by loose, highly vascular, neuroglial tissue containing nerve cells of moderate size.
The Fourth Ventricle (ventriculus quartus).—The fourth ventricle, or cavity of the hind-brain, is situated in front
of the cerebellum and behind the pons and upper half of the medulla oblongata. Developmentally considered, the fourth
ventricle consists of three parts: a superior belonging to the isthmus rhombencephali, an intermediate, to the metencephalon, and an inferior, to the myelencephalon. It is lined by ciliated epithelium, and is continuous below with the central canal of the medulla oblongata; above, it communicates, by means of a passage termed the cerebral aqueduct, with the cavity
of the third ventricle. It presents four angles, and possesses a roof or dorsal wall, a floor or ventral wall, and lateral
boundaries.
Angles.—The superior angle is on a level with the upper border of the pons, and is continuous with the lower end
of the cerebral aqueduct. The inferior angle is on a level with the lower end of the olive, and opens into the central canal of
the medulla oblongata. Each lateral angle corresponds with the point of meeting of the brachia and inferior peduncle. A
little below the lateral angles, on a level with the striae medullares, the ventricular cavity is prolonged outward in the form
of two narrow lateral recesses, one on either side; these are situated between the inferior peduncles and the flocculi, and
reach as far as the attachments of the glossopharyngeal and vagus nerves.
Lateral Boundaries.—The lower part of each lateral boundary is constituted by the clava, the fasciculus cuneatus,
and the inferior peduncle; the upper part by the middle and the superior peduncle.
Roof or Dorsal Wall.—The upper portion of the roof is formed by the superior peduncle and the anterior medullary
velum; the lower portion, by the posterior medullary velum, the epithelial lining of the ventricle covered by the tela chorioidea inferior, the taeniae of the fourth ventricle, and the obex.
The superior peduncle, on emerging from the central white substance of the cerebellum, pass upward and forward,
forming at first the lateral boundaries of the upper part of the cavity; on approaching the inferior colliculi, they converge,
and their medial portions overlap the cavity and form part of its roof.
The anterior medullary velum fills in the angular interval between the superior peduncle, and is continuous behind
with the central white substance of the cerebellum; it is covered on its dorsal surface by the lingula of the superior vermis.
The posterior medullary velum is continued downward and forward from the central white substance of the cerebellum in front of the nodule and tonsils, and ends inferiorly in a thin, concave, somewhat ragged margin. Below this margin the roof is devoid of nervous matter except in the immediate vicinity of the lower lateral boundaries of the ventricle,
where two narrow white bands, the taeniae of the fourth ventricle (ligulae), appear; these bands meet over the inferior
angle of the ventricle in a thin triangular lamina, the obex. The non-nervous part of the roof is formed by the epithelial
lining of the ventricle, which is prolonged downward as a thin membrane, from the deep surface of the posterior medullary velum to the corresponding surface of the obex and taeniae, and thence on to the floor of the ventricular cavity; it is
covered and strengthened by a portion of the pia mater, which is named the tela chorioidea of the fourth ventricle.
The taeniae of the fourth ventricle (taenia ventriculi quarti; ligula) are two narrow bands of white matter, one on
either side, which complete the lower part of the roof of the cavity. Each consists of a vertical and a horizontal part. The
vertical part is continuous below the obex with the clava, to which it is adherent by its lateral border. The horizontal portion
extends transversely across the inferior peduncle, below the striae medullares, and roofs in the lower and posterior part of
the lateral recess; it is attached by its lower margin to the inferior peduncle, and partly encloses the choroid plexus, which,
however, projects beyond it like a cluster of grapes; and hence this part of the taenia has been termed the cornucopia
(Bochdalek). The obex is a thin, triangular, gray lamina, which roofs in the lower angle of the ventricle and is attached by
its lateral margins to the clavae. The tela chorioidea of the fourth ventricle is the name applied to the triangular fold of
pia mater which is carried upward between the cerebellum and the medulla oblongata. It consists of two layers, which are
continuous with each other in front, and are more or less adherent throughout. The posterior layer covers the antero-inferior
surface of the cerebellum, while the anterior is applied to the structures which form the lower part of the roof of the ventricle, and is continuous inferiorly with the pia mater on the inferior peduncles and closed part of the medulla.
Choroid Plexuses.—These consist of two highly vascular inflexions of the tela chorioidea, which invaginate the
lower part of the roof of the ventricle and are everywhere covered by the epithelial lining of the cavity. Each consists of a
vertical and a horizontal portion: the former lies close to the middle line, and the latter passes into the lateral recess and
projects beyond its apex. The vertical parts of the plexuses are distinct from each other, but the horizontal portions are
joined in the middle line; and hence the entire structure presents the form of the letter T, the vertical limb of which, however, is double.
Openings in the Roof.—In the roof of the fourth ventricle there are three openings, a medial and two lateral: the
medial aperture (foramen Majendii), is situated immediately above the inferior angle of the ventricle; the lateral apertures, (foramina of Luschka are found at the extremities of the lateral recesses. By means of these three openings the ventricle communicates with the subarachnoid cavity, and the cerebrospinal fluid can circulate from the one to the other.
Practice skills
Students are supposed to identify the following structures on the samples and schemas:
- IV ventricle
- vagal trigone
- rhomboid fossa
- lateral recess
- median sulcus
- facial colliculus
- medial eminence of the rhomboid
- vestibular area
fossa
- roof of the IV ventricle
- medullar stria of the IV ventricle
- superior medullary velum
- hypoglossal trigone
- inferior medullary velum
Practice class 3. The diencephalon. ІІІ ventricle.
The aim: to learn the structure and topography of the diencephalon and the III ventricle.
Professional orientation: the knowledge of this topic is necessary for doctors of all specialities; it represents special interest for therapists.
The plan of the practice class:
A. Checking of the home assignment: oral quiz or written test control – 30 minutes.
B. Summary lecture on the topic by teacher – 30 minutes.
a) The diencephalon.
b) The thalamencephalon.
c) The third ventricle.
C. Students’ self-taught time – 55 minutes
D. Home-task – 5 minutes
The Diencephalon.—The diencephalon is connected above and in front with the cerebral hemispheres; behind with
the mid-brain. Its upper surface is concealed by the corpus callosum, and is covered by a fold of pia mater, named the tela
chorioidea of the third ventricle; inferiorly it reaches to the base of the brain.
The diencephalon comprises: (1) the thalamencephalon; (2) the pars mamillaris hypothalami; and (3) the posterior part of the third ventricle. For descriptive purposes, however, it is more convenient to consider the whole of the third
ventricle and its boundaries together; this necessitates the inclusion, under this heading, of the pars optica hypothalami and
the corresponding part of the third ventricle—structures which properly belong to the telencephalon.
The Thalamencephalon.—The thalamencephalon comprises: (1) the thalamus; (2) the metathalamus or corpora
geniculata; and (3) the epithalamus, consisting of the trigonum habenulae, the pineal body, and the posterior commissure.
The Thalami (optic thalamus) are two large ovoid masses, situated one on either side of the third ventricle and
reaching for some distance behind that cavity. Each measures about 4 cm. in length, and presents two extremities, an anterior and a posterior, and four surfaces, superior, inferior, medial, and lateral.
The anterior extremity is narrow; it lies close to the middle line and forms the posterior boundary of the interventricular foramen.
The posterior extremity is expanded, directed backward and lateralward, and overlaps the superior colliculus. Medially it presents an angular prominence, the pulvinar, which is continued laterally into an oval swelling, the lateral geniculate body, while beneath the pulvinar, but separated from it by the superior brachium, is a second oval swelling, the
medial geniculate body.
The superior surface is free, slightly convex, and covered by a layer of white substance, termed the stratum zonale. It is separated laterally from the caudate nucleus by a white band, the stria terminalis, and by the terminal vein. It is
divided into a medial and a lateral portion by an oblique shallow furrow which runs from behind forward and medialward
and corresponds with the lateral margin of the fornix; the lateral part forms a portion of the floor of the lateral ventricle, and
is covered by the epithelial lining of this cavity; the medial part is covered by the tela chorioidea of the third ventricle, and
is destitute of an epithelial covering. In front, the superior is separated from the medial surface by a salient margin, the taenia thalami, along which the epithelial lining of the third ventricle is reflected on to the under surface of the tela chorioidea. Behind, it is limited medially by a groove, the sulcus habenulae, which intervenes between it and a small triangular
area, termed the trigonum habenulae.
The inferior surface rests upon and is continuous with the upward prolongation of the tegmentum (subthalamic
tegmental region), in front of which it is related to the substantia innominata of Meynert.
The medial surface constitutes the upper part of the lateral wall of the third ventricle, and is connected to the corresponding surface of the opposite thalamus by a flattened gray band, the massa intermedia (middle or gray commissure).
This mass averages about 1 cm. in its antero-posterior diameter: it sometimes consists of two parts and occasionally is absent. It contains nerve cells and nerve fibers; a few of the latter may cross the middle line, but most of them pass toward the
middle line and then curve lateralward on the same side.
The lateral surface is in contact with a thick band of white substance which forms the occipital part of the internal
capsule and separates the thalamus from the lentiform nucleus of the corpus striatum.
Structure.—The thalamus consists chiefly of gray substance, but its upper surface is covered by a layer of white
substance, named the stratum zonale, and its lateral surface by a similar layer termed the lateral medullary lamina. Its
gray substance is incompletely subdivided into three parts—anterior, medial, and lateral—by a white layer, the medial medullary lamina. The anterior part comprises the anterior tubercle, the medial part lies next the lateral wall of the third ventricle while the lateral and largest part is interposed between the medullary laminae and includes the pulvinar. The lateral
part is traversed by numerous fibers which radiate from the thalamus into the internal capsule, and pass through the latter to
the cerebral cortex. These three parts are built up of numerous nuclei, the connections of many of which are imperfectly
known.
Connections.—The thalamus may be regarded as a large ganglionic mass in which the ascending tracts of the tegmentum and a considerable proportion of the fibers of the optic tract end, and from the cells of which numerous fibers
(thalamocortical) take origin, and radiate to almost every part of the cerebral cortex. The lemniscus, together with the other
longitudinal strands of the tegmentum, enters its ventral part: the thalamomammillary fasciculus (bundle of Vicq d’Azyr),
from the corpus mammillare, enters in its anterior tubercle, while many of the fibers of the optic tract terminate in its posterior end. The thalamus also receives numerous fibers (corticothalamic) from the cells of the cerebral cortex. The fibers that
arise from the cells of the thalamus form four principal groups or stalks: (a) those of the anterior stalk pass through the
frontal part of the internal capsule to the frontal lobe; (b) the fibers of the posterior stalk (optic radiations) arise in the pulvinar and are conveyed through the occipital part of the internal capsule to the occipital lobe; (c) the fibers of the inferior
stalk leave the under and medial surfaces of the thalamus, and pass beneath the lentiform nucleus to the temporal lobe and
insula; (d) those of the parietal stalk pass from the lateral nucleus of the thalamus to the parietal lobe. Fibers also extend
from the thalamus into the corpus striatum—those destined for the caudate nucleus leave the lateral surface, and those for
the lentiform nucleus, the inferior surface of the thalamus.
The Metathalamus comprises the geniculate bodies, which are two in number—a medial and a lateral—on each
side.
The medial geniculate body (corpus geniculatum mediale; internal geniculate body; postgeniculatum) lies under
cover of the pulvinar of the thalamus and on the lateral aspect of the corpora quadrigemina. Oval in shape, with its long
axis directed forward and lateralward, it is lighter in color and smaller in size than the lateral. The inferior brachium from
the inferior colliculus disappears under cover of it while from its lateral extremity a strand of fibers passes to join the optic
tract. Entering it are many acoustic fibers from the lateral lemniscus. The medial geniculate bodies are connected with one
another by the commissure of Gudden, which passes through the posterior part of the optic chiasma.
The lateral geniculate body (corpus geniculatum laterale; external geniculate body; pregeniculatum) is an oval elevation on the lateral part of the posterior end of the thalamus, and is connected with the superior colliculus by the superior
brachium. It is of a dark color, and presents a laminated arrangement consisting of alternate layers of gray and white substance. It receives numerous fibers from the optic tract, while other fibers of this tract pass over or through it into the pulvinar. Its cells are large and pigmented; their axons pass to the visual area in the occipital part of the cerebral cortex.
The superior colliculus, the pulvinar, and the lateral geniculate body receive many fibers from the optic tracts, and
are therefore intimately connected with sight, constituting what are termed the lower visual centers. Extirpation of the eyes
in a newly born animal entails an arrest of the development of these centers, but has no effect on the medial geniculate bodies or on the inferior colliculi. Moreover, the latter are well-developed in the mole, an animal in which the superior colliculi
are rudimentary.
The Epithalamus comprises the trigonum habenulae, the pineal body, and the posterior commissure.
The trigonum habenulae is a small depressed triangular area situated in front of the superior colliculus and on the
lateral aspect of the posterior part of the taenia thalami. It contains a group of nerve cells termed the ganglion habenulae.
Fibers enter it from the stalk of the pineal body, and others, forming what is termed the habenular commissure, pass
across the middle line to the corresponding ganglion of the opposite side. Most of its fibers are, however, directed downward and form a bundle, the fasciculus retroflexus of Meynert, which passes medial to the red nucleus, and, after decussating with the corresponding fasciculus of the opposite side, ends in the interpeduncular ganglion.
The pineal body (corpus pineale; epiphysis) is a small, conical, reddish-gray body which lies in the depression between the superior colliculi. It is placed beneath the splenium of the corpus callosum, but is separated from this by the tela
chorioidea of the third ventricle, the lower layer of which envelops it. It measures about 8 mm. in length, and its base, directed forward, is attached by a stalk or peduncle of white substance. The stalk of the pineal body divides anteriorly into
two laminae, a dorsal and a ventral, separated from one another by the pineal recess of the third ventricle. The ventral lamina is continuous with the posterior commissure; the dorsal lamina is continuous with the habenular commissure and divides
into two strands the medullary striae, which run forward, one on either side, along the junction of the medial and upper
surfaces of the thalamus to blend in front with the columns of the fornix.
The posterior commissure is a rounded band of white fibers crossing the middle line on the dorsal aspect of the upper end of the cerebral aqueduct. Its fibers acquire their medullary sheaths early, but their connections have not been definitely determined. Most of them have their origin in a nucleus, the nucleus of the posterior commissure (nucleus of
Darkschewitsch), which lies in the central gray substance of the upper end of the cerebral aqueduct, in front of the nucleus
of the oculomotor nerve. Some are probably derived from the posterior part of the thalamus and from the superior colliculus, while others are believed to be continued downward into the medial longitudinal fasciculus.
The Hypothalamus includes the subthalamic tegmental region and the structures forming the greater part of the
floor of the third ventricle, viz., the corpora mammillaria, tuber cinereum, infundibulum, hypophysis, and optic chiasma.
The subthalamic tegmental region consists of the upward continuation of the tegmentum; it lies on the ventrolateral aspect of the thalamus and separates it from the fibers of the internal capsule. The red nucleus and the substantia
nigra are prolonged into its lower part; in front it is continuous with the substantia innominata of Meynert, medially with
the gray substance of the floor of the third ventricle.
It consists from above downward of three strata: (1) stratum dorsale, directly applied to the under surface of the
thalamus and consisting of fine longitudinal fibers; (2) zona incerta, a continuation forward of the formatio reticularis of
the tegmentum; and (3) the corpus subthalamicum (nucleus of Luys), a brownish mass presenting a lenticular shape on
transverse section, and situated on the dorsal aspect of the fibers of the base of the cerebral peduncle; it is encapsuled by a
lamina of nerve fibers and contains numerous medium-sized nerve cells, the connections of which are as yet not fully determined.
The corpora mammillaria (corpus albicantia) are two round white masses, each about the size of a small pea,
placed side by side below the gray substance of the floor of the third ventricle in front of the posterior perforated substance.
They consist of white substance externally and of gray substance internally, the cells of the latter forming two nuclei, a
medial of smaller and a lateral of larger cells. The white substance is mainly formed by the fibers of the columns of the
fornix, which descend to the base of the brain and end partly in the corpora mammillaria. From the cells of the gray substance of each mammillary body two fasciculi arise: one, the thalamomammillary fasciculus (bundle of Vicq d’Azyr),
passes upward into the anterior nucleus of the thalamus; the other is directed downward into the tegmentum. Afferent fibers
are believed to reach the corpus mammillare from the medial lemniscus and from the tegmentum.
The tuber cinereum is a hollow eminence of gray substance situated between the corpora mammillaria behind, and
the optic chiasma in front. Laterally it is continuous with the anterior perforated substances and anteriorly with a thin lamina, the lamina terminalis. From the under surface of the tuber cinereum a hollow conical process, the infundibulum, projects downward and forward and is attached to the posterior lobe of the hypophysis.
In the lateral part of the tuber cinereum is a nucleus of nerve cells, the basal optic nucleus of Meynert, while close
to the cavity of the third ventricle are three additional nuclei. Between the tuber cinereum and the corpora mammillaria a
small elevation, with a corresponding depression in the third ventricle, is sometimes seen. Retzius has named it the eminentia saccularis, and regards it as a representative of the saccus vasculosus found in this situation in some of the lower
vertebrates.
The hypophysis (pituitary body) is a reddish-gray, somewhat oval mass, measuring about 12.5 mm. in its transverse, and about 8 mm. in its antero-posterior diameter. It is attached to the end of the infundibulum, and is situated in the
fossa hypophyseos of the sphenoidal bone, where it is retained by a circular fold of dura mater, the diaphragma sella; this
fold almost completely roofs in the fossa, leaving only a small central aperture through which the infundibulum passes.
Optic Chiasma (chiasma opticum; optic commissure).—The optic chiasma is a flattened, somewhat quadrilateral
band of fibers, situated at the junction of the floor and anterior wall of the third ventricle. Most of its fibers have their origins in the retina, and reach the chiasma through the optic nerves, which are continuous with its antero-lateral angles. In the
chiasma, they undergo a partial decussation, the fibers from the nasal half of the retina decussate and enter the optic tract of
the opposite side, while the fibers from the temporal half of the retina do not undergo decussation, but pass back into the
optic tract of the same side. Occupying the posterior part of the commissure, however, is a strand of fibers, the commissure
of Gudden, which is not derived from the optic nerves; it forms a connecting link between the medial geniculate bodies.
Optic Tracts.—The optic tracts are continued backward and lateralward from the postero-lateral angles of the optic
chiasma. Each passes between the anterior perforated substance and the tuber cinereum, and, winding around the ventrolateral aspect of the cerebral peduncle, divides into a medial and a lateral root. The former comprises the fibers of Gudden’s commissure. The lateral root consists mainly of afferent fibers which arise in the retina and undergo partial decussation in the optic chiasma, as described; but it also contains a few fine efferent fibers which have their origins in the brain
and their terminations in the retina. When traced backward, the afferent fibers of the lateral root are found to end in the lateral geniculate body and pulvinar of the thalamus, and in the superior colliculus; and these three structures constitute the
lower visual centers. Fibers arise from the nerve cells in these centers and pass through the occipital part of the internal
capsule, under the name of the optic radiations, to the cortex of the occipital lobe of the cerebrum, where the higher or
cortical visual center is situated. Some of the fibers of the optic radiations take an opposite course, arising from the cells
of the occipital cortex and passing to the lower visual centers. Some fibers are detached from the optic tract, and pass
through the cerebral peduncle to the nucleus of the oculomotor nerve. These may be regarded as the afferent branches for
the Sphincter pupillae and Ciliaris muscles. Other fibers have been described as reaching the cerebellum through the superior peduncle; while others, again, are lost in the pons.
The Third Ventricle (ventriculus tertius).—The third ventricle is a median cleft between the two thalami. Behind,
it communicates with the fourth ventricle through the cerebral aqueduct, and in front with the lateral ventricles through the
interventricular foramen. Somewhat triangular in shape, with the apex directed backward, it has a roof, a floor, an anterior
and a posterior boundary and a pair of lateral walls.
The roof is formed by a layer of epithelium, which stretches between the upper edges of the lateral walls of the cavity and is continuous with the epithelial lining of the ventricle. It is covered by and adherent to a fold of pia mater, named
the tela chorioidea of the third ventricle, from the under surface of which a pair of vascular fringed processes, the choroid
plexuses of the third ventricle, project downward, one on either side of the middle line, and invaginate the epithelial roof
into the ventricular cavity.
The floor slopes downward and forward and is formed mainly by the structures which constitute the hypothalamus:
from before backward these are: the optic chiasma, the tuber cinereum and infundibulum, and the corpora mammillaria.
Behind the last, the floor is formed by the interpeduncular fossa and the tegmenta of the cerebral peduncles. The ventricle is
prolonged downward as a funnel-shaped recess, the recessus infundibuli, into the infundibulum, and to the apex of the
latter the hypophysis is attached.
The anterior boundary is constituted below by the lamina terminalis, a thin layer of gray substance stretching
from the upper surface of the optic chiasma to the rostrum of the corpus callosum; above by the columns of the fornix and
the anterior commissure. At the junction of the floor and anterior wall, immediately above the optic chiasma, the ventricle
presents a small angular recess or diverticulum, the optic recess. Between the columns of the fornix, and above the anterior
commissure, is a second recess termed the vulva. At the junction of the roof and anterior wall of the ventricle, and situated
between the thalami behind and the columns of the fornix in front, is the interventricular foramen (foramen of Monro)
through which the third communicates with the lateral ventricles.
The posterior boundary is constituted by the pineal body, the posterior commissure and the cerebral aqueduct. A
small recess, the recessus pinealis, projects into the stalk of the pineal body, while in front of and above the pineal body is
a second recess, the recessus suprapinealis, consisting of a diverticulum of the epithelium which forms the ventricular
roof.
Each lateral wall consists of an upper portion formed by the medial surface of the anterior two-thirds of the thalamus, and a lower consisting of an upward continuation of the gray substance of the ventricular floor. These two parts correspond to the alar and basal laminae respectively of the lateral wall of the fore-brain vesicle and are separated from each
other by a furrow, the sulcus of Monro, which extends from the interventricular foramen to the cerebral aqueduct. The
lateral wall is limited above by the taenia thalami. The columns of the fornix curve downward in front of the interventricular foramen, and then run in the lateral walls of the ventricle, where, at first, they form distinct prominences, but subsequently are lost to sight. The lateral walls are joined to each other across the cavity of the ventricle by a band of gray matter, the massa intermedia.
Interpeduncular Fossa.—This is a somewhat lozenge-shaped area of the base of the brain, limited in front by the optic
chiasma, behind by the antero-superior surface of the pons, antero-laterally by the converging optic tracts, and posterolaterally by the diverging cerebral peduncles. The structures contained in it have already been described; from behind forward, they are the posterior perforated substance, corpora mamillaria, tuber cinereum, infundibulum, and hypophysis.
Practice skills
Students are supposed to identify the following structures on the samples and schemas:
the diencephalon
- medial geniculate body
- thalamus
- hypothalamus
- anterior thalamic tubercle
- optic chiasm
- pulvinar
- optic tract
- stria medullaris of thalamus
- tuber cinereum
- epithalamus
- infundibulum
- habenula
- mamillary body
- habenular trigone
the third venticle
- pineal gland
- the walls of the third ventricle
- metathalamus
- interventricular foramen
- lateral geniculate body
- foramen of the cerebral aqueduct
Practice class 4. The anatomy of forebrain: the grooves and gyri. The basal ganglions and
white matter of the forebrain. The lateral ventricles.
The aim: to learn the structure and topography of the forebrain, the basal ganglions, the white matter of
the forebrain and the lateral ventricles; to learn the grooves and gyri of cerebral hemispheres and find out the
dynamic localization of functions in the cerebral cortex.
Professional orientation: the knowledge of this topic is necessary for doctors of all specialities; it represents special interest for therapists.
The plan of the practice class:
A. Checking of the home assignment: oral quiz or written test control – 30 minutes.
B. Summary lecture on the topic by teacher – 30 minutes.
a) The telencephalon.
b) The cerebral hemispheres
c) The basal ganglions and the white matter of the telencephalon.
d) The lateral ventricles
C. Students’ self-taught time – 55 minutes
D. Home-task – 5 minutes
The fore-brain or prosencephalon consists of: (1) the diencephalon, corresponding in a large measure to the third
ventricle and the structures which bound it; and (2) the telencephalon, comprising the largest part of the brain, viz., the
cerebral hemispheres; these hemispheres are intimately connected with each other across the middle line, and each contains
a large cavity, named the lateral ventricle. The lateral ventricles communicate through the interventricular foramen with the
third ventricle, but are separated from each other by a medial septum, the septum pellucidum; this contains a slit-like cavity, which does not communicate with the ventricles.
The Telencephalon.—The telencephalon includes: (1) the cerebral hemispheres with their cavities, the lateral
ventricles; and (2) the pars optica hypothalami and the anterior portion of the third ventricle (already described under the
diencephalon). As previously stated, each cerebral hemisphere may be divided into three fundamental parts, viz., the rhinencephalon, the corpus striatum, and the neopallium. The rhinencephalon, associated with the sense of smell, is the oldest
part of the telencephalon, and forms almost the whole of the hemisphere in some of the lower animals, e. g., fishes, amphibians, and reptiles. In man it is rudimentary, whereas the neopallium undergoes great development and forms the chief
part of the hemisphere.
The Cerebral Hemispheres.—The cerebral hemispheres constitute the largest part of the brain, and, when viewed
together from above, assume the form of an ovoid mass broader behind than in front, the greatest transverse diameter corresponding with a line connecting the two parietal eminences. The hemispheres are separated medially by a deep cleft, named
the longitudinal cerebral fissure, and each possesses a central cavity, the lateral ventricle.
The Longitudinal Cerebral Fissure (fissura cerebri longitudinalis; great longitudinal fissure) contains a sickleshaped process of dura mater, the falx cerebri. It front and behind, the fissure extends from the upper to the under surfaces
of the hemispheres and completely separates them, but its middle portion separates them for only about one-half of their
vertical extent; for at this part they are connected across the middle line by a great central white commissure, the corpus
callosum.
In a median sagittal section the cut corpus callosum presents the appearance of a broad, arched band. Its thick posterior end, termed the splenium, overlaps the mid-brain, but is separated from it by the tela chorioidea of the third ventricle
and the pineal body. Its anterior curved end, termed the genu, gradually tapers into a thinner portion, the rostrum, which is
continued downward and backward in front of the anterior commissure to join the lamina terminalis. Arching backward
from immediately behind the anterior commissure to the under surface of the splenium is a second white band named the
fornix: between this and the corpus callosum are the laminae and cavity of the septum pellucidum.
Surfaces of the Cerebral Hemispheres.—Each hemisphere presents three surfaces: lateral, medial, and inferior.
The lateral surface is convex in adaptation to the concavity of the corresponding half of the vault of the cranium.
The medial surface is flat and vertical, and is separated from that of the opposite hemisphere by the great longitudinal fissure and the falx cerebri. The inferior surface is of an irregular form, and may be divided into three areas: anterior, middle,
and posterior. The anterior area, formed by the orbital surface of the frontal lobe, is concave, and rests on the roof of the
orbit and nose; the middle area is convex, and consists of the under surface of the temporal lobe: it is adapted to the corresponding half of the middle cranial fossa. The posterior area is concave, directed medialward as well as downward, and is
named the tentorial surface, since it rests upon the tentorium cerebelli, which intervenes between it and the upper surface
of the cerebellum.
These three surfaces are separated from each other by the following borders: (a) supero-medial, between the lateral and medial surfaces; (b) infero-lateral, between the lateral and inferior surfaces; the anterior part of this border separating the lateral from the orbital surface, is known as the superciliary border; (c) medial occipital, separating the medial
and tentorial surfaces; and (d) medial orbital, separating the orbital from the medial surface. The anterior end of the hemisphere is named the frontal pole; the posterior, the occipital pole; and the anterior end of the temporal lobe, the temporal
pole. About 5 cm. in front of the occipital pole on the infero-lateral border is an indentation or notch, named the preoccipital notch.
The surfaces of the hemispheres are moulded into a number of irregular eminences, named gyri or convolutions,
and separated by furrows termed fissures and sulci. The furrows are of two kinds, complete and incomplete. The former
appear early in fetal life, are few in number, and are produced by infoldings of the entire thickness of the brain wall, and
give rise to corresponding elevations in the interior of the ventricle. They comprise the hippocampal fissure, and parts of
the calcarine and collateral fissures. The incomplete furrows are very numerous, and only indent the subjacent white substance, without producing any corresponding elevations in the ventricular cavity.
The gyri and their intervening fissures and the sulci are fairly constant in their arrangement; at the same time they
vary within certain limits, not only in different individuals, but on the two hemispheres of the same brain. The convoluted
condition of the surface permits of a great increase of the gray matter without the sacrifice of much additional space. The
number and extent of the gyri, as well as the depth of the intervening furrows, appear to bear a direct relation to the intellectual powers of the individual.
Certain of the fissures and sulci are utilized for the purpose of dividing the hemisphere into lobes, and are therefore
termed interlobular; included under this category are the lateral cerebral, parietoöccipital, calcarine, and collateral fissures,
the central and cingulate sulci, and the sulcus circularis.
The Lateral Cerebral Fissure (fissura cerebri lateralis [Sylvii]; fissure of Sylvius) is a well-marked cleft on the inferior and lateral surfaces of the hemisphere, and consists of a short stem which divides into three rami. The stem is situated on the base of the brain, and commences in a depression at the lateral angle of the anterior perforated substance. From
this point it extends between the anterior part of the temporal lobe and the orbital surface of the frontal lobe, and reaches
the lateral surface of the hemisphere. Here it divides into three rami: an anterior horizontal, an anterior ascending, and a
posterior. The anterior horizontal ramus passes foward for about 2.5 cm. into the inferior frontal gyrus, while the anterior ascending ramus extends upward into the same convolution for about an equal distance. The posterior ramus is the
longest; it runs backward and slightly upward for about 7 cm., and ends by an upward inflexion in the parietal lobe.
The Central Sulcus (sulcus centralis [Rolandi]; fissure of Rolando; central fissure) is situated about the middle of
the lateral surface of the hemisphere, and begins in or near the longitudinal cerebral fissure, a little behind its mid-point. It
runs sinuously downward and forward, and ends a little above the posterior ramus of the lateral fissure, and about 2.5 cm.
behind the anterior ascending ramus of the same fissure. It described two chief curves: a superior genu with its concavity
directed forward, and an inferior genu with its concavity directed backward. The central sulcus forms an angle opening
forward of about 70° with the median plane.
The Parietoöccipital Fissure (fissura parietoöccipitalis).—Only a small part of this fissure is seen on the lateral
surface of the hemisphere, its chief part being on the medial surface.
The lateral part of the parietoöccipital fissure is situated about 5 cm. in front of the occipital pole of the hemisphere, and measures about 1.25 cm. in length.
The medial part of the parietoöccipital fissure runs downward and forward as a deep cleft on the medial surface of
the hemisphere, and joins the calcarine fissure below and behind the posterior end of the corpus callosum. In most cases it
contains a submerged gyrus.
The Calcarine Fissure (fissura calcarina) is on the medial surface of the hemisphere. It begins near the occipital
pole in two converging rami, and runs forward to a point a little below the splenium of the corpus callosum, where it is
joined at an acute angle by the medial part of the parietoöccipital fissure. The anterior part of this fissure gives rise to the
prominence of the calcar avis in the posterior cornu of the lateral ventricle.
The Cingulate Sulcus (sulcus cinguli; callosomarginal fissure) is on the medial surface of the hemisphere; it begins
below the anterior end of the corpus callosum and runs upward and forward nearly parallel to the rostrum of this body and,
curving in front of the genu, is continued backward above the corpus callosum, and finally ascends to the supero-medial
border of the hemisphere a short distance behind the upper end of the central sulcus. It separates the superior frontal from
the cingulate gyrus.
The Collateral Fissure (fissura collateralis) is on the tentorial surface of the hemisphere and extends from near the
occipital pole to within a short distance of the temporal pole. Behind, it lies below and lateral to the calcarine fissure, from
which it is separated by the lingual gyrus; in front, it is situated between the hippocampal gyrus and the anterior part of the
fusiform gyrus.
The Sulcus Circularis (circuminsular fissure) is on the lower and lateral surfaces of the hemisphere: it surrounds
the insula and separates it from the frontal, parietal, and temporal lobes.
Lobes of the Hemispheres.—By means of these fissures and sulci, assisted by certain arbitrary lines, each hemisphere is divided into the following lobes: the frontal, the parietal, the temporal, the occipital, the limbic, and the insula.
Frontal Lobe (lobus frontalis).—On the lateral surface of the hemisphere this lobe extends from the frontal pole to
the central sulcus, the latter separating it from the parietal lobe. Below, it is limited by the posterior ramus of the lateral
fissure, which intervenes between it and the central lobe. On the medial surface, it is separated from the cingulate gyrus by
the cingulate sulcus; and on the inferior surface, it is bounded behind by the stem of the lateral fissure.
The lateral surface of the frontal lobe is tranversed by three sulci which divide it into four gyri: the sulci are named
the precentral, and the superior and inferior frontal; the gyri are the anterior central, and the superior, middle, and inferior
frontal. The precentral sulcus runs parallel to the central sulcus, and is usually divided into an upper and a lower part; between it and the central sulcus is the anterior central gyrus. From the precentral sulcus, the superior and inferior frontal
sulci run forward and downward, and divide the remainder of the lateral surface of the lobe into three parallel gyri, named,
respectively the superior, middle, and inferior frontal gyri.
The anterior central gyrus (gyrus centralis anterior; ascending frontal convolution; precentral gyre) is bounded in
front by the precentral sulcus, behind by the central sulcus; it extends from the supero-medial border of the hemisphere to
the posterior ramus of the lateral fissure.
The superior frontal gyrus (gyrus frontalis superior; superfrontal gyre) is situated above the superior frontal sulcus and is continued on to the medial surface of the hemisphere. The portion on the lateral surface of the hemisphere is
usually more or less completely subdivided into an upper and a lower part by an antero-posterior sulcus, the paramedial
sulcus, which, however, is frequently interrupted by bridging gyri.
The middle frontal gyrus (gyrus frontalis medius; medifrontal gyre), between the superior and inferior frontal sulci, is continuous with the anterior orbital gyrus on the inferior surface of the hemisphere; it is frequently subdivided into
two by a horizontal sulcus, the medial frontal sulcus of Eberstaller, which ends anteriorly in a wide bifurcation.
The inferior frontal gyrus (gyrus frontalis inferior; subfrontal gyre) lies below the inferior frontal sulcus, and extends forward from the lower part of the precentral sulcus; it is continuous with the lateral and posterior orbital gyri on the
under surface of the lobe. It is subdivided by the anterior horizontal and ascending rami of the lateral fissure into three
parts, viz., (1) the orbital part, below the anterior horizontal ramus of the fissure; (2) the triangular part (cap of Broca),
between the ascending and horizontal rami; and (3) the basilar part, behind the anterior ascending ramus. The left inferior
frontal gyrus is, as a rule, more highly developed than the right, and is named the gyrus of Broca, from the fact that Broca
described it as the center for articulate speech.
The inferior or orbital surface of the frontal lobe is concave, and rests on the orbital plate of the frontal bone. It is
divided into four orbital gyri by a well-marked H-shaped orbital sulcus. These are named, from their position, the medial,
anterior, lateral, and posterior orbital gyri. The medial orbital gyrus presents a well-marked antero-posterior sulcus, the
olfactory sulcus, for the olfactory tract; the portion medial to this is named the straight gyrus, and is continuous with the
superior frontal gyrus on the medial surface.
The medial surface of the frontal lobe is occupied by the medial part of the superior frontal gyrus (marginal gyrus).
It lies between the cingulate sulcus and the supero-medial margin of the hemisphere. The posterior part of this gyrus is
sometimes marked off by a vertical sulcus, and is distinguished as the paracentral lobule, because it is continuous with the
anterior and posterior central gyri.
Parietal Lobe (lobus parietalis).—The parietal lobe is separated from the frontal lobe by the central sulcus, but its
boundaries below and behind are not so definite. Posteriorly, it is limited by the parietoöccipital fissure, and by a line carried across the hemisphere from the end of this fissure toward the preoccipital notch. Below, it is separated from the temporal lobe by the posterior ramus of the lateral fissure, and by a line carried backward from it to meet the line passing
downward to the preoccipital notch.
The lateral surface of the parietal lobe is cleft by a well-marked furrow, the intraparietal sulcus of Turner, which
consists of an oblique and a horizontal portion. The oblique part is named the postcentral sulcus, and commences below,
about midway between the lower end of the central sulcus and the upturned end of the lateral fissure. It runs upward and
backward, parallel to the central sulcus, and is sometimes divided into an upper and a lower ramus. It forms the hinder limit
of the posterior central gyrus.
From about the middle of the postcentral sulcus, or from the upper end of its inferior ramus, the horizontal portion
of the intraparietal sulcus is carried backward and slightly upward on the parietal lobe, and is prolonged, under the name of
the occipital ramus, on to the occipital lobe, where it divides into two parts, which form nearly a right angle with the main
stem and constitute the transverse occipital sulcus. The part of the parietal lobe above the horizontal portion of the intraparietal sulcus is named the superior parietal lobule; the part below, the inferior parietal lobule.
The posterior central gyrus (gyrus centralis posterior; ascending parietal convolution; postcentral gyre) extends
from the longitudinal fissure above to the posterior ramus of the lateral fissure below. It lies parallel with the anterior central gyrus, with which it is connected below, and also, sometimes, above, the central sulcus.
The superior parietal lobule (lobulus parietalis superior) is bounded in front by the upper part of the postcentral
sulcus, but is usually connected with the posterior central gyrus above the end of the sulcus; behind it is the lateral part of
the parietoöccipital fissure, around the end of which it is joined to the occipital lobe by a curved gyrus, the arcus parietoöccipitalis; below, it is separated from the inferior parietal lobule by the horizontal portion of the intraparietal sulcus.
The inferior parietal lobule (lobulus parietalis inferior; subparietal district or lobule) lies below the horizontal
portion of the intraparietal sulcus, and behind the lower part of the postcentral sulcus. It is divided from before backward
into two gyri. One, the supramarginal, arches over the upturned end of the lateral fissure; it is continuous in front with the
postcentral gyrus, and behind with the superior temporal gyrus. The second, the angular, arches over the posterior end of
the superior temporal sulcus, behind which it is continuous with the middle temporal gyrus.
The medial surface of the parietal lobe is bounded behind by the medial part of the parietoöccipital fissure; in front,
by the posterior end of the cingulate sulcus; and below, it is separated from the cingulate gyrus by the subparietal sulcus.
It is of small size, and consists of a square-shaped convolution, which is termed the precuneus or quadrate lobe.
Occipital Lobe (lobus occipitalis).—The occipital lobe is small and pyramidal in shape; it presents three surfaces:
lateral, medial, and tentorial.
The lateral surface is limited in front by the lateral part of the parietoöccipital fissure, and by a line carried from the
end of this fissure to the preoccipital notch; it is traversed by the transverse occipital and the lateral occipital sulci. The
transverse occipital sulcus is continuous with the posterior end of the occipital ramus of the intraparietal sulcus, and runs
across the upper part of the lobe, a short distance behind the parietoöccipital fissure. The lateral occipital sulcus extends
from behind forward, and divides the lateral surface of the occipital lobe into a superior and an inferior gyrus, which are
continuous in front with the parietal and temporal lobes.
The medial surface of the occipital lobe is bounded in front by the medial part of the parietoöccipital fissure, and is
traversed by the calcarine fissure, which subdivides it into the cuneus and the lingual gyrus. The cuneus is a wedge-shaped
area between the calcarine fissure and the medial part of the parietoöccipital fissure. The lingual gyrus lies between the
calcarine fissure and the posterior part of the collateral fissure; behind, it reaches the occipital pole; in front, it is continued
on to the tentorial surface of the temporal lobe, and joins the hippocampal gyrus.
The tentorial surface of the occipital lobe is limited in front by an imaginary transverse line through the preoccipital notch, and consists of the posterior part of the fusiform gyrus (occipitotemporal convolution) and the lower part of the
lingual gyrus, which are separated from each other by the posterior segment of the collateral fissure.
Temporal Lobe (lobus temporalis).—The temporal lobe presents superior, lateral, and inferior surfaces.
The superior surface forms the lower limit of the lateral fissure and overlaps the insula. On opening out the lateral
fissure, three or four gyri will be seen springing from the depth of the hinder end of the fissure, and running obliquely forward and outward on the posterior part of the upper surface of the superior temporal gyrus; these are named the transverse
temporal gyri (Heschl).
The lateral surface is bounded above by the posterior ramus of the lateral fissure, and by the imaginary line continued backward from it; below, it is limited by the infero-lateral border of the hemisphere. It is divided into superior, middle,
and inferior gyri by the superior and middle temporal sulci. The superior temporal sulcus runs from before backward
across the temporal lobe, some little distance below, but parallel with, the posterior ramus of the lateral fissure; and hence it
is often termed the parallel sulcus. The middle temporal sulcus takes the same direction as the superior, but is situated at
a lower level, and is usually subdivided into two or more parts. The superior temporal gyrus lies between the posterior
ramus of the lateral fissure and the superior temporal sulcus, and is continuous behind with the supramarginal and angular
gyri. The middle temporal gyrus is placed between the superior and middle temporal sulci, and is joined posteriorly with
the angular gyrus. The inferior temporal gyrus is placed below the middle temporal sulcus, and is connected behind with
the inferior occipital gyrus; it also extends around the infero-lateral border on to the inferior surface of the temporal lobe,
where it is limited by the inferior sulcus.
The inferior surface is concave, and is continuous posteriorly with the tentorial surface of the occipital lobe. It is
traversed by the inferior temporal sulcus, which extends from near the occipital pole behind, to within a short distance of
the temporal pole in front, but is frequently subdivided by bridging gyri. Lateral to this fissure is the narrow tentorial part of
the inferior temporal gyrus, and medial to it the fusiform gyrus, which extends from the occipital to the temporal pole; this
gyrus is limited medially by the collateral fissure, which separates it from the lingual gyrus behind and from the hippocampal gyrus in front.
The Insula (island of Reil; central lobe) lies deeply in the lateral or Sylvian fissure, and can only be seen when the
lips of that fissure are widely separated, since it is overlapped and hidden by the gyri which bound the fissure. These gyri
are termed the opercula of the insula; they are separated from each other by the three rami of the lateral fissure, and are
named the orbital, frontal, frontoparietal, and temporal opercula. The orbital operculum lies below the anterior horizontal
ramus of the fissure, the frontal between this and the anterior ascending ramus, the parietal between the anterior ascending
ramus and the upturned end of the posterior ramus, and the temporal below the posterior ramus. The frontal operculum is
of small size in those cases where the anterior horizontal and ascending rami of the lateral fissure arise from a common
stem. The insula is surrounded by a deep circular sulcus which separates it from the frontal, parietal, and temporal lobes.
When the opercula have been removed, the insula is seen as a triangular eminence, the apex of which is directed toward the
anterior perforated substance. It is divided into a larger anterior and a smaller posterior part by a deep sulcus, which runs
backward and upward from the apex of the insula. The anterior part is subdivided by shallow sulci into three or four short
gyri, while the posterior part is formed by one long gyrus, which is often bifurcated at its upper end. The cortical gray substance of the insula is continuous with that of the different opercula, while its deep surface corresponds with the lentiform
nucleus of the corpus striatum.
Limbic Lobe.—The term limbic lobe was introduced by Broca, and under it he included the cingulate and hippocampal gyri, which together arch around the corpus callosum and the hippocampal fissure. These he separated on the morphological ground that they are well-developed in animals possessing a keen sense of smell (osmatic animals), such as the
dog and fox. They were thus regarded as a part of the rhinencephalon, but it is now recognized that they belong to the neopallium; the cingulate gyrus is therefore sometimes described as a part of the frontal lobe, and the hippocampal as a part of
the temporal lobe.
The cingulate gyrus (gyrus cinguli; callosal convolution) is an arch-shaped convolution, lying in close relation to
the superficial surface of the corpus callosum, from which it is separated by a slit-like fissure, the callosal fissure. It commences below the rostrum of the corpus callosum, curves around in front of the genu, extends along the upper surface of
the body, and finally turns downward behind the splenium, where it is connected by a narrow isthmus with the hippocam-
pal gyrus. It is separated from the medial part of the superior frontal gyrus by the cingulate sulcus, and from the precuneus
by the subparietal sulcus.
The hippocampal gyrus (gyrus hippocampi) is bounded above by the hippocampal fissure, and below by the anterior part of the collateral fissure. Behind, it is continuous superiorly, through the isthmus, with the cingulate gyrus and inferiorly with the lingual gyrus. Running in the substance of the cingulate and hippocampal gyri, and connecting them together, is a tract of arched fibers, named the cingulum. The anterior extremity of the hippocampal gyrus is recurved in the form
of a hook (uncus), which is separated from the apex of the temporal lobe by a slight fissure, the incisura temporalis. Although superficially continuous with the hippocampal gyrus, the uncus forms morphologically a part of the rhinencephalon.
The Hippocampal Fissure (fissura hippocampi; dentate fissure) begins immediately behind the splenium of the
corpus callosum, and runs forward between the hippocampal and dentate gyri to end in the uncus. It is a complete fissure
(page 819), and gives rise to the prominence of the hippocampus in the inferior cornu of the lateral ventricle.
The basal ganglions and white matter of the telencephalon
The corpus striatum has received its name from the striped appearance which a section of its anterior part presents,
in consequence of diverging white fibers being mixed with the gray substance which forms its chief mass. A part of the
corpus striatum is imbedded in the white substance of the hemisphere, and is therefore external to the ventricle; it is termed
the extraventricular portion, or the lentiform nucleus; the remainder, however, projects into the ventricle, and is named
the intraventricular portion, or the caudate nucleus.
The caudate nucleus (nucleus caudatus; caudatum) is a pear-shaped, highly arched gray mass; its broad extremity,
or head, is directed forward into the anterior cornu of the lateral ventricle, and is continuous with the anterior perforated
substance and with the anterior end of the lentiform nucleus; its narrow end, or tail, is directed backward on the lateral side
of the thalamus, from which it is separated by the stria terminalis and the terminal vein. It is then continued downward into
the roof of the inferior cornu, and ends in the putamen near the apex of the temporal lobe. It is covered by the lining of the
ventricle, and crossed by some veins of considerable size. It is separated from the lentiform nucleus, in the greater part of
its extent, by a thick lamina of white substance, called the internal capsule, but the two portions of the corpus striatum are
united in front.
The lentiform nucleus (nucleus lentiformis; lenticular nucleus; lenticula) is lateral to the caudate nucleus and thalamus, and is seen only in sections of the hemisphere. When divided horizontally, it exhibits, to some extent, the appearance
of a biconvex lens while a coronal section of its central part presents a somewhat triangular outline. It is shorter than the
caudate nucleus and does not extend as far forward. It is bounded laterally by a lamina of white substance called the external capsule, and lateral to this is a thin layer of gray substance termed the claustrum. Its anterior end is continuous with
the lower part of the head of the caudate nucleus and with the anterior perforated substance.
In a coronal section through the middle of the lentiform nucleus, two medullary laminae are seen dividing it into
three parts. The lateral and largest part is of a reddish color, and is known as the putamen, while the medial and intermediate are of a yellowish tint, and together constitute the globus pallidus; all three are marked by fine radiating white fibers,
which are most distinct in the putamen.
The gray substance of the corpus striatum is traversed by nerve fibers, some of which originate in it. The cells are
multipolar, both large and small; those of the lentiform nucleus contain yellow pigment. The caudate and lentiform nuclei
are not only directly continuous with each other anteriorly, but are connected to each other by numerous fibers. The corpus
striatum is also connected: (1) to the cerebral cortex, by what are termed the corticostriate fibers; (2) to the thalamus, by
fibers which pass through the internal capsule, and by a strand named the ansa lentiformis; (3) to the cerebral peduncle, by
fibers which leave the lower aspect of the caudate and lentiform nuclei.
The claustrum is a thin layer of gray substance, situated on the lateral surface of the external capsule. Its transverse
section is triangular, with the apex directed upward. Its medial surface, contiguous to the external capsule, is smooth, but its
lateral surface presents ridges and furrows corresponding with the gyri and sulci of the insula, with which it is in close relationship. The claustrum is regarded as a detached portion of the gray substance of the insula, from which it is separated by a
layer of white fibers, the capsula extrema (band of Baillarger). Its cells are small and spindle-shaped, and contain yellow
pigment; they are similar to those of the deepest layer of the cortex.
The nucleus amygdalae (amygdala) is an ovoid gray mass, situated at the lower end of the roof of the inferior cornu. It is merely a localized thickening of the gray cortex, continuous with that of the uncus; in front it is continuous with the
putamen, behind with the stria terminalis and the tail of the caudate nucleus.
The internal capsule (capsula interna) is a flattened band of white fibers, between the lentiform nucleus on the lateral side and the caudate nucleus and thalamus on the medial side. In horizontal section it is seen to be somewhat abruptly
curved, with its convexity inward; the prominence of the curve is called the genu, and projects between the caudate nucleus
and the thalamus. The portion in front of the genu is termed the frontal part, and separates the lentiform from the caudate
nucleus; the portion behind the genu is the occipital part, and separates the lentiform nucleus from the thalamus.
The frontal part of the internal capsule contains: (1) fibers running from the thalamus to the frontal lobe; (2) fibers
connecting the lentiform and caudate nuclei; (3) fibers connecting the cortex with the corpus striatum; and (4) fibers passing from the frontal lobe through the medial fifth of the base of the cerebral peduncle to the nuclei pontis. The fibers in the
region of the genu are named the geniculate fibers; they originate in the motor part of the cerebral cortex, and, after passing downward through the base of the cerebral peduncle with the cerebrospinal fibers, undergo decussation and end in the
motor nuclei of the cranial nerves of the opposite side. The anterior two-thirds of the occipital part of the internal capsule
contains the cerebrospinal fibers, which arise in the motor area of the cerebral cortex and, passing downward through the
middle three-fifths of the base of the cerebral peduncle, are continued into the pyramids of the medulla oblongata. The posterior third of the occipital part contains: (1) sensory fibers, largely derived from the thalamus, though some may be continued upward from the medial lemniscus; (2) the fibers of optic radiation, from the lower visual centers to the cortex of the
occipital lobe; (3) acoustic fibers, from the lateral lemniscus to the temporal lobe; and (4) fibers which pass from the occipital and temporal lobes to the nuclei pontis.
The fibers of the internal capsule radiate widely as they pass to and from the various parts of the cerebral cortex,
forming the corona radiata and intermingling with the fibers of the corpus callosum.
The external capsule (capsula externa) is a lamina of white substance, situated lateral to the lentiform nucleus, between it and the claustrum, and continuous with the internal capsule below and behind the lentiform nucleus. It probably
contains fibers derived from the thalamus, the anterior commissure, and the subthalamic region.
The substantia innominata of Meynert is a stratum consisting partly of gray and partly of white substance, which
lies below the anterior part of the thalamus and lentiform nucleus. It consists of three layers, superior, middle, and inferior.
The superior layer is named the ansa lentiformis, and its fibers, derived from the medullary lamina of the lentiform nucleus, pass medially to end in the thalamus and subthalamic region, while others are said to end in the tegmentum and red nucleus. The middle layer consists of nerve cells and nerve fibers; fibers enter it from the parietal lobe through the external
capsule, while others are said to connect it with the medial longitudinal fasciculus. The inferior layer forms the main part of
the inferior stalk of the thalamus, and connects this body with the temporal lobe and the insula.
The stria terminalis (taenia semicircularis) is a narrow band of white substance situated in the depression between
the caudate nucleus and the thalamus. Anteriorly, its fibers are partly continued into the column of the fornix; some, however, pass over the anterior commissure to the gray substance between the caudate nucleus and septum pellucidum, while
others are said to enter the caudate nucleus. Posteriorly, it is continued into the roof of the inferior cornu of the lateral ventricle, at the extremity of which it enters the nucleus amygdalae. Superficial to it is a large vein, the terminal vein (vein of
the corpus striatum), which receives numerous tributaries from the corpus striatum and thalamus; it runs forward to the
interventricular foramen and there joins with the vein of the choroid plexus to form the corresponding internal cerebral
vein. On the surface of the terminal vein is a narrow white band, named the lamina affixa.
The Lateral Ventricles (ventriculus lateralis).—The two lateral ventricles are irregular cavities situated in the lower and medial parts of the cerebral hemispheres, one on either side of the middle line. They are separated from each other
by a median vertical partition, the septum pellucidum, but communicate with the third ventricle and indirectly with each
other through the interventricular foramen. They are lined by a thin, diaphanous membrane, the ependyma, covered by
ciliated epithelium, and contain cerebrospinal fluid, which, even in health, may be secreted in considerable amount. Each
lateral ventricle consists of a central part or body, and three prolongations from it, termed cornua.
The central part (pars centralis ventriculi lateralis; cella) of the lateral ventricle extends from the interventricular
foramen to the splenium of the corpus callosum. It is an irregularly curved cavity, triangular on transverse section, with a
roof, a floor, and a medial wall. The roof is formed by the under surface of the corpus callosum; the floor by the following
parts, enumerated in their order of position, from before backward: the caudate nucleus of the corpus striatum, the stria
terminalis and the terminal vein, the lateral portion of the upper surface of the thalamus, the choroid plexus, and the lateral
part of the fornix; the medial wall is the posterior part of the septum pellucidum, which separates it from the opposite ventricle.
The anterior cornu (cornu anterius; anterior horn; precornu) passes forward and lateralward, with a slight inclination downward, from the interventricular foramen into the frontal lobe, curving around the anterior end of the caudate nucleus. Its floor is formed by the upper surface of the reflected portion of the corpus callosum, the rostrum. It is bounded
medially by the anterior portion of the septum pellucidum, and laterally by the head of the caudate nucleus. Its apex reaches
the posterior surface of the genu of the corpus callosum.
The posterior cornu (cornu posterius; postcornu) passes into the occipital lobe, its direction being backward and
lateralward, and then medialward. Its roof is formed by the fibers of the corpus callosum passing to the temporal and occipital lobes. On its medial wall is a longitudinal eminence, the calcar avis (hippocampus minor), which is an involution of
the ventricular wall produced by the calcarine fissure. Above this the forceps posterior of the corpus callosum, sweeping
around to enter the occipital lobe, causes another projection, termed the bulb of the posterior cornu. The calcar avis and
bulb of the posterior cornu are extremely variable in their degree of development; in some cases they are ill-defined, in others prominent.
The inferior cornu (cornu inferior; descending horn; middle horn; medicornu) the largest of the three, traverses the
temporal lobe of the brain, forming in its course a curve around the posterior end of the thalamus. It passes at first backward, lateralward, and downward, and then curves forward to within 2.5 cm. of the apex of the temporal lobe, its direction
being fairly well indicated on the surface of the brain by that of the superior temporal sulcus. Its roof is formed chiefly by
the inferior surface of the tapetum of the corpus callosum, but the tail of the caudate nucleus and the stria terminalis also
extend forward in the roof of the inferior cornu to its extremity; the tail of the caudate nucleus joins the putamen. Its floor
presents the following parts: the hippocampus, the fimbria hippocampi, the collateral eminence, and the choroid plexus.
When the choroid plexus is removed, a cleft-like opening is left along the medial wall of the inferior cornu; this cleft constitutes the lower part of the choroidal fissure.
Practice skills
Students are supposed to identify the following structures on the samples and schemas:
Cerebral hemisphere
- temporal lobe
- longitudinal cerebral fissure
- occipital lobe
- lateral fossa
- insular lobe
- frontal lobe
Superolateral surface of cerebral hemi- parietal lobe
sphere
- central sulcus
- lateral sulcus
frontal lobe
- frontal pole
- precentral sulcus
- precentral gyrus
- superior frontal sulcus
- inferior frontal sulcus
- superior frontal gyrus
- middle frontal gyrus
- inferior frontal gyrus
- ascending ramus
- anterior ramus
- opercular part
- triangular part
- orbital part
parietal lobe
- postcentral sulcus
- postcentral gyrus
- superior parietal lobule
- intraparietal sulcus
- inferior parietal lobule
- angular gyrus
- supramarginal gyrus
temporal lobe
- superior temporal sulcus
- inferior temporal sulcus
- superior temporal gyrus
- middle temporal gyrus
- inferior temporal gyrus
- transverse temporal gyri
occipital lobe
- occipital pole
insula
- insular gyri
Medial and inferior surfaces of cerebral
hemispheres
- sulcus of corpus callosum
- cingulate sulcus
- cingulated gyrus
- isthmus of cingulated gyrus
- hippocampal sulcus
- hippocampal gyrus
- uncus
- dentate gyrus
- rhinal sulcus
- paracentral sulcus
- paracentral lobule
- precuneus
- parietooccipital sulcus
- cuneus
- calcarine sulcus
- lingual gyrus
- collateral sulcus
- medial occipitotemporal gyrus
- occipitotemporal sulcus
- lateral occipitotemporal gyrus
- straight gyrus
- olfactory sulcus
- orbital sulci
- orbital gyri
corpus callosum
- rostrum
- genu
- trunk
- splenium
- septum pellucidum
fornix
- column
- body
- crus
- olfactory bulb
- olfactory tract
- olfactory trigone
- anterior perforated substance
Basal nuclei
- corpus striatum
- caudate nucleus
- head
- body
- tail
- lentiform nucleus
- putamen
- lateral globus pallidus
- medial globus pallidus
- claustrum
Lateral ventricles
- central part of the lateral ventricle
- the walls of the central part
- anterior (frontal) horn
- the walls of the anterior horn
- posterior (occipital) horn
- the walls of the posterior horn
- calcar avis
- collateral eminence
- inferior (temporal) horn
- the walls of the inferior horn
- hippocampus
- interventricular foramen
- external capsule
- internal capsule
- anterior limb of internal capsule
- genu of internal capsule
- posterior limb of internal capsule
Self-taught class 1. The midbrain.
The aim: to learn the structure and topography of the midbrain.
Professional orientation: the knowledge of this topic is necessary for doctors of all the specialities; it
represents special interest for therapists, neurologists and neuropathologists.
The plan of the self-taught class:
A.
B.
C.
D.
E.
F.
Learn the structures composing the midbrain.
Find out the structures of the midbrain seen on the dorsal and ventral aspects of the brainstem.
Learn the peculiarities of the internal structure of the midbrain.
Find out the localization of the cranial nerves nuclei in the midbrain.
Learn the projection of the cranial nerves nuclei on the dorsal surface of the brainstem.
Learn the conductive tracts on the level of the midbrain.
The mid-brain or mesencephalon is the short, constricted portion which connects the pons and cerebellum with the
thalamencephalon and cerebral hemispheres. It is directed upward and forward, and consists of (1) a ventrolateral portion,
composed of a pair of cylindrical bodies, named the cerebral peduncles; (2) a dorsal portion, consisting of four rounded
eminences, named the corpora quadrigemina; and (3) an intervening passage or tunnel, the cerebral aqueduct, which
represents the original cavity of the mid-brain and connects the third with the fourth ventricle.
The cerebral peduncles (pedunculus cerebri; crus cerebri) are two cylindrical masses situated at the base of the
brain, and largely hidden by the temporal lobes of the cerebrum, which must be drawn aside or removed in order to expose
them. They emerge from the upper surface of the pons, one on either side of the middle line, and, diverging as they pass
upward and forward, disappear into the substance of the cerebral hemispheres. The depressed area between the crura is
termed the interpeduncular fossa, and consists of a layer of grayish substance, the posterior perforated substance,
which is pierced by small apertures for the transmission of bloodvessels; its lower part lies on the ventral aspect of the medial portions of the tegmenta, and contains a nucleus named the interpeduncular ganglion; its upper part assists in forming the floor of the third ventricle. The ventral surface of each peduncle is crossed from the medial to the lateral side by the
superior cerebellar and posterior cerebral arteries; its lateral surface is in relation to the gyrus hippocampi of the cerebral
hemisphere and is crossed from behind forward by the trochlear nerve. Close to the point of disappearance of the peduncle
into the cerebral hemisphere, the optic tract winds forward around its ventro-lateral surface. The medial surface of the peduncle forms the lateral boundary of the interpeduncular fossa, and is marked by a longitudinal furrow, the oculomotor
sulcus, from which the roots of the oculomotor nerve emerge. On the lateral surface of each peduncle there is a second longitudinal furrow, termed the lateral sulcus; the fibers of the lateral lemniscus come to the surface in this sulcus, and pass
backward and upward, to disappear under the inferior colliculus.
Structure of the Cerebral Peduncles.—On transverse section, each peduncle is seen to consist of a dorsal and a
ventral part, separated by a deeply pigmented lamina of gray substance, termed the substantia nigra. The dorsal part is
named the tegmentum; the ventral, the base or crusta; the two bases are separated from each other, but the tegmenta are
joined in the median plane by a forward prolongation of the raphé of the pons. Laterally, the tegmenta are free; dorsally,
they blend with the corpora quadrigemina.
The base (basis pedunculi; crusta or pes) is semilunar on transverse section, and consists almost entirely of longitudinal bundles of efferent fibers, which arise from the cells of the cerebral cortex and are grouped into three principal sets,
viz., cerebrospinal, frontopontine, and temporopontine. The cerebrospinal fibers, derived from the cells of the motor area
of the cerebral cortex, occupy the middle three-fifths of the base; they are continued partly to the nuclei of the motor cranial
nerves, but mainly into the pyramids of the medulla oblongata. The frontopontine fibers are situated in the medial fifth of
the base; they arise from the cells of the frontal lobe and end in the nuclei of the pons. The temporopontine fibers are lateral to the cerebrospinal fibers; they originate in the temporal lobe and end in the nuclei pontis.
The substantia nigra (intercalatum) is a layer of gray substance containing numerous deeply pigmented, multipolar
nerve cells. It is semilunar on transverse section, its concavity being directed toward the tegmentum; from its convexity,
prolongations extend between the fibers of the base of the peduncle. Thicker medially than laterally, it reaches from the
oculomotor sulcus to the lateral sulcus, and extends from the upper surface of the pons to the subthalamic region; its medial
part is traversed by the fibers of the oculomotor nerve as these stream forward to reach the oculomotor sulcus. The connections of the cells of the substantia nigra have not been definitely established. It receives collaterals from the medial lemniscus and the pyramidal bundles. Bechterew is of the opinion that the fibers from the motor area of the cerebral cortex form
synapses with cells whose axons pass to the motor nucleus of the trigeminal nerve and serve for the coördination of the
muscles of mastication.
The tegmentum is continuous below with the reticular formation of the pons, and, like it, consists of longitudinal
and transverse fibers, together with a considerable amount of gray substance. The principal gray masses of the tegmentum
are the red nucleus and the interpeduncular ganglion; of its fibers the chief longitudinal tracts are the superior peduncle, the
medial longitudinal fasciculus, and the lemniscus.
GRAY SUBSTANCE.—The red nucleus is situated in the anterior part of the tegmentum, and is continued upward
into the posterior part of the subthalamic region. In sections at the level of the superior colliculus it appears as a circular
mass which is traversed by the fibers of the oculomotor nerve. It receives many terminals and collaterals from the superior
cerebellar peduncle also collaterals from the ventral longitudinal bundle, from Gudden’s bundle and the median lemniscus.
The axons of its larger cells cross the middle line and are continued downward into the lateral funiculus of the medulla spinalis as the rubrospinal tract; those of its smaller cells end mainly in the thalamus. The rubrospinal tract forms an important
part of the pathway from the cerebellum to the lower motor centers.
The interpeduncular ganglion is a median collection of nerve cells situated in the ventral part of the tegmentum.
The fibers of the fasciculus retroflexus of Meynert, which have their origin in the cells of the ganglion habenulae, end in it.
Besides the two nuclei mentioned, there are small collections of cells which form the dorsal and ventral nuclei and
the central nucleus or nucleus of the raphé.
WHITE SUBSTANCE.—(1) The origin and course of the superior peduncle have already been described.
(2) The medial (posterior) longitudinal fasciculus is continuous below with the proper fasciculi of the anterior and
lateral funiculi of the medulla spinalis. In the medulla oblongata and pons it runs close to the middle line, near the floor of
the fourth ventricle; in the mid-brain it is situated on the ventral aspect of the cerebral aqueduct, below the nuclei of the
oculomotor and trochlear nerves. Its connections are imperfectly known, but it consists largely of ascending and descending
intersegmental or association fibers, which connect the nuclei of the hind-brain and mid-brain to each other. Many of the
fibers arise in Deiters’s nucleus (lateral vestibular nucleus) and divide into ascending and descending branches which send
terminals and collaterals to the motor nuclei of the cranial and spinal nerves. Its spinal portion is located in the anterior funiculus and is known as the vestibulospinal fasciculus. Other fibers pass to the median longitudinal bundle from cells in
the reticular formation of the medulla, pons and mid-brain and also from certain large cells in the terminal nucleus of the
trigeminal nerve. According to Edinger it extends to the so-called nucleus of the posterior longitudinal bundle in the hypothalamic region, but this is uncertain and the fibers above the nucleus of the oculomotor are smaller in diameter than the
rest of the bundle. According to Held fibers from the posterior commissure can be traced into the posterior longitudinal
bundle, and according to the same author many of the descending fibers arise in the superior colliculus, and, after decussating in the middle line, end in the motor nuclei of the pons and medulla oblongata. These fibers from the superior colliculus
probably pass into the ventral longitudinal bundle. Fibers are said to pass through the medial longitudinal fasciculus from
the nucleus of the abducent nerve into the oculomotor nerve of the opposite side, and through this nerve to the Rectus medialis oculi. Fraser, however, denies the existence of such fibers. Again, fibers are said to be prolonged through this fasciculus from the nucleus of the oculomotor nerve into the facial nerve, and are distributed to the Orbicularis oculi, the Corrugator, and the Frontalis.
The ventral longitudinal bundle consists for the most part of the tectospinal fasciculus, and arises from the superior colliculus, the fibers arch ventrally around the central gray matter and cross the midline in the fountain-decussation of
Meynert. They then descend in the tegmentum, part of them passing through the red nucleus ventral to the medial longitudinal bundle. In the medulla oblongata and spinal cord its fibers are more or less intermingled with the medial longitudinal
bundle and the rubrospinal tract. It descends in the adjoining region of the ventral and lateral funiculi. Collaterals and terminals are given off to the red nucleus and probably other nuclei of the brain stem and to the anterior column of the spinal
cord. It is probably concerned in optic reflexes.
(3) The medial lemniscus or medial fillet.—The fibers of the medial lemniscus take origin in the gracile and cuneate nuclei of the medulla oblongata, and as internal arcuate fibers they cross to the opposite side in the sensory decussation.
They then pass in the interolivary stratum upward through the medulla oblongata, in which they are situated behind the
cerebrospinal fibers and between the olives. In the pons and lower part of the mid-brain it occupies the ventral part of the
reticular formation and tegmentum close to the raphé, while above it gradually shifts to the dorso-lateral part of the tegmentum in the angle between the red nucleus and the substantia nigra. In the pons it assumes a flattened ribbon-like appearance,
and is placed dorsal to the trapezium. As the lemniscus ascends, it receives additional fibers from the terminal sensory nuclei of the cranial nerves of the opposite side. Many of the fibers which arise from the terminal sensory nuclei of the cranial
nerves pass upward in the formatio reticularis as a separate bundle, known as the central tract of the cranial nerves, to the
thalamus.
Many fibers either terminate in or send off collaterals to the gray matter of the medulla, the pons, and the mid-brain.
Large numbers of fibers pass to or from the substantia nigra. Many collaterals enter the red nucleus and other fibers are said
to run to the superior colliculus. The great bulk of the fibers, however, enter the ventro-lateral portion of the thalamus, give
off collaterals to the posterior semilunar nucleus and then terminate in the principal sensory nucleus of the thalamus.
In the cerebral peduncle, a few of its fibers pass upward in the lateral part of the base of the peduncle, on the dorsal
aspect of the temporopontine fibers, and reach the lentiform nucleus and the insula. The greater part of the medial lemniscus, on the other hand, is prolonged through the tegmentum, and most of its fibers end in the thalamus; probably some are
continued directly through the occipital part of the internal capsule to the cerebral cortex. From the cells of the thalamus a
relay of fibers is prolonged to the cerebral cortex.
The medial lemniscus may be considered as the upward continuation of the posterior funiculus of the spinal cord
and to convey conscious impulses of muscle sense and tactile discrimination.
The central or thalamic tract of the cranial nerves is closely associated with the medial lemniscus. The fibers of
the spinothalamic fasciculi are continued from the spinal cord into this tract which passes upward in the reticular formation
and the tegmentum to the thalamus along the dorsal side of the median lemniscus. It receives fibers from the opposite terminal sensory nuclei of the vagus, glossopharyngeal, facial, trigeminal and probably the vestibular nerves. Many of the
secondary sensory fibers of the trigeminal cross the raphé from its terminal nucleus and pass upward to the thalamus by a
more or less separate but closely associated pathway known as the central tract of the trigeminal nerve which also lies on
the dorsal aspect of the lemniscus. These two tracts give off collaterals to the posterior semilunar nucleus of the thalamus
and terminate in the anterior semilunar nucleus of the ventro-lateral region of the thalamus sending collaterals into the zona
incerta.
The fibers of the rubrospinal tract (bundle of Monakow) arise in the red nucleus, cross the midline in the decussation of Forel and pass downward in the formatio reticularis of the brainstem into the lateral funiculus of the spinal cord ventral to the crossed pyramidal tract.
The lateral lemniscus (lemniscus lateralis) comes to the surface of the mid-brain along its lateral sulcus, and disappears under the inferior colliculus. It consists of fibers from the terminal nuclei of the cochlear division of the acoustic
nerve, together with others from the superior olivary and trapezoid nuclei. Most of these fibers are crossed, but some are
uncrossed. Many of them pass to the inferior colliculus of the same or opposite side, but others are prolonged to the thalamus, and thence through the occipital part of the internal capsule to the middle and superior temporal gyri.
The corpora quadrigemina are four rounded eminences which form the dorsal part of the mid-brain. They are situated above and in front of the anterior medullary velum and superior peduncle, and below and behind the third ventricle
and posterior commissure. They are covered by the splenium of the corpus callosum, and are partly overlapped on either
side by the medial angle, or pulvinar, of the posterior end of the thalamus; on the lateral aspect, under cover of the pulvinar, is an oval eminence, named the medial geniculate body. The corpora quadrigemina are arranged in pairs (superior
and inferior colliculi), and are separated from one another by a crucial sulcus. The longitudinal part of this sulcus expands
superiorly to form a slight depression which supports the pineal body, a cone-like structure which projects backward from
the thalamencephalon and partly obscures the superior colliculi. From the inferior end of the longitudinal sulcus, a white
band, termed the frenulum veli, is prolonged downward to the anterior medullary velum; on either side of this band the
trochlear nerve emerges, and passes forward on the lateral aspect of the cerebral peduncle to reach the base of the brain.
The superior colliculi are larger and darker in color than the inferior, and are oval in shape. The inferior colliculi are hemispherical, and somewhat more prominent than the superior. The superior colliculi are associated with the sense of sight,
the inferior with that of hearing.
From the lateral aspect of each colliculus a white band, termed the brachium, is prolonged upward and forward.
The superior brachium extends lateralward from the superior colliculus, and, passing between the pulvinar and medial
geniculate body, is partly continued into an eminence called the lateral geniculate body, and partly into the optic tract. The
inferior brachium passes forward and upward from the inferior colliculus and disappears under cover of the medial geniculate body.
In close relationship with the corpora quadrigemina are the superior peduncles, which emerge from the upper and
medial parts of the cerebellar hemispheres. They run upward and forward, and, passing under the inferior colliculi, enter the
tegmenta as already described.
Structure of the Corpora Quadrigemina.—The inferior colliculus (colliculus inferior; inferior quadrigeminal
body; postgemina) consists of a compact nucleus of gray substance containing large and small multipolar nerve cells, and
more or less completely surrounded by white fibers derived from the lateral lemniscus. Most of these fibers end in the gray
nucleus of the same side, but some cross the middle line and end in that of the opposite side. From the cells of the gray nucleus, fibers are prolonged through the inferior brachium into the tegmentum of the cerebral peduncle, and are carried to the
thalamus and the cortex of the temporal lobe; other fibers cross the middle line and end in the opposite colliculus.
The superior colliculus (colliculus superior; superior quadrigeminal body; pregemina) is covered by a thin stratum
(stratum zonale) of white fibers, the majority of which are derived from the optic tract. Beneath this is the stratum cinereum, a cap-like layer of gray substance, thicker in the center than at the circumference, and consisting of numerous small
multipolar nerve cells, imbedded in a fine network of nerve fibers. Still deeper is the stratum opticum, containing large
multipolar nerve cells, separated by numerous fine nerve fibers. Finally, there is the stratum lemnisci, consisting of fibers
derived partly from the lemniscus and partly from the cells of the stratum opticum; interspersed among these fibers are
many large multipolar nerve cells. The two last-named strata are sometimes termed the gray-white layers, from the fact
that they consist of both gray and white substance. Of the afferent fibers which reach the superior colliculus, some are derived from the lemniscus, but the majority have their origins in the retina and are conveyed to it through the superior brachium; all of them end by arborizing around the cells of the gray substance. Of the efferent fibers, some cross the middle
line to the opposite colliculus; many ascend through the superior brachium, and finally reach the cortex of the occipital lobe
of the cerebrum; while others, after undergoing decussation (fountain decussation of Meynert) form the tectospinal fasciculus which descends through the formatio reticularis of the midbrain, pons, and medulla oblongata into the medulla spinalis, where it is found partly in the anterior funiculus and partly intermingled with the fibers of the rubrospinal tract.
The corpora quadrigemina are larger in the lower animals than in man. In fishes, reptiles, and birds they are hollow,
and only two in number (corpora bigemina); they represent the superior colliculi of mammals, and are frequently termed
the optic lobes, because of their intimate connection with the optic tracts.
The cerebral aqueduct (aqueductus cerebri; aqueduct of Sylvius) is a narrow canal, about 15 mm. long, situated between the corpora quadrigemina and tegmenta, and connecting the third with the fourth ventricle. Its shape, as seen in
transverse section, varies at different levels, being T-shaped, triangular above, and oval in the middle; the central part is
slightly dilated, and was named by Retzius the ventricle of the mid-brain. It is lined by ciliated columnar epithelium, and
is surrounded by a layer of gray substance named the central gray stratum: this is continuous below with the gray substance in the rhomboid fossa, and above with that of the third ventricle. Dorsally, it is partly separated from the gray substance of the quadrigeminal bodies by the fibers of the lemniscus; ventral to it are the medial longitudinal fasciculus, and
the formatio reticularis of the tegmentum. Scattered throughout the central gray stratum are numerous nerve cells of various
sizes, interlaced, by a net-work of fine fibers. Besides these scattered cells it contains three groups which constitute the nuclei of the oculomotor and trochlear nerves, and the nucleus of the mesencephalic root of the trigeminal nerve. The nucleus
of the trigeminal nerve extends along the entire length of the aqueduct, and occupies the lateral part of the gray stratum,
while the nuclei of the oculomotor and trochlear nerves are situated in its ventral part. The nucleus of the oculomotor
nerve is about 10 cm. long, and lies under the superior colliculus, beyond which, however, it extends for a short distance
into the gray substance of the third ventricle. The nucleus of the trochlear nerve is small and nearly circular, and is on a
level with a plane carried transversely through the upper part of the inferior colliculus.
Note. A band of fibers, the tractus peduncularis transversus, is sometimes seen emerging from in front of the superior colliculus; it passes around the ventral aspect of the peduncle about midway between the pons and the optic tract, and
dips into the oculomotor sulcus. This band is a constant structure in many mammals, but is only present in about 30 per
cent. of human brains. Since it undergoes atrophy after enucleation of the eyeballs, it may be considered as forming a path
for visual sensations.
The fibers of the rubrospinal tract (bundle of Monakow) arise in the red nucleus, cross the midline in the decussation of Forel and pass downward in the formatio reticularis of the brainstem into the lateral funiculus of the spinal cord ventral to the crossed pyramidal tract.
The lateral lemniscus (lemniscus lateralis) comes to the surface of the mid-brain along its lateral sulcus, and disappears under the inferior colliculus. It consists of fibers from the terminal nuclei of the cochlear division of the acoustic
nerve, together with others from the superior olivary and trapezoid nuclei. Most of these fibers are crossed, but some are
uncrossed. Many of them pass to the inferior colliculus of the same or opposite side, but others are prolonged to the thalamus, and thence through the occipital part of the internal capsule to the middle and superior temporal gyri.
The corpora quadrigemina are four rounded eminences which form the dorsal part of the mid-brain. They are situated above and in front of the anterior medullary velum and superior peduncle, and below and behind the third ventricle
and posterior commissure. They are covered by the splenium of the corpus callosum, and are partly overlapped on either
side by the medial angle, or pulvinar, of the posterior end of the thalamus; on the lateral aspect, under cover of the pulvinar, is an oval eminence, named the medial geniculate body. The corpora quadrigemina are arranged in pairs (superior
and inferior colliculi), and are separated from one another by a crucial sulcus. The longitudinal part of this sulcus expands
superiorly to form a slight depression which supports the pineal body, a cone-like structure which projects backward from
the thalamencephalon and partly obscures the superior colliculi. From the inferior end of the longitudinal sulcus, a white
band, termed the frenulum veli, is prolonged downward to the anterior medullary velum; on either side of this band the
trochlear nerve emerges, and passes forward on the lateral aspect of the cerebral peduncle to reach the base of the brain.
The superior colliculi are larger and darker in color than the inferior, and are oval in shape. The inferior colliculi are hemispherical, and somewhat more prominent than the superior. The superior colliculi are associated with the sense of sight,
the inferior with that of hearing.
From the lateral aspect of each colliculus a white band, termed the brachium, is prolonged upward and forward.
The superior brachium extends lateralward from the superior colliculus, and, passing between the pulvinar and medial
geniculate body, is partly continued into an eminence called the lateral geniculate body, and partly into the optic tract. The
inferior brachium passes forward and upward from the inferior colliculus and disappears under cover of the medial geniculate body.
In close relationship with the corpora quadrigemina are the superior peduncles, which emerge from the upper and
medial parts of the cerebellar hemispheres. They run upward and forward, and, passing under the inferior colliculi, enter the
tegmenta as already described.
Practice skills
Students are supposed to identify the following structures on the samples and schemas:
Midbrain
- interpeduncular fossa
- tectum of midbrain
- posterior perforated substance
- tectal (quadrigeminal) plate
- cerebral peduncle
- superior colliculus
- tegmentum of midbrain
- inferior colliculus
- red nucleus
- brachium of superior colliculus
- substantia nigra
- brachium of inferior colliculus
- base of peduncle
- cerebral aqueduct
Self-taught class 2. The “olfactory” brain. The structure of the cortex.
The aim: to learn the structure and topography of the “olfactory brain” (rhinencephalon); to find out the
dynamic localization of functions in the cerebral cortex.
Professional orientation: the knowledge of this topic is necessary for doctors of all the specialities; it
represents special interest for therapists, neurologists and neuropathologists.
The plan of the self-taught class:
A. Learn the composition and localization of the telencepalon structures, united in the notion of the
“olfactory brain”.
B. Find the structures of the “olfactory brain” on the schemas and samples.
C. Find out the anatomical and functional significance of the “olfactory brain”.
D. Learn the general structure of the cerebral cortex and its peculiarities in different regions of the
hemispheres relative to the functions of the cortex.
E. Learn the localization of the main cortical centers (nuclei) of analyzers relative to the gyri and lobes
of the cerebral hemispheres.
F. Make a schema of grooves and gyri of the cerebral hemispheres and mark the areas of dynamic localization of functions in the cerebral cortex with different colors.
Rhinencephalon—The rhinencephalon comprises the olfactory lobe, the uncus, the subcallosal and supracallosal
gyri, the fascia dentata hippocampi, the septum pellucidum, the fornix, and the hippocampus.
1. The Olfactory Lobe (lobus olfactorius) is situated under the inferior or orbital surface of the frontal lobe. In many
vertebrates it constitutes a well-marked portion of the hemisphere and contains an extension of the lateral ventricle; but in
man and some other mammals it is rudimentary. It consists of the olfactory bulb and tract, the olfactory trigone, the parolfactory area of Broca, and the anterior perforated substance.
(a) The olfactory bulb (bulbus olfactorius) is an oval, reddish-gray mass which rests on the cribriform plate of the
ethmoid and forms the anterior expanded extremity of the olfactory tract. Its under surface receives the olfactory nerves,
which pass upward through the cribriform plate from the olfactory region of the nasal cavity.
(b) The olfactory tract (tractus olfactorius) is a narrow white band, triangular on coronal section, the apex being directed upward. It lies in the olfactory sulcus on the inferior surface of the frontal lobe, and divides posteriorly into two striae, a medial and a lateral. The lateral stria is directed across the lateral part of the anterior perforated substance and then
bends abruptly medialward toward the uncus of the hippocampal gyrus. The medial stria turns medialward behind the parolfactory area and ends in the subcallosal gyrus; in some cases a small intermediate stria is seen running backward to the
anterior perforated substance.
(c) The olfactory trigone (trigonum olfactorium) is a small triangular area in front of the anterior perforated substance. Its apex, directed forward, occupies the posterior part of the olfactory sulcus, and is brought into view by throwing
back the olfactory tract.
(d) The parolfactory area of Broca (area parolfactoria) is a small triangular field on the medial surface of the hemisphere in front of the subcallosal gyrus, from which it is separated by the posterior parolfactory sulcus; it is continuous below with the olfactory trigone, and above and in front with the cingulate gyrus; it is limited anteriorly by the anterior parolfactory sulcus.
(e) The anterior perforated substance (substantia perforata anterior) is an irregularly quadrilateral area in front of
the optic tract and behind the olfactory trigone, from which it is separated by the fissure prima; medially and in front it is
continuous with the subcallosal gyrus; laterally it is bounded by the lateral stria of the olfactory tract and is continued into
the uncus. Its gray substance is confluent above with that of the corpus striatum, and is perforated anteriorly by numerous
small bloodvessels.
2. The Uncus - the recurved, hook-like portion of the hippocampal gyrus.
3. The Subcallosal, Supracallosal, and Dentate Gyri form a rudimentary arch-shaped lamina of gray substance extending over the corpus callosum and above the hippocampal gyrus from the anterior perforated substance to the uncus.
(a) The subcallosal gyrus (gyrus subcallosus; peduncle of the corpus callosum) is a narrow lamina on the medial
surface of the hemisphere in front of the lamina terminalis, behind the parolfactory area, and below the rostrum of the corpus callosum. It is continuous around the genu of the corpus callosum with the supracallosal gyrus.
(b) The supracallosal gyrus (indusium griseum; gyrus epicallosus) consists of a thin layer of gray substance in contact with the upper surface of the corpus callosum and continuous laterally with the gray substance of the cingulate gyrus. It
contains two longitudinally directed strands of fibers termed respectively the medial and lateral longitudinal striae. The
supracallosal gyrus is prolonged around the splenium of the corpus callosum as a delicate lamina, the fasciola cinerea,
which is continuous below with the fascia dentata hippocampi.
(c) The fascia dentata hippocampi (gyrus dentatus) is a narrow band extending downward and forward above the
hippocampal gyrus but separated from it by the hippocampal fissure; its free margin is notched and overlapped by the fimbria—the fimbriodentate fissure intervening. Anteriorly it is continued into the notch of the uncus, where it forms a sharp
bend and is then prolonged as a delicate band, the band of Giacomini, over the uncus, on the lateral surface of which it is
lost.
Structure of the Cerebral Cortex - The cerebral cortex differs in thickness and structure in different parts of the
hemisphere. It is thinner in the occipital region than in the anterior and posterior central gyri, and it is also much thinner at
the bottom of the sulci than on the top of the gyri. Again, the minute structure of the anterior central differs from that of the
posterior central gyrus, and areas possessing a specialized type of cortex can be mapped out in the occipital lobe.
On examining a section of the cortex with a lens, it is seen to consist of alternating white and gray layers thus disposed from the surface inward: (1) a thin layer of white substance; (2) a layer of gray substance; (3) a second white layer
(outer band of Baillarger or band of Gennari); (4) a second gray layer; (5) a third white layer (inner band of Baillarger);
(6) a third gray layer, which rests on the medullary substance of the gyrus.
The cortex is made up of nerve cells of varying size and shape, and of nerve fibers which are either medullated or
naked axis-cylinders, imbedded in a matrix of neuroglia.
Nerve Cells.—According to Cajal, the nerve cells are arranged in four layers, named from the surface inward as follows: (1) the molecular layer, (2) the layer of small pyramidal cells, (3) the layer of large pyramidal cells, (4) the layer of
polymorphous cells.
The Molecular Layer.—In this layer the cells are polygonal, triangular, or fusiform in shape. Each polygonal cell
gives off some four or five dendrites, while its axon may arise directly from the cell or from one of its dendrites. Each triangular cell gives off two or three dendrites, from one of which the axon arises. The fusiform cells are placed with their
long axes parallel to the surface and are mostly bipolar, each pole being prolonged into a dendrite, which runs horizontally
for some distance and furnishes ascending branches. Their axons, two or three in number, arise from the dendrites, and, like
them, take a horizontal course, giving off numerous ascending collaterals. The distribution of the axons and dendrites of all
three sets of cells is limited to the molecular layer.
The Layer of Small and the Layer of Large Pyramidal Cells.—The cells in these two layers may be studied together,
since, with the exception of the difference in size and the more superficial position of the smaller cells, they resemble each
other. The average length of the small cells is from 10 to 15μ; that of the large cells from 20 to 30μ. The body of each cell
is pyramidal in shape, its base being directed to the deeper parts and its apex toward the surface. It contains granular pigment, and stains deeply with ordinary reagents. The nucleus is of large size, and round or oval in shape. The base of the cell
gives off the axis cylinder, and this runs into the central white substance, giving off collaterals in its course, and is distributed as a projection, commissural, or association fiber. The apical and basal parts of the cell give off dendrites; the apical
dendrite is directed toward the surface, and ends in the molecular layer by dividing into numerous branches, all of which
may be seen, when prepared by the silver or methylene-blue method, to be studded with projecting bristle-like processes.
The largest pyramidal cells are found in the upper part of the anterior central gyrus and in the paracentral lobule; they are
often arranged in groups or nests of from three to five, and are named the giant cells of Betz. In the former situation they
may exceed 50μ in length and 40μ in breadth, while in the paracentral lobule they may attain a length of 65μ.
Layer of Polymorphous Cells.—The cells in this layer, as their name implies, are very irregular in contour; they may
be fusiform, oval, triangular, or star-shaped. Their dendrites are directed outward, but do not reach so far as the molecular
layer; their axons pass into the subjacent white matter.
There are two other kinds of cells in the cerebral cortex. They are: (a) the cells of Golgi, the axons of which divide
immediately after their origins into a large number of branches, which are directed toward the surface of the cortex; (b) the
cells of Martinotti, which are chiefly found in the polymorphous layer; their dendrites are short, and may have an ascending
or descending course, while their axons pass out into the molecular layer and form an extensive horizontal arborization.
Nerve Fibers.—These fill up a large part of the intervals between the cells, and may be medullated or nonmedullated—the latter comprising the axons of the smallest pyramidal cells and the cells of Golgi. In their direction the
fibers may be either tangential or radial. The tangential fibers run parallel to the surface of the hemisphere, intersecting the
radial fibers at a right angle. They constitute several strata, of which the following are the more important: (1) a stratum of
white fibers covering the superficial aspect of the molecular layer (plexus of Exner); (2) the band of Bechterew, in the outer
part of the layer of small pyramidal cells; (3) the band of Gennari or external band of Baillarger, running through the layer
of large pyramidal cells; (4) the internal band of Baillarger, between the layer of large pyramidal cells and the polymorphous layer; (5) the deep tangential fibers, in the lower part of the polymorphous layer. The tangential fibers consist of (a)
the collaterals of the pyramidal and polymorphous cells and of the cells of Martinotti; (b) the branching axons of Golgi’s
cells; (c) the collaterals and terminal arborizations of the projection, commissural, or association fibers. The radial fibers.—
Some of these, viz., the axons of the pyramidal and polymorphous cells, descend into the central white matter, while others,
the terminations of the projection, commissural, or association fibers, ascend to end in the cortex. The axons of the cells of
Martinotti are also ascending fibers.
Special Types of Cerebral Cortex.—It has been already pointed out that the minute structure of the cortex differs
in different regions of the hemisphere; and A. W. Campbell has endeavored to prove, as the result of an exhaustive examination of a series of human and anthropoid brains, “that there exists a direct correlation between physiological function and
histological structure.” The principal regions where the “typical” structure is departed from will now be referred to.
1. In the calcarine fissure and the gyri bounding it, the internal band of Baillarger is absent, while the band of Gennari is of considerable thickness, and forms a characteristic feature of this region of the cortex. If a section be examined microscopically, an additional layer of cells is seen to be interpolated between the molecular layer and the layer of small pyramidal cells. This extra layer consists of two or three strata of fusiform cells, the long axes of which are at right angles to
the surface; each cell gives off two dendrites, external and internal, from the latter of which the axon arises and passes into
the white central substance. In the layer of small pyramidal cells, fusiform cells, identical with the above, are seen, as well
as ovoid or star-like cells with ascending axons (cells of Martinotti). This is the visual area of the cortex, and it has been
shown by J. S. Bolton that in old-standing cases of optic atrophy the thickness of Gennari’s band is reduced by nearly 50
per cent.
A. W. Campbell says: “Histologically, two distinct types of cortex can be made out in the occipital lobe. The first of
these coats the walls and bounding convolutions of the calcarine fissure, and is distinguished by the well-known line of
Gennari or Vicq d’Azyr; the second area forms an investing zone a centimetre or more broad around the first, and is characterized by a remarkable wealth of fibers, as well as by curious pyriform cells of large size richly stocked with chromophilic
elements—cells which seem to have escaped the observation of Ramón y Cajal, Bolton, and others who have worked at this
region. As to the functions of these two regions there is abundant evidence, anatomical, embryological, and pathological, to
show that the first or calcarine area is that to which visual sensations primarily pass, and we are gradually obtaining proof
to the effect that the second investing area is constituted for the interpretation and further elaboration of these sensations.
These areas therefore deserve the names visuo-sensory and visuo-psychic.”
2. The anterior central gyrus is characterized by the presence of the giant cells of Betz and by “a wealth of nerve fibers immeasurably superior to that of any other part” (Campbell), and in these respects differs from the posterior central
gyrus. These two gyri, together with the paracentral lobule, were long regarded as constituting the “motor areas” of the
hemisphere; but Sherrington and Grunbaum have shown that in the chimpanzee the motor area never extends on to the free
face of the posterior central gyrus, but occupies the entire length of the anterior central gyrus, and in most cases the greater
part or the whole of its width. It extends into the depth of the central sulcus, occupying the anterior wall, and in some places
the floor, and in some extending even into the deeper part of the posterior wall of the sulcus.
3. In the hippocampus the molecular layer is very thick and contains a large number of Golgi cells. It has been divided into three strata: (a) s. convolutum or s. granulosum, containing many tangential fibers; (b) s. lacunosum, presenting
numerous vascular spaces; (c) s. radiatum, exhibiting a rich plexus of fibrils. The two layers of pyramidal cells are condensed into one, and the cells are mostly of large size. The axons of the cells in the polymorphous layer may run in an ascending, a descending, or a horizontal direction. Between the polymorphous layer and the ventricular ependyma is the
white substance of the alveus.
4. In the fascia dentata hippocampi or dentate gyrus the molecular layer contains some pyramidal cells, while the
layer of pyramidal cells is almost entirely represented by small ovoid cells.
5. The Olfactory Bulb.—In many of the lower animals this contains a cavity which communicates through the olfactory tract with the lateral ventricle. In man the original cavity is filled up by neuroglia and its wall becomes thickened, but
much more so on its ventral than on its dorsal aspect. Its dorsal part contains a small amount of gray and white substance,
but it is scanty and ill-defined. A section through the ventral part shows it to consist of the following layers from without
inward:
1. A layer of olfactory nerve fibers, which are the non-medullated axons prolonged from the olfactory cells of the
nasal cavity, and reach the bulb by passing through the cribriform plate of the ethmoid bone. At first they cover the bulb,
and then penetrate it to end by forming synapses with the dendrites of the mitral cells, presently to be described.
2. Glomerular Layer.—This contains numerous spheroidal reticulated enlargements, termed glomeruli, produced by
the branching and arborization of the processes of the olfactory nerve fibres with the descending dendrites of the mitral
cells.
3. Molecular Layer.—This is formed of a matrix of neuroglia, imbedded in which are the mitral cells. These cells are
pyramidal in shape, and the basal part of each gives off a thick dendrite which descends into the glomerular layer, where it
arborizes as indicated above, and others which interlace with similar dendrites of neighboring mitral cells. The axons pass
through the next layer into the white matter of the bulb, and after becoming bent on themselves at a right angle, are continued into the olfactory tract.
4. Nerve Fiber Layer.—This lies next the central core of neuroglia, and its fibers consist of the axons or afferent processes of the mitral cells passing to the brain; some efferent fibers are, however, also present, and end in the molecular layer, but nothing is known as to their exact origin.
Cerebral Localization.—Physiological and pathological research have now gone far to prove that a considerable
part of the surface of the brain may be mapped out into a series of more or less definite areas, each of which is intimately
connected with some well-defined function.
Motor Areas.—The motor area occupies the anterior central and frontal gyri and the paracentral lobule. The centers
for the lower limb are located on the uppermost part of the anterior central gyrus and its continuation on to the paracentral
lobule; those for the trunk are on the upper portion, and those for the upper limb on the middle portion of the anterior central gyrus. The facial centers are situated on the lower part of the anterior central gyrus, those for the tongue, larynx, muscles of mastication, and pharynx on the frontal operculum, while those for the head and neck occupy the posterior end of
the middle frontal gyrus.
Sensory Areas.—Tactile and temperature senses are located on the posterior central gyrus, while the sense of form
and solidity is on the superior parietal lobule and precuneus. With regard to the special senses, the area for the sense of taste
is probably related to the uncus and hippocampal gyrus. The auditory area occupies the middle third of the superior temporal gyrus and the adjacent gyri in the lateral fissure; the visual area, the calcarine fissure and cuneus; the olfactory area,
the rhinencephalon. As special centers of much importance may be noted: the emissive center for speech on the left inferior
frontal and anterior central gyri (Broca); the auditory receptive center on the transverse and superior temporal gyri, and the
visual receptive center on the lingual gyrus and cuneus.
Practice skills
See the list of practical skills for practice class 4 (The anatomy of forebrain: the grooves and gyri. The basal ganglions and white matter of the forebrain. The lateral ventricles).
Self-taught class 3. The meninges and spaces of the brain. The cerebrospinal fluid and
pathway of its circulation.
The aim: to learn the structure, anatomic and functional significance of the meninges of the brain (dura
mater, arachnoid mater and pia mater), the derivates of these meninges and the spaces between the cerebral meninges; to understand the production and the pathways of circulation of the cerebrospinal fluid in the cavities of
the brain and in the subarachnoid spaces of the brain and the spinal cord.
Professional orientation: the knowledge of this topic is necessary for doctors of all the specialities; it
represents special interest for therapists, neurologists, neuropathologists, neurosurgeons, psychiatrists, traumatologists.
The plan of the self-taught class:
A. Learn the structure, localization and the derivates of the meninges of the brain.
B. Find out the role of the dura mater in formation of the venous sinuses - the pathways of circulation of
the venous blood in the cavity of the skull.
C. Learn the localization of the reserve spaces of the subarachnoid space – the cisterns. Find out their
role in accumulation and circulation of the cerebrospinal fluid.
D. Make a schema of circulation of the cerebrospinal fluid and a schema of circulation of the venous
blood in the sinuses of the cranial dura mater.
The brain and medulla spinalis are enclosed within three membranes. These are named from without inward: the dura mater, the arachnoid, and the pia mater.
The dura mater is a thick and dense inelastic membrane. The portion which encloses the brain differs in several essential particulars from that which surrounds the medulla spinalis, and therefore it is necessary to describe them separately;
but at the same time it must be distinctly understood that the two form one complete membrane, and are continuous with
each other at the foramen magnum.
The Cranial Dura Mater (dura mater encephali; dura of the brain) lines the interior of the skull, and serves the
twofold purpose of an internal periosteum to the bones, and a membrane for the protection of the brain. It is composed of
two layers, an inner or meningeal and an outer or endosteal, closely connected together, except in certain situations, where,
as already described (page 654), they separate to form sinuses for the passage of venous blood. Its outer surface is rough
and fibrillated, and adheres closely to the inner surfaces of the bones, the adhesions being most marked opposite the sutures
and at the base of the skull its inner surface is smooth and lined by a layer of endothelium. It sends inward four processes
which divide the cavity of the skull into a series of freely communicating compartments, for the lodgement and protection
of the different parts of the brain; and it is prolonged to the outer surface of the skull, through the various foramina which
exist at the base, and thus becomes continuous with the pericranium; its fibrous layer forms sheaths for the nerves which
pass through these apertures. Around the margin of the foramen magnum it is closely adherent to the bone, and is continuous with the spinal dura mater.
Processes.—The processes of the cranial dura mater, which projects into the cavity of the skull, are formed by reduplications of the inner or meningeal layer of the membrane, and are four in number: the falx cerebri, the tentorium cerebelli, the falx cerebelli, and the diaphragma sellae.
The falx cerebri so named from its sickle-like form, is a strong, arched process which descends vertically in the longitudinal fissure between the cerebral hemispheres. It is narrow in front, where it is attached to the crista galli of the ethmoid; and broad behind, where it is connected with the upper surface of the tentorium cerebelli. Its upper margin is convex,
and attached to the inner surface of the skull in the middle line, as far back as the internal occipital protuberance; it contains
the superior sagittal sinus. Its lower margin is free and concave, and contains the inferior sagittal sinus.
The tentorium cerebelli is an arched lamina, elevated in the middle, and inclining downward toward the circumference. It covers the superior surface of the cerebellum, and supports the occipital lobes of the brain. Its anterior border is free
and concave, and bounds a large oval opening, the incisura tentorii, for the transmission of the cerebral peduncles. It is
attached, behind, by its convex border, to the transverse ridges upon the inner surface of the occipital bone, and there encloses the transverse sinuses; in front, to the superior angle of the petrous part of the temporal bone on either side, enclosing the superior petrosal sinuses. At the apex of the petrous part of the temporal bone the free and attached borders meet,
and, crossing one another, are continued forward to be fixed to the anterior and posterior clinoid processes respectively. To
the middle line of its upper surface the posterior border of the falx cerebri is attached, the straight sinus being placed at
their line of junction.
The falx cerebelli is a small triangular process of dura mater, received into the posterior cerebellar notch. Its base is
attached, above, to the under and back part of the tentorium; its posterior margin, to the lower division of the vertical crest
on the inner surface of the occipital bone. As it descends, it sometimes divides into two smaller folds, which are lost on the
sides of the foramen magnum.
The diaphragma sellae is a small circular horizontal fold, which roofs in the sella turcica and almost completely covers the hypophysis; a small central opening transmits the infundibulum.
Structure.—The cranial dura mater consists of white fibrous tissue and elastic fibers arranged in flattened laminae
which are imperfectly separated by lacunar spaces and bloodvessels into two layers, endosteal and meningeal. The endosteal layer is the internal periosteum for the cranial bones, and contains the bloodvessels for their supply. At the margin of the
foramen magnum it is continuous with the periosteum lining the vertebral canal. The meningeal or supporting layer is lined
on its inner surface by a layer of nucleated flattened mesothelium, similar to that found on serous membranes.
The arteries of the dura mater are very numerous. Those in the anterior fossa are the anterior meningeal branches of
the anterior and posterior ethmoidal and internal carotid, and a branch from the middle meningeal. Those in the middle fossa are the middle and accessory meningeal of the internal maxillary; a branch from the ascending pharyngeal, which enters
the skull through the foramen lacerum; branches from the internal carotid, and a recurrent branch from the lacrimal. Those
in the posterior fossa are meningeal branches from the occipital, one entering the skull through the jugular foramen, and
another through the mastoid foramen; the posterior meningeal from the vertebral; occasional meningeal branches from the
ascending pharyngeal, entering the skull through the jugular foramen and hypoglossal canal; and a branch from the middle
meningeal.
The veins returning the blood from the cranial dura mater anastomose with the diploic veins and end in the various
sinuses. Many of the meningeal veins do not open directly into the sinuses, but indirectly through a series of ampullae,
termed venous lacunae. These are found on either side of the superior sagittal sinus, especially near its middle portion, and
are often invaginated by arachnoid granulations; they also exist near the transverse and straight sinuses. They communicate
with the underlying cerebral veins, and also with the diploic and emissary veins.
The nerves of the cranial dura mater are filaments from the semilunar ganglion, from the ophthalmic, maxillary,
mandibular, vagus, and hypoglossal nerves, and from the sympathetic.
The arachnoid is a delicate membrane enveloping the brain and medulla spinalis and lying between the pia mater
internally and the dura mater externally; it is separated from the pia mater by the subarachnoid cavity, which is filled with
cerebrospinal fluid.
The Cranial Part (arachnoidea encephali) of the arachnoid invests the brain loosely, and does not dip into the sulci
between the gyri, nor into the fissures, with the exception of the longitudinal. On the upper surface of the brain the arachnoid is thin and transparent; at the base it is thicker, and slightly opaque toward the central part, where it extends across
between the two temporal lobes in front of the pons, so as to leave a considerable interval between it and the brain.
Structure.—The arachnoid consists of bundles of white fibrous and elastic tissue intimately blended together. Its
outer surface is covered with a layer of low cuboidal mesothelium. The inner surface and the trabeculae are likewise covered by a somewhat low type of cuboidal mesothelium which in places are flattened to a pavement type. Vessels of considerable size, but few in number, and, according to Bochdalek, a rich plexus of nerves derived from the motor root of the trigeminal, the facial, and the accessory nerves, are found in the arachnoid.
The Subarachnoid Cavity (cavum subarachnoideale; subarachnoid space) is the interval between the arachnoid and
pia mater. It is occupied by a spongy tissue consisting of trabeculae of delicate connective tissue, and intercommunicating
channels in which the subarachnoid fluid is contained. This cavity is small on the surface of the hemispheres of the brain;
on the summit of each gyrus the pia mater and the arachnoid are in close contact; but in the sulci between the gyri, triangular spaces are left, in which the subarachnoid trabecular tissue is found, for the pia mater dips into the sulci, whereas the
arachnoid bridges across them from gyrus to gyrus. At certain parts of the base of the brain, the arachnoid is separated from
the pia mater by wide intervals, which communicate freely with each other and are named subarachnoid cisternae; in these
the subarachnoid tissue is less abundant.
Subarachnoid Cisternae (cisternae subarachnoidales)—The cisterna cerebellomedullaris (cisterna magna) is triangular on sagittal section, and results from the arachnoid bridging over the interval between the medulla oblongata and the under surfaces of the hemispheres of the cerebellum; it is continuous with the subarachnoid cavity of the medulla spinalis at
the level of the foramen magnum. The cisterna pontis is a considerable space on the ventral aspect of the pons. It contains
the basilar artery, and is continuous behind with the subarachnoid cavity of the medulla spinalis, and with the cisterna cerebellomedullaris; and in front of the pons with the cisterna interpeduncularis. The cisterna interpeduncularis (cisterna basalis) is a wide cavity where the arachnoid extends across between the two temporal lobes. It encloses the cerebral peduncles
and the structures contained in the interpeduncular fossa, and contains the arterial circle of Willis. In front, the cisterna interpeduncularis extends forward across the optic chiasma, forming the cisterna chiasmatis, and on to the upper surface of
the corpus callosum, for the arachnoid stretches across from one cerebral hemisphere to the other immediately beneath the
free border of the falx cerebri, and thus leaves a space in which the anterior cerebral arteries are contained. The cisterna
fossae cerebri lateralis is formed in front of either temporal lobe by the arachnoid bridging across the lateral fissure. This
cavity contains the middle cerebral artery. The cisterna venae magnae cerebri occupies the interval between the splenium of
the corpus callosum and the superior surface of the cerebellum; it extends between the layers of the tela chorioidea of the
third ventricle and contains the great cerebral vein.
The subarachnoid cavity communicates with the general ventricular cavity of the brain by three openings; one, the
foramen of Majendie, is in the middle line at the inferior part of the roof of the fourth ventricle; the other two are at the extremities of the lateral recesses of that ventricle, behind the upper roots of the glossopharyngeal nerves and are known as
the foramina of Luschka. It is still somewhat uncertain whether these foramina are actual openings or merely modified areas of the inferior velum which permit the passage of the cerebrospinal fluid from the ventricle into the subarachnoid spaces
as through a permeable membrane.
The spinal part of the subarachnoid cavity is a very wide interval, and is the largest at the lower part of the vertebral
canal, where the arachnoid encloses the nerves which form the cauda equina. Above, it is continuous with the cranial subarachnoid cavity; below, it ends at the level of the lower border of the second sacral vertebra. It is partially divided by a
longitudinal septum, the subarachnoid septum, which connects the arachnoid with the pia mater opposite the posterior median sulcus of the medulla spinalis, and forms a partition, incomplete and cribriform above, but more perfect in the thoracic
region. The spinal subarachnoid cavity is further subdivided by the ligamentum denticulatum, which will be described with
the pia mater.
The Arachnoid Villi (granulationes arachnoideales; glandulae Pacchioni; Pacchionian bodies) are small, fleshylooking elevations, usually collected into clusters of variable size, which are present upon the outer surface of the dura mater, in the vicinity of the superior sagittal sinus, and in some other situations. Upon laying open the sagittal sinus and the
venous lacunae on either side of it villi will be found protruding into its interior. They are not seen in infancy, and very
rarely until the third year. They are usually found after the seventh year; and from this period they increase in number and
size as age advances. They are not glandular in structure, but are enlarged normal villi of the arachnoid. As they grow they
push the thinned dura mater before them, and cause absorption of the bone from pressure, and so produce the pits or depressions on the inner wall of the calvarium.
Structure.—An arachnoidal villus represents an invasion of the dura by the arachnoid membrane, the latter penetrates the dura in such a manner that the arachnoid mesothelial cells come to lie directly beneath the vascular endothelium
of the great dural sinuses. It consists of the following parts: (1) In the interior is a core of subarachnoid tissue, continuous
with the meshwork of the general subarachnoid tissue through a narrow pedicle, by which the villus is attached to the
arachnoid. (2) Around this tissue is a layer of arachnoid membrane, limiting and enclosing the subarachnoid tissue. (3) Outside this is the thinned wall of the lacuna, which is separated from the arachnoid by a potential space which corresponds to
and is continuous with the subdural cavity. (4) And finally, if the villus projects into the sagittal sinus, it will be covered by
the greatly thinned wall of the sinus which may consist merely of endothelium. It will be seen, therefore, that fluid injected
into the subarachnoid cavity will find its way into these villi, and it has been found experimentally that it passes from the
villi into the venous sinuses into which they project.
The Pia Mater—The pia mater is a vascular membrane, consisting of a minute plexus of bloodvessels, held together by an extremely fine areolar tissue and covered by a reflexion of the mesothelial cells from the arachnoid trabeculae. It is
an incomplete membrane, absent probably at the foramen of Majendie and the two foramina of Luschka and perforated in a
peculiar manner by all the bloodvessels as they enter or leave the nervous system. In the perivascular spaces, the pia apparently enters as a mesothelial lining of the outer surface of the space; a variable distance from the exterior these cells become unrecognizable and are apparently lacking, replaced by neuroglia elements. The inner walls of these perivascular
spaces seem likewise covered for a certain distance by the mesothelial cells, reflected with the vessels from the arachnoid
covering of these vascular channels as they traverse the subarachnoid spaces.
The Cranial Pia Mater (pia mater encephali; pia of the brain) invests the entire surface of the brain, dips between
the cerebral gyri and cerebellar laminae, and is invaginated to form the tela chorioidea of the third ventricle, and the choroid plexuses of the lateral and third ventricles (pages 840 and 841); as it passes over the roof of the fourth ventricle, it
forms the tela chorioidea and the choroid plexuses of this ventricle. On the cerebellum the membrane is more delicate; the
vessels from its deep surface are shorter, and its relations to the cortex are not so intimate.
The cerebrospinal fluid, for the most part elaborated by the choroid plexuses, is poured into the cerebral ventricles
which are lined by smooth ependyma. That portion of the fluid formed in the lateral ventricles escapes by the foramen of
Monro into the third ventricle and thence by the aqueduct into the fourth ventricle. Likewise an ascending current of fluid
apparently occurs in the central canal of the spinal cord; this, representing a possible product of the ependyma, may be added to the intraventricular supply. From the fourth ventricle the fluid is poured into the subarachnoid spaces through the medial foramen of Majendie and the two lateral foramina of Luschka. There is no evidence that functional communications
between the cerebral ventricles and the subarachnoid spaces exist in any region except from the fourth ventricle.
In addition to the elaboration of the cerebrospinal fluid by the choroid plexuses, there seems fairly well established a
second source of the fluid from the nervous system itself. The bloodvessels that enter and leave the brain are surrounded by
perivascular channels. It seems most likely that the outer wall of these channels is lined by a continuation inward of the pial
mesothelium while the inner wall is probably derived from the mesothelial covering of the vessels, which are thus protected
throughout the subarachnoid spaces. These mesothelial cells continue inward only a short distance, neuroglia cells probably
replacing on the outer surface the mesothelial elements. Through these perivascular channels there is probably a small
amount of fluid flowing from nerve-cell to subarachnoid space. The chemical differences between the subarachnoid fluid
(product of choroid plexuses and perivascular system) and the ventricular fluid (product of choroid plexuses alone) indicate
that the products of nerve-metabolism are poured into the subarachnoid space.
The absorption of the cerebrospinal fluid is a dual process, being chiefly a rapid drainage through the arachnoid villi
into the great dural sinuses, and, in small part, a slow escape into the true lymphatic vessels, by way of an abundant but
indirect perineural course.
In general the arachnoid channels are equipped as fluid retainers with unquestionable powers of diffusion or absorption in regard to certain elements in the normal cerebrospinal fluid, deriving in this way a cellular nutrition.
The subdural space (between arachnoid and dura) is usually considered to be a part of the cerebrospinal channels. It
is a very small space, the two limiting surfaces being separated by merely a capillary layer of fluid. Whether this fluid is
exactly similar to the cerebrospinal fluid is very difficult to ascertain. Likewise our knowledge of the connections between
the subdural and subarachnoid spaces is hardly definite. In some ways the subdural space may be likened to a serous cavity.
The inner surface of the dura is covered by flattened polygonal mesothelial cells but the outer surface of the arachnoid is
covered by somewhat cuboidal mesothelium. The fluid of the subdural space has probably a local origin from the cells lining it.
Practice skills
Students are supposed to identify the following structures on the schemas and samples:
Spinal dura mater
- occipital sinus
Cranial dura mater
- transverse sinus
- falx cerebri
- confluence of sinuses
- falx cerebelli
- sigmoid sinus
- tentorium cerebelli
- cavernous sinus
- diaphragma sellae
- superior petrosal sinus
dural venous sinuses
- inferior petrosal sinus
- superior sagittal sinus
Cranial arachnoid mater
- inferior sagittal sinus
Spinal arachnoid mater
- straight sinus
Cranial pia mater
Spinal pia mater
Self-taught class 4. The conducting tracts of the brain and spinal cord. The afferent conducting tracts. The efferent conducting tracts.
The aim: to learn the principles of structure of the white substance of brain and spinal cord, the division
of white substance fibers into the commissural, association and projection fibers; to learn the division of the projection fibers into ascending and descending conducting tracts; to find out the anatomic and functional significance and general principles of structure and communication of projection tracts of brain and spinal cord.
Professional orientation: the knowledge of this topic is necessary for doctors of all the specialities to understand the development of stages of pathogenesis in clinical practice.
The plan of the self-taught class:
A. Learn the general principles of white substance fibers structure, their division, anatomical and functional significance.
B. Learn the direction of the projection fibers and the connections between different parts of the spinal
cord, brainstem and the forebrain.
C. Find out the division of the ascending projection tracts into exteroceptive, proprioceptive and interoceptive according to localization of receptors. Learn the general principles and peculiarities of interneuron connections of ascending conducting tracts.
D. Find out the division of the descending tracts into the main motor (pyramidal) and the group of extrapyramidal tracts. Learn the general principles, anatomic and functional significance of descending
conducting tracts.
E. Make the schemas of main ascending and descending projection tracts.
The fibers arise either from cortical nerve cells or terminate on them: there are three different fiber systems: projection fibers, association fibers and commissural fibers. Projection fibers connect the cerebral cortex with the subcortical centers, either as ascending systems which end in the cortex, or as descending systems which extend from the cerebral cortex
to the deeper centers. Association fibers connect the various parts of the cortex to each other and commissural fibers connect the cortex of the two hemispheres: they are really only interhemispherical association fibers.
Projection fibers. Descending tracts which arise from the diverse cortical regions combine in a fan-shape to form the
internal capsule. The ascending fibers pass through the internal capsule and radiate outward, also in a fanshape. Thus, subcortical ascending and descending fibers form a fanlike fiber mass beneath the cortex, called the corona radiata.
In a horizontal section, the internal capsule forms an angle which has an anterior limb, limited by the head of the
caudate nucleus, the pallidum and the putamen, and a posterior limb, which is delimited by the thalamus, the pallidum and
the putamen. The genu of the Internal capsule lies between the two limbs The various fiber tracts pass through specific
parts of the internal capsule. The frontopontine tract and the anterior thalamic peduncle pass through the anterior limb. Corticonuclear fibers lie in the region of the genu of the internal capsule. The fibers of the corticospinal tract adjoin it in the
posterior limb in a somatotopic arrangement of arm, trunk and leg. The thalamocortical fibers to area 4 run through the
same region, and so do the corticorubro- and corticotegmental fibers which stem from area 6. The caudal part of the posterior limb is occupied by fibers from the dorsal thalamic peduncle, which run through to the postcentral region. Fibers of the
posterior thalamic peduncle and the temporopontine tract run obliquely through its caudal end.
The auditory and visual radiations are amongst the most important projection tracts. The fibers of the auditory radiation anse from the medial geniculate body, extend over the lateral geniculate body, and at the lower margin of the putamen they cross the internal capsule. They ascend almost vertically in the white matter of the temporal lobe to the anterior
transverse gyrus. The visual radiation arises from the lateral geniculate body and its fibers fan out to form a wide myelin
lamella. They extend into the temporal lobes where they form the temporal genu of the visual tract. They then run in an arc
around the inferior horn of the lateral ventricle and pass through the white matter of the occipital lobe to the calcarine sulcus. Corpus callosum, cerebral peduncle.
Association fibers. The connections between the diverse cortical areas are of very different lengths. To simplify, we
distinguish short and long association fibers. The short association fibers, arcuate fibers, provide connection within one
cerebral lobe, or from one convolution to the next. The shortest fibers connect adjacent parts of the cortex; after running a
short course in the white matter they re-enter the cortex. They are called U-fibers. The layer of U-fibers lies directly beneath the cortical layer.
The long association fibers connect the various lobes of the brain and form macroscopically demonstrable, discrete
tracts. The cingulum is a large system of shorter and longer fibers which follows the cingulate gyrus throughout its entire
length. The long fibers extend between the parolfactory region, beneath the rostrum of the corpus callosum and the entorhinal region. The subcallosal fasciculus lies dorsolateral to the caudate nucleus, beneath the radiation of the corpus callosum.
Its fibers connect the frontal lobes with the temporal and occipital lobes. Some of the fibers pass to the region of the insula
and others connect the frontal lobes to the caudate nucleus. The superior longitudinal fasciculus, which lies dorsolateral to
the putamen, is a large association tract between the frontal and occipital lobes, and fibers pass from it to the parietal and
temporal lobes. The inferior fronto-occipital fasciculus, from the frontal lobes to the occipital lobes, passes through the
ventral part of the extreme capsule. The inferior longitudinal fasciculus extends between the occipital and temporal lobes
The uncinate fasciculus connects the temporal and frontal cortex. Its ventral part forms a connection between the entorhinal
cortex and the orbital cortex of the frontal lobes. Other fiber tracts are the vertical occipital fasciculus and the orbitofrontal
fasciculus.
Commissural fibers. Interhemispheric association fibers pass through the corpus callosum, the rostral commissure
and the commissure of the fornix to the contralateral hemisphere The most important commissure of the neocortex is the
corpus callosum. Its curved oral part is called the genu of the corpus callosum with the pointed rostrum at the anterior tip.
There follows the middle part, the body, and the thickened posterior end, the splenium. The fibers of the corpus callosum
spread through the white matter of both hemispheres and form the radiation of the corpus callosum. The fibers which run
through the genu of the corpus callosum and join the two frontal lobes are called the forceps minor whilst those which pass
through the splenium and join the two occipital lobes are called the forceps mayor.
We distinguish homotopic and heterotopic interhemispheric fibers. Homotopic fibers connect the same cortical regions in troth hemispheres and heterotopic fibers connect different areas. The majority of callosal fibers are homotopic. Not
all cortical areas are interconnected to the same extent with the corresponding area in the contralateral hemisphere. The
areas concerned with the hand and foot in both somatosensory regions, for example, have no interhemispheric fiber connections The two visual cortices are also not joined to each other. Many fiber connections, on the other hand, exist between the
two areas 18.
The descending fasciculi which convey impulses from the higher centers to the spinal cord and located in the lateral
and ventral funiculi.
The Motor Tract conveying voluntary impulses, arises from the pyramid cells situated in the motor area of the cortex, the anterior central and the posterior portions of the frontal gyri and the paracentral lobule. The fibers are at first
somewhat widely diffused, but as they descend through the corona radiata they gradually approach each other, and pass
between the lentiform nucleus and thalamus, in the genu and anterior two-thirds of the occipital part of the internal capsule;
those in the genu are named the geniculate fibers, while the remainder constitute the cerebrospinal fibers; proceeding
downward they enter the middle three-fifths of the base of the cerebral peduncle. The geniculate fibers cross the middle
line, and end by arborizing around the cells of the motor nuclei of the cranial nerves. The cerebrospinal fibers are continued downward into the pyramids of the medulla oblongata, and the transit of the fibers from the medulla oblongata is effected by two paths. The fibers nearest to the anterior median fissure cross the middle line, forming the decussation of the
pyramids, and descend in the opposite side of the medulla spinalis, as the lateral cerebrospinal fasciculus (crossed pyramidal tract). Throughout the length of the medulla spinalis fibers from this column pass into the gray substance, to terminate either directly or indirectly around the motor cells of the anterior column. The more laterally placed portion of the
tract does not decussate in the medulla oblongata, but descends as the anterior cerebrospinal fasciculus (direct pyramidal
tract); these fibers, however, end in the anterior gray column of the opposite side of the medulla spinalis by passing across
in the anterior white commissure. There is considerable variation in the extent to which decussation takes place in the medulla oblongata; about two-thirds or three-fourths of the fibers usually decussate in the medulla oblongata and the remainder in the medulla spinalis.
The axons of the motor cells in the anterior column pass out as the fibers of the anterior roots of the spinal nerves,
along which the impulses are conducted to the muscles of the trunk and limbs.
From this it will be seen that all the fibers of the motor tract pass to the nuclei of the motor nerves on the opposite
side of the brain or medulla spinalis, a fact which explains why a lesion involving the motor area of one side causes paralysis of the muscles of the opposite side of the body. Further, it will be seen that there is a break in the continuity of the motor
chain; in the case of the cranial nerves this break occurs in the nuclei of these nerves; and in the case of the spinal nerves, in
the anterior gray column of the medulla spinalis. For clinical purposes it is convenient to emphasize this break and divide
the motor tract into two portions: (1) a series of upper motor neurons which comprises the motor cells in the cortex and
their descending fibers down to the nuclei of the motor nerves; (2) a series of lower motor neurons which includes the
cells of the nuclei of the motor cerebral nerves or the cells of the anterior columns of the medulla spinalis and their axiscylinder processes to the periphery.
The rubrospinal fasciculus arises from the large cells of the red nucleus. The fibers cross the raphé of the mid-brain
in the decussation of Forel and descend in the formatio reticularis of the pons and medulla dorsal to the medial lemniscus
and as they pass into the spinal cord come to lie in a position ventral to the crossed pyramidal tracts in the lateral funiculus.
The rubrospinal fibers end either directly or indirectly by terminals and collaterals about the motor cells in the anterior column on the side opposite from their origin in the red nucleus. A few are said to pass down on the same side. Since the red
nucleus is intimately related to the cerebellum by terminals and collaterals of the superior peduncle which arises in the dentate nucleus of the cerebellum, the rubrospinal fasciculus is supposed to be concerned with cerebellar reflexes, complex
motor coördinations necessary in locomotion and equilibrium. The afferent paths concerned in these reflexes have already
been partly considered, namely, the dorsal and ventral spinocerebellar fasciculi, and probably some of the fibers of the posterior funiculi which reach the cerebellum by the inferior peduncle.
The tectospinal fasciculus arises from the superior colliculus of the roof (tectum) of the mid-brain. The axons come
from large cells in the stratum opticum and stratum lemnisci and sweep ventrally around the central gray matter of the aqueduct, cross the raphé in the fountain decussation of Meynert and turn downward in the tegmentum in the ventral longitudinal bundle. Some of the fibers do not cross in the raphé but pass down on the same side; it is uncertain whether they come
from the superior colliculus of the same side or arch over the aqueduct from the colliculus of the opposite side. The tectospinal fasciculus which comprises the major part of the ventral longitudinal bundle passes down through the tegmentum
and reticular formation of the pons and medulla oblongata ventral to the medial longitudinal bundle. In the medulla the two
bundles are more or less intermingled and the tectospinal portion is continued into the antero-lateral funiculus of the spinal
cord ventral to the rubrospinal fasciculus with which some of its fibers are intermingled. Some of the fibers of the tectospinal fasciculus pass through the red nucleus giving off collaterals to it, others are given off to the motor nuclei of the cranial
nerves and in the spinal cord they terminate either directly or indirectly by terminals and collaterals among the nuclei of the
anterior column. Since the superior colliculus is an important optic reflex center, this tract is probably concerned in optic
reflexes; and possibly also with auditory reflexes since some of the fibers of the central auditory path, the lateral lemniscus,
terminate in the superior colliculus.
The vestibulospinal fasciculus (part of the anterior marginal fasciculus or Loewenthal’s tract) situated chiefly in
the marginal part of the anterior funiculus is mainly derived from the cells of the terminal nuclei of the vestibular nerve,
probably Deiters’s and Bechterew’s, and some of its fibers are supposed to come from the nucleus fastigius (roof nucleus of
the cerebellum). The latter nucleus is intimately connected with Dieters’s and Bechterew’s nuclei. The vestibulospinal fasciculus is concerned with equilibratory reflexes. Its terminals and collaterals end about the motor cells in the anterior column. It extends to the sacral region of the cord. Its fibers are intermingled with the ascending spinothalamic fasciculus,
with the anterior proper fasciculus and laterally with the tectospinal fasciculus. Its fibers are supposed to be both crossed
and uncrossed. In the brain-stem it is associated with the dorsal longitudinal bundle.
The pontospinal fasciculus (Bechterew) arises from the cells in the reticular formation of the pons from the same
and the opposite side and is associated in the brain-stem with the ventral longitudinal bundle. In the cord it is intermingled
with the fibers of the vestibulospinal fasciculus in the anterior funiculus. Not much is known about this tract.
There are probably other descending fasciculi such as the thalamospinal but not much is known about them.
Written tests of central nervous system
I. Questions for self-check
The Nervous System
The _____ nervous system controls voluntary functions.
The _____________ nervous system is composed
of sympathetic and parasympathetic nerves.
The most common type of neuron, structurally, is
the _______________.
All of the nerves outside of the CNS comprise the
_____ nervous system.
_________________ neurons carry signals from the
CNS to the PNS.
_____________ neurotransmitters stop movement
of an impulse.
_____________ is the neurotransmitter that's released into the muscles to activate them.
Neurotransmitters diffuse across the
______________ when passing from neuron to
neuron.
As the diameter of a nerve gets larger, the nerve
impulse moves ____________.
The _____ nervous system controls the involuntary
"fight or flight" response.
A _________________ must be reached before the
action potential is generated.
The resting period after an impulse is created is
called the ______________.
The brain and spinal cord comprise the
___________ nervous system.
Neurons are ___________, which means they can't
reproduce.
The decision-making neurons in the CNS are mainly _____________ neurons.
The Central Nervous System
The thalamus, epithalamus, and hypothalamus are
parts of the ______________.
The midbrain, pons, and medulla are parts of the
_______________.
A _________________ is a cavity in the brain
filled with cerebrospinal fluid.
The _____________ ventricle is a C-shaped chamber. There is one in each cerebral hemisphere.
The _______________ fissure separates the cerebrum into right and left cerebral hemispheres.
The _______________ fissure separates the cerebral hemispheres from the cerebellum below.
The ________________ controls voluntary movement of muscles.
The ________________ in the parietal lobe receives sensory information from the body.
The ________________ in the temporal lobe in
interpretes auditory input (hearing).
The ________________ in the parietal lobe interpretes taste.
The ________________ is the central core of the
brain; it surrounds the 3rd ventricle.
The ____________ regulates body temperature and
food intake.
The ____________ consists of the pineal gland and
the choroid plexus.
The ____________ secretes melatonin, helps regulate the sleep-wake cycle, and relates to mood.
The ____________ is composed of the midbrain,
pons, and medulla.
Heart rate, blood pressure, coughing, and sneezing
are controlled by the ____________.
The ______________ is the emotional center of the
brain. It's located around the diencephalon.
The _______________ are 3 layers of membrane
surrounding the brain and spinal cord.
The outermost layer of the meninges is the
_______________.
Cerebrospinal fluid is formed by the choroid plexus
from _____________.
The ________________ supports and cushions the
brain & spinal cord and helps to nourish them.
___________ can result when blood circulation to
the brain is blocked and tissue dies.
_________ is a degenerative brain disease that
causes slow, progressive loss of memory and motor
control.
There are ______ of spinal nerve roots extending
from the spinal cord.
The outside layer of the spinal cord is
_____________.
The _____________ nerve fibers carry messages
from the brain down the spinal cord.
II. Tests from “Step-1” database (with explanation)
1. A neuroscientist is studying the functioning of
the hypothalamic nuclei by ablating different
parts of a mouse's hypothalamus and then
monitoring the animal's behavior. In one such
experiment, after ablation, the mouse begins to
eat more food and becomes obese over a period
of weeks. Which of the following structures
was likely destroyed in this experiment?
A. Lateral nucleus
B. Septal nucleus
C. Suprachiasmatic nucleus
D. Supraoptic nucleus
E. Ventromedial nucleus
Explanation:
The correct answer is E. The ventromedial nucleus
is thought to be the satiety center of the brain. Bilateral destruction leads to hyperphagia, obesity,
and savage behavior. Stimulation inhibits the urge
to eat.
Destruction of the lateral nucleus (choice A) results
in starvation, whereas stimulation of this nucleus
induces eating.
Destruction of the septal nucleus (choice B) produces aggressive behavior.
The suprachiasmatic nucleus (choice C) receives
direct input from the retina, and plays a role in controlling circadian rhythms.
The supraoptic nucleus (choice D), along with the
periventricular nucleus, regulates water
balance and produces antidiuretic hormone (ADH)
and oxytocin.
2. A patient has a large meningioma involving the
parasagittal region and falx cerebri. Which of
the following neurologic deficits would this
mass lesion be expected to produce?
A. Altered taste
B. Leg paralysis
C. Loss of facial sensation
D. Ptosis
E. Unilateral deafness
Explanation:
The correct answer is B. A meningioma of the parasagittal region and the falx cerebri would be located
superiorly, between the two hemispheres. In this
position, it could compress the sensory (postcentral
gyrus) or motor cortex (precentral gyrus) supplying
the lower extremities.
Taste (choice A) is supplied by cranial nerves VII,
IX, and X. These nerves arise in the brainstem.
Facial sensation (choice C) is supplied by cranial
nerve V, the nuclei of which are in the brainstem.
Ptosis (choice D) can be caused by a deficit in cranial nerve III, which arises from the brainstem.
Unilateral deafness (choice E) suggests damage to
cranial nerve VIII, which arises from the brainstem.
3. What is the most important source of noradrenergic innervation to the cerebral cortex?
A. Basal nucleus of Meynert
B. Caudate nucleus
C. Locus coeruleus
D. Raphe nucleus
E. Substantia nigra
F. Ventral tegmental area
Explanation:
The correct answer is C. The locus coeruleus is a
dense collection of neuromelanin-containing cells
in the rostral pons, near the lateral edge of the floor
of the fourth ventricle. The fact that it appears blueblack in unstained brain tissue gave rise to its name,
which means "blue spot" in Latin. These cells,
which contain norepinephrine, provide the majority
of noradrenergic innervation to the forebrain, including the cerebral cortex.
The basal nucleus of Meynert (choice A), a part of
the substantia innominata, is a major collection of
forebrain cholinergic neurons. These neurons (together with neurons in septal nuclei) innervate the
neocortex, hippocampal formation, and the amyg-
dala. The basal nucleus is one of the structures that
degenerates in Alzheimer's disease.
The caudate nucleus (choice B) is part of the basal
ganglia, located immediately lateral to the lateral
ventricles. There are at least two important cell
types in the caudate. GABAergic projection neurons (the majority) innervate the globus pallidus
and substantia nigra pars reticulata. The GABAergic neurons degenerate in Huntington's disease,
which leads to enlarged lateral ventricles, clearly
visible on MRI. The caudate also contains cholinergic interneurons, which provide most of the acetylcholine to the striatum (caudate and putamen). The
balance of striatal acetylcholine and dopamine is
important for the treatment of patients with extrapyramidal symptoms, such as Parkinson's disease or
parkinsonism accompanying therapy with antipsychotic medications.
The raphe nuclei (choice D) are located in the midline at most levels of the brainstem. They contain
serotonergic cell bodies that innervate virtually every part of the central nervous system.
The substantia nigra (choice E) is located in the
midbrain, and consists of the substantia nigra pars
compacta and the substantia nigra pars reticulata.
The substantia nigra pars compacta contains the
nigrostriatal neurons that are the source of striatal
dopamine. This cell group degenerates in Parkinson's disease or in response to neurotoxic agents
such as MPTP. The substantia nigra pars reticulata
consists predominately of GABAergic neurons that
innervate the thalamus.
The ventral tegmental area (choice F) is located in
the midbrain and is an important source of dopamine for the limbic and cortical areas. These cells
are called mesolimbic and mesocortical neurons.
Overactivity of this cell group is a popular theory of
the etiology of schizophrenia, and is the basis for
the administration of antipsychotic agents (dopamine receptor antagonists).
4. A 54-year-old man is evaluated by a neurologist
because of a gait disorder. When the physician
passively moves the patient's right great toe
upward or downward, the patient cannot accurately report the direction of motion, although
his perception of light touch and painful stimuli
is unimpaired. This finding can best be explained by a lesion of which of the following
structures?
A. Right fasciculus cuneatus
B. Right fasciculus gracilis
C. Right lateral lemniscus
D. Right medial lemniscus
E. Right ventroposterolateral nucleus of the
thalamus
F. Right ventroposteromedial nucleus of the
thalamus
Explanation:
The correct answer is B. The patient's inability to
detect the position of his toe reflects a lack of conscious proprioception for this part of his body. Conscious proprioception, discriminative touch, and
vibration sense are all carried by the dorsal column/medial lemniscus system. The fact that he can
still perceive light touch and painful stimuli indicates that his anterolateral system is unimpaired. In
the dorsal column/medial lemniscus system, the
primary neuron's cell body is located in the dorsal
root ganglia and sends its projection to the cord
through the dorsal roots. The fibers do not synapse
in the cord, but rather ascend the cord in the dorsal
columns. Fibers carrying information from the legs
ascend in the fasciculus gracilis; those receiving
input from the arms project in the fasciculus cuneatus. Both ascend to the caudal medulla, where they
terminate in the nucleus gracilis and nucleus cuneatus, respectively. The secondary neurons originating from these nuclei cross as the internal arcuate
fibers, ascend as the medial lemniscus, then synapse
in the ventroposterolateral (VPL) nucleus of the
thalamus. Tertiary neurons from the VPL project to
the ipsilateral somatosensory cortex. Therefore, a
lack of conscious proprioception from the right toe
could result from lesions to the right fasciculus gracilis, the right nucleus gracilis, the left medial lemniscus, the left VPL, or left somatosensory cortex.
The right fasciculus cuneatus (choice A) carries
discriminative touch, proprioception, and vibration
information from the upper extremities.
The right lateral lemniscus (choice C), part of the
auditory system, receives input from the contralateral cochlear nuclei and from the superior olivary
nuclei, and projects to the inferior colliculus.
The right medial lemniscus (choice D) carries discriminative touch, proprioception, and vibration
information from the left side of the body.
The right ventroposterolateral (VPL) nucleus of the
thalamus (choice E) receives all sensory information (including pain and temperature information) from the left side of the body.
The right ventroposteromedial (VPM) nucleus of
the thalamus (choice F) receives all sensory information from the left side of the face.
III. Tests from “Krok-1” database
1. After a stroke (cerebral hemorrhage) a patient
does not have voluntary movements of muscles
of head and neck. Brain examination with the
help of NMR detected that haematoma is in the
knee of the internal capsule. Which conduction
tract has been damaged?
A. *Corticonuclear.
B. Corticospinal.
C. Corticothalamic.
D. Frontopontine.
E. Thalamocortical.
2. A patient after a brain blood supply disturbance
lost the ability to write letters and figures. In
what lobe of the brain was the pathology?
A. Occipital.
B. *Frontal.
C. Temporal.
D. Parietal.
E. Insula.
3. A 63-year-old patient applied to a neuropathologist complaining of inability to perform
woodwork which demands accuracy, as his
right hand had been doing a lot of errant
movements for 3 months. Examination showed
that the patient had injured:
A. Angular gyrus.
B. Precentral gyrus.
C. Postcentral gyrus.
D. Superior temporal gyrus.
E. *Supramarginal gyrus.
4. A 45-year-old patient had a severe brain blood
circulation disturbance. After stabilization of
the general condition he is unable to pronounce
words distinctly. Damage of what area of cerebral cortex caused the impairment of the
speech-motor center?
A. Angular gyrus.
B. *Inferior frontal gyrus.
C. Supramarginal gyrus.
D. Precentral gyrus.
E. Superior temporal gyrus.
5. After a cerebral hemorrhage (hemorrhagic
stroke) a patient could pronounce words with a
big effort (motor aphasia). Which convolution
of brain was injured?
A. Superior frontal.
B. *Inferior frontal.
C. Superior temporal.
D. Inferior temporal.
E. –
6. The growth of a tumor in the cavity of the third
ventricle of brain caused such vegetative disorders as sleep disturbance, disorder of thermoregulation, all kinds of metabolism, diabetes
insipidus. The irritation of nuclei of what part
of the brain caused these symptoms?
A. Medulla oblongata.
B. Cerebral peduncles.
C. Mesencephalic tegmentum.
D. Pons.
E. *Hypothalamus.
7. X-ray examination of a skull has shown ephippium enlargement caused by a brain tumor.
What part of the brain has pathological changes?
A. Metathalamus.
B. Thalamus.
C. *Hypothalamus.
D. Epithalamus.
E. Tectum of mesencephalon.
8. As a result of a traffic accident a victim sustained an injury of the spinal column. Examination has shown the right-side paralysis of the
lower extremity with muscles tone increase.
Which part of the central nervous system was
injured?
A. *Right corticospinal tract.
B. Anterior horn of spinal cord.
C. Posterior horn of spinal cord.
D. Anterior funiculus of spinal cord.
E. Medulla oblongata.
9. After a craniocerebral trauma a 47-year-old
man appealed with complaints of impossibility
of exact movements of the upper extremities: he
can not button, light a match, pour water into a
glass. Examination has shown that muscle
strength, deep muscular sense, and mechanisms
of coordination are preserved. Which site of
cerebral cortex has been affected?
A. *Supramarginal gyrus.
B. Calcarine sulcus.
C. Precentral gyrus.
D. Temporal gyri.
E. Angular gyrus.
10. During work a patient gets tired quickly. In upright position with closed eyes he staggers, loses balance. The tonus of skeletal muscle is reduced. Which structure of brain is injured most
probably?
A. Cerebellum.
B. Limbic system.
C. Basal ganglions.
D. Precentral gyrus of cortex.
E. Thalamus.
11. A 35-year-old man has a sharp hearing injury
after meningoencephalitis. Examination excludes sound-conducting and sound-perceiving
apparatus pathology. Which gyrus of brain is
damaged?
A. Angular.
B. Middle temporal.
C. Superior frontal.
D. Supramarginal.
E. *Superior temporal.
12. A hemorrhage in the occipital lobe (calcarinum
sulcus zone) has appeared. Which functions of
organism are violated?
A. Movements are absent.
B. Hearing is absent.
C. Olfaction is absent.
D. *Vision is absent.
E. Sensitivity is absent.
13. A 41-year-old patient was admitted to an infectious department with fever. Objectively there
are meningeal symptoms. Which anatomical
formation must a needle penerate taking a spinal puncture?
A. *Spatium subarachnoideum.
B. Spatium subdurale.
14.
15.
16.
17.
18.
19.
C. Spatium epidurale.
D. Cavum trigeminale.
E. Cisterna cerebellomedullaris.
After a long-term chronic disease of the brain a
patient has involuntary movements, violated
muscular tonus. Which conduction tract disorder do these symptoms indicate?
A. Tractus tectospinalis.
B. Tractus corticospinalis.
C. Tractus corticonuclearis.
D. Tractus spinothalamicus lateralis.
E. *Tractus rubrospinalis.
After a craniocerebral trauma skin sensitivity is
reduced. Which part of the cerebral cortex
might be damaged?
A. *Postcentral gyrus.
B. Occipital part.
C. Cingulate gyrus.
D. Frontal part of cortex.
E. Precentral gyrus.
Occlusive syndrome develops in case of liquor
tracts blockade on the level of the middle and
lateral ventricle apertures. Into which space is
liquor outflow complicated?
A. Third ventricle.
B. Lateral ventricles.
C. Aqueduct of cerebrum.
D. *Subarachnoid space.
E. Fourth ventricle.
During investigation of patient, it was found
formation in the white substance of cerebral
hemispheres with location in the knee and
frontal part of posterior crus of internal capsule.
Fibres of what conductive tract of the brain will
be disrupted?
A. Tr. frontopontinus
B. *Tr. pyramidalis
C. Tr. frontothalamicus
D. Tr. parietooccipitopontinus
E. Тr. thalamocorticalis
Vegetative abnormalities in the sleep, heat
regulation, all kinds of metabolism, diabetes insipidus are developing in the patient due to
grouth of the tumour in the III ventricle of
brain. Irritation of the nucleus of what part of
the brain can cause this symptoms?
A. Medulla
B. Cerebral peduncles (cruces cerebri)
C. Pons cerebelli
D. Mesencephalic tegmentum
E. Hypothalamus
In the experiment on the animal the part of the
cerebral cortex hemispheres was removed. It
caused elimination of previously formed conditioned reflex to the light irritation. What part of
the cortex was removed?
A. *Occipital cortex
B. Precentral convolution
C. Limbic cortex
20.
21.
22.
23.
24.
D. Temporal lobe
E. Postcentral convolution
A 60-year-old man after cerebral hemorrhage
felt asleep for a long time. Damage of what
structure caused this state?
A. Nuclei of the cranial nerves
B. Hippocampus
C. *Reticular formation
D. Cortex of the large hemispheres
E. Black substances
Due to cranial trauma the patient developed the
symptoms: intention tremor, dysmetry, adiadochokinesis, dysarthria. What structure of the
brain is injured?
A. *Cerebellum
B. Motor cortex
C. Striatum
D. Black substance
E. Pale sphere
A patient becomes quickly tired during his
work. In vertical position with closed eyes he is
dizzying and loosing equilibrium. Skeletal
muscle tone is reduced. Which of the belowmentioned brain structures is damaged?
A. *Cerebellum
B. Hypothalamus
C. Precentral gyrus of cerebral hemispheres
cortex
D. Basal ganglia
E. Thalamus
A patient with brain bloodstream disorder has
got difficulties with swallowing, he can choke
over while eating liquid food. What part of the
brain is damaged?
A. *Medulla
B. Midbrain
C. Cerebellum
D. Thalamencephalon
E. Cervical part of the spinal medulla
After brain injuiry a patient has lost his vision.
What zone of the brain cortex is damaged in
this case?
A. Temporal and parietal
B. Temporal
C. *Occipital
25.
26.
27.
28.
D. Frontal
E. Parietal
When a patient with traumatic impairment of
the brain was examined, it was discovered that
he had stopped to distinguish displacement of
an object on the skin. What part of the brain
was damaged?
A. Parietal zone of the cortex
B. *Posterior central gurus
C. Occipital zone of the cortex
D. Frontal central gurus
E. Frontal zone
A 50-year-old patient was injured on the occipital region of the head. The closed skull trauma
was diagnosed. She was taken to the hospital.
The medical examination: deregulation of walking and balance, trembling of arms. What part
of brain was injured?
A. The medulla oblongata
B. The inter-brain
C. The spinal cord
D. *The cerebellum
E. The mid-brain
During examination of a patient, there was
found a neoplasm in the white substance of cerebral hemispheres with localization in the knee
and frontal part of posterior crus of internal
capsule. Fibres of what conductive tract of the
brain will be disrupted?
A. Tr. parietooccipitopontinus
B. Тr. thalamocorticalis
C. Tr. frontopontinus
D. Tr. frontothalamicus
E. *Tr. pyramidalis
When a patient with traumatic impairment of
the brain was examined, it was discovered that
he had stopped to distinguish displacement of
an object on the skin. What part of the brain
was damaged?
A. Occipital zone of the cortex
B. *Posterior central gurus
C. Parietal zone of the cortex
D. Frontal central gurus
E. Frontal zone
UNIT 12. SENSORY ORGANS
Practice class 5. Written tests and examination of practice skills of CNS. Examination of
self-taught tasks. Review of sensory organs. The organs of smell and taste.
The aim: to learn the anatomic and functional significance of sensory organs; to learn structure and topography of the organs of smell and taste; to learn the conducting tracts of smell and taste.
Professional orientation: the knowledge of this topic is necessary for doctors of all specialities; it represents special interest for therapists.
The plan of the practice class:
A. Checking of the home assignment: oral quiz or written test control – 30 minutes.
B. Summary lecture on the topic by teacher – 30 minutes.
a) The external nose.
b) The nasal cavity.
c) The structure of the mucous membrane of the nasal cavity.
d) Vessels and nerves of the organ of smell.
e) The accessory sinuses of the nose.
f) The organ of taste.
C. Students’ self-taught time – 55 minutes
D. Home-task – 5 minutes
The organs of the senses may be divided into (a) those of the special senses of taste, smell, sight, and hearing, and
(b) those associated with the general sensations of heat, cold, pain, pressure, etc.
The Organ of Smell
(Organon Olfactorius; The Nose)
The peripheral olfactory organ or organ of smell consists of two parts: an outer, the external nose, which projects
from the center of the face; and an internal, the nasal cavity, which is divided by a septum into right and left nasal chambers.
The External Nose (Nasus Externus; Outer Nose)—The external nose is pyramidal in form, and its upper angle
or root is connected directly with the forehead; its free angle is termed the apex. Its base is perforated by two elliptical
orifices, the nares, separated from each other by an antero-posterior septum, the columna. The margins of the nares are
provided with a number of stiff hairs, or vibrissae, which arrest the passage of foreign substances carried with the current
of air intended for respiration. The lateral surfaces of the nose form, by their union in the middle line, the dorsum nasi, the
direction of which varies considerably in different individuals; the upper part of the dorsum is supported by the nasal bones,
and is named the bridge. The lateral surface ends below in a rounded eminence, the ala nasi.
Structure.—The frame-work of the external nose is composed of bones and cartilages; it is covered by the integument, and lined by mucous membrane.
The bony frame-work occupies the upper part of the organ; it consists of the nasal bones, and the frontal processes
of the maxillae.
The cartilaginous frame-work (cartilagines nasi) consists of five large pieces, viz., the cartilage of the septum,
the two lateral and the two greater alar cartilages, and several smaller pieces, the lesser alar cartilages. The various
cartilages are connected to each other and to the bones by a tough fibrous membrane.
The cartilage of the septum (cartilago septi nasi) is somewhat quadrilateral in form, thicker at its margins than at
its center, and completes the separation between the nasal cavities in front. Its anterior margin, thickest above, is connected
with the nasal bones, and is continuous with the anterior margins of the lateral cartilages; below, it is connected to the medial crura of the greater alar cartilages by fibrous tissue. Its posterior margin is connected with the perpendicular plate of
the ethmoid; its inferior margin with the vomer and the palatine processes of the maxillae.
It may be prolonged backward (especially in children) as a narrow process, the sphenoidal process, for some distance between the vomer and perpendicular plate of the ethmoid. The septal cartilage does not reach as far as the lowest
part of the nasal septum. This is formed by the medial crura of the greater alar cartilages and by the skin; it is freely movable, and hence is termed the septum mobile nasi.
The lateral cartilage (cartilago nasi lateralis; upper lateral cartilage) is situated below the inferior margin of the
nasal bone, and is flattened, and triangular in shape. Its anterior margin is thicker than the posterior, and is continuous
above with the cartilage of the septum, but separated from it below by a narrow fissure; its superior margin is attached to
the nasal bone and the frontal process of the maxilla; its inferior margin is connected by fibrous tissue with the greater alar
cartilage.
The greater alar cartilage (cartilago alaris major; lower lateral cartilage) is a thin, flexible plate, situated immediately below the preceding, and bent upon itself in such a manner as to form the medial and lateral walls of the naris of its
own side. The portion which forms the medial wall (crus mediale) is loosely connected with the corresponding portion of
the opposite cartilage, the two forming, together with the thickened integument and subjacent tissue, the septum mobile
nasi. The part which forms the lateral wall (crus laterale) is curved to correspond with the ala of the nose; it is oval and
flattened, narrow behind, where it is connected with the frontal process of the maxilla by a tough fibrous membrane, in
which are found three or four small cartilaginous plates, the lesser alar cartilages (cartilagines alares minores; sesamoid
cartilages). Above, it is connected by fibrous tissue to the lateral cartilage and front part of the cartilage of the septum; be-
low, it falls short of the margin of the naris, the ala being completed by fatty and fibrous tissue covered by skin. In front,
the greater alar cartilages are separated by a notch which corresponds with the apex of the nose.
The muscles acting on the external nose have been described in the section on Myology.
The integument of the dorsum and sides of the nose is thin, and loosely connected with the subjacent parts; but over
the tip and alae it is thicker and more firmly adherent, and is furnished with a large number of sebaceous follicles, the orifices of which are usually very distinct.
The arteries of the external nose are the alar and septal branches of the external maxillary, which supply the alae
and septum; the dorsum and sides being supplied from the dorsal nasal branch of the ophthalmic and the infraorbital branch
of the internal maxillary. The veins end in the anterior facial and ophthalmic veins.
The nerves for the muscles of the nose are derived from the facial, while the skin receives branches from the infratrochlear and nasociliary branches of the ophthalmic, and from the infraorbital of the maxillary.
The Nasal Cavity (Cavum Nasi; Nasal Fossa)—The nasal chambers are situated one on either side of the median
plane. They open in front through the nares, and communicate behind through the choanae with the nasal part of the pharynx. The nares are somewhat pear-shaped apertures, each measuring about 2.5 cm. antero-posteriorly and 1.25 cm. transversely at its widest part. The choanae are two oval openings each measuring 2.5 cm. in the vertical, and 1.25 cm. in the
transverse direction in a well-developed adult skull.
Inside the aperture of the nostril is a slight dilatation, the vestibule, bounded laterally by the ala and lateral crus of
the greater alar cartilage, and medially by the medial crus of the same cartilage. It is lined by skin containing hairs and sebaceous glands, and extends as a small recess toward the apex of the nose. Each nasal cavity, above and behind the vestibule, is divided into two parts: an olfactory region, consisting of the superior nasal concha and the opposed part of the septum, and a respiratory region, which comprises the rest of the cavity.
Lateral Wall.—On the lateral wall are the superior, middle, and inferior nasal conchae, and below and lateral to
each concha is the corresponding nasal passage or meatus. Above the superior concha is a narrow recess, the sphenoethmoidal recess, into which the sphenoidal sinus opens. The superior meatus is a short oblique passage extending about
half-way along the upper border of the middle concha; the posterior ethmoidal cells open into the front part of this meatus.
The middle meatus is below and lateral to the middle concha, and is continued anteriorly into a shallow depression, situated above the vestibule and named the atrium of the middle meatus. On raising or removing the middle concha the lateral
wall of this meatus is fully displayed. On it is a rounded elevation, the bulla ethmoidalis, and below and in front of this is a
curved cleft, the hiatus semilunaris.
The bulla ethmoidalis is caused by the bulging of the middle ethmoidal cells which open on or immediately above
it, and the size of the bulla varies with that of its contained cells.
The hiatus semilunaris is bounded inferiorly by the sharp concave margin of the uncinate process of the ethmoid
bone, and leads into a curved channel, the infundibulum, bounded above by the bulla ethmoidalis and below by the lateral
surface of the uncinate process of the ethmoid. The anterior ethmoidal cells open into the front part of the infundibulum,
and this in slightly over 50 per cent. of subjects is directly continuous with the frontonasal duct or passage leading from the
frontal air sinus; but when the anterior end of the uncinate process fuses with the front part of the bulla, this continuity is
interrupted and the frontonasal duct then opens directly into the anterior end of the middle meatus.
Below the bulla ethmoidalis, and partly hidden by the inferior end of the uncinate process, is the ostium maxillare,
or opening from the maxillary sinus; in a frontal section this opening is seen to be placed near the roof of the sinus. An accessory opening from the sinus is frequently present below the posterior end of the middle nasal concha. The inferior meatus is below and lateral to the inferior nasal concha; the nasolacrimal duct opens into this meatus under cover of the anterior part of the inferior concha.
Medial Wall.—The medial wall or septum is frequently more or less deflected from the median plane, thus lessening the size of one nasal cavity and increasing that of the other; ridges or spurs of bone growing into one or other cavity
from the septum are also sometimes present. Immediately over the incisive canal at the lower edge of the cartilage of the
septum a depression, the nasopalatine recess, is seen. In the septum close to this recess a minute orifice may be discerned;
it leads backward into a blind pouch, the rudimentary vomeronasal organ of Jacobson, which is supported by a strip of
cartilage, the vomeronasal cartilage. This organ is well-developed in many of the lower animals, where it apparently plays
a part in the sense of smell, since it is supplied by twigs of the olfactory nerve and lined by epithelium similar to that in the
olfactory region of the nose.
The roof of the nasal cavity is narrow from side to side, except at its posterior part, and may be divided, from behind
forward, into sphenoidal, ethmoidal, and frontonasal parts, after the bones which form it.
The floor is concave from side to side and almost horizontal antero-posteriorly; its anterior three-fourths are formed
by the palatine process of the maxilla, its posterior fourth by the horizontal process of the palatine bone. In its anteromedial
part, directly over the incisive foramen, a small depression, the nasopalatine recess, is sometimes seen; it points downward
and forward and occupies the position of a canal which connected the nasal with the buccal cavity in early fetal life.
The Mucous Membrane (membrana mucosa nasi).—The nasal mucous membrane lines the nasal cavities, and is
intimately adherent to the periosteum or perichondrium. It is continuous with the skin through the nares, and with the mucous membrane of the nasal part of the pharynx through the choanae. From the nasal cavity its continuity with the conjunctiva may be traced, through the nasolacrimal and lacrimal ducts; and with the frontal, ethmoidal, sphenoidal, and maxillary
sinuses, through the several openings in the meatuses. The mucous membrane is thickest, and most vascular, over the nasal
conchae. It is also thick over the septum; but it is very thin in the meatuses on the floor of the nasal cavities, and in the various sinuses.
Owing to the thickness of the greater part of this membrane, the nasal cavities are much narrower, and the middle
and inferior nasal conchae appear larger and more prominent than in the skeleton; also the various apertures communicating with the meatuses are considerably narrowed.
Structure of the Mucous Membrane.—The epithelium covering the mucous membrane differs in its character according to the functions of the part of the nose in which it is found. In the respiratory region it is columnar and ciliated.
Interspersed among the columnar cells are goblet or mucin cells, while between their bases are found smaller pyramidal
cells. Beneath the epithelium and its basement membrane is a fibrous layer infiltrated with lymph corpuscles, so as to form
in many parts a diffuse adenoid tissue, and under this a nearly continuous layer of small and larger glands, some mucous
and some serous, the ducts of which open upon the surface. In the olfactory region the mucous membrane is yellowish in
color and the epithelial cells are columnar and non-ciliated; they are of two kinds, supporting cells and olfactory cells. The
supporting cells contain oval nuclei, which are situated in the deeper parts of the cells and constitute the zone of oval nuclei; the superficial part of each cell is columnar, and contains granules of yellow pigment, while its deep part is prolonged
as a delicate process which ramifies and communicates with similar processes from neighboring cells, so as to form a network in the mucous membrane. Lying between the deep processes of the supporting cells are a number of bipolar nerve
cells, the olfactory cells, each consisting of a small amount of granular protoplasm with a large spherical nucleus, and possessing two processes—a superficial one which runs between the columnar epithelial cells, and projects on the surface of
the mucous membrane as a fine, hair-like process, the olfactory hair; the other or deep process runs inward, is frequently
beaded, and is continued as the axon of an olfactory nerve fiber. Beneath the epithelium, and extending through the thickness of the mucous membrane, is a layer of tubular, often branched, glands, the glands of Bowman, identical in structure
with serous glands. The epithelial cells of the nose, fauces and respiratory passages play an important role in the maintenance of an equable temperature, by the moisture with which they keep the surface always slightly lubricated.
Vessels and Nerves.—The arteries of the nasal cavities are the anterior and posterior ethmoidal branches of the
ophthalmic, which supply the ethmoidal cells, frontal sinuses, and roof of the nose; the sphenopalatine branch of the which
supplies the mucous membrane covering the conchae, the meatuses and septum, the septal branch of the superior labial of
the external maxillary; the infraorbital and alveolar branches of the internal maxillary, which supply the lining membrane
of the maxillary sinus; and the pharyngeal branch of the same artery, distributed to the sphenoidal sinus. The ramifications
of these vessels form a close plexiform net-work, beneath and in the substance of the mucous membrane.
The veins form a close cavernous plexus beneath the mucous membrane. This plexus is especially well-marked over
the lower part of the septum and over the middle and inferior conchae. Some of the veins open into the sphenopalatine vein;
others join the anterior facial vein; some accompany the ethmoidal arteries, and end in the ophthalmic veins; and, lastly, a
few communicate with the veins on the orbital surface of the frontal lobe of the brain, through the foramina in the cribriform plate of the ethmoid bone; when the foramen cecum is patent it transmits a vein to the superior sagittal sinus.
The nerves of ordinary sensation are: the nasociliary branch of the ophthalmic, filaments from the anterior alveolar
branch of the maxillary, the nerve of the pterygoid canal, the nasopalatine, the anterior palatine, and nasal branches of the
sphenopalatine ganglion.
The nasociliary branch of the ophthalmic distributes filaments to the forepart of the septum and lateral wall of the
nasal cavity. Filaments from the anterior alveolar nerve supply the inferior meatus and inferior concha. The nerve of the
pterygoid canal supplies the upper and back part of the septum, and superior concha; and the upper nasal branches from the
sphenopalatine ganglion have a similar distribution. The nasopalatine nerve supplies the middle of the septum. The anterior
palatine nerve supplies the lower nasal branches to the middle and inferior conchae.
The olfactory, the special nerve of the sense of smell, is distributed to the olfactory region. Its fibers arise from the
bipolar olfactory cells and are destitute of medullary sheaths. They unite in fasciculi which form a plexus beneath the mucous membrane and then ascend in grooves or canals in the ethmoid bone; they pass into the skull through the foramina in
the cribriform plate of the ethmoid and enter the under surface of the olfactory bulb, in which they ramify and form synapses with the dendrites of the mitral cells.
The Accessory Sinuses of the Nose (Sinus Paranasales).
The accessory sinuses or air cells of the nose are the frontal, ethmoidal, sphenoidal, and maxillary; they vary in
size and form in different individuals, and are lined by ciliated mucous membrane directly continuous with that of the nasal
cavities.
The Frontal Sinuses (sinus frontales), situated behind the superciliary arches, are rarely symmetrical, and the septum between them frequently deviates to one or other side of the middle line. Their average measurements are as follows:
height, 3 cm.; breadth, 2.5 cm.; depth from before backward, 2.5 cm. Each opens into the anterior part of the corresponding
middle meatus of the nose through the frontonasal duct which traverses the anterior part of the labyrinth of the ethmoid.
Absent at birth, they are generally fairly well developed between the seventh and eighth years, but only reach their full size
after puberty.
The Ethmoidal Air Cells (cellulae ethmoidales) consist of numerous thin-walled cavities situated in the ethmoidal
labyrinth and completed by the frontal, maxilla, lacrimal, sphenoidal, and palatine. They lie between the upper parts of the
nasal cavities and the orbits, and are separated from these cavities by thin bony laminae. On either side they are arranged in
three groups, anterior, middle, and posterior. The anterior and middle groups open into the middle meatus of the nose, the
former by way of the infundibulum, the latter on or above the bulla ethmoidalis. The posterior cells open into the superior
meatus under cover of the superior nasal concha; sometimes one or more opens into the sphenoidal sinus. The ethmoidal
cells begin to develop during fetal life.
The Sphenoidal Sinuses (sinus sphenoidales) contained within the body of the sphenoid vary in size and shape; owing to the lateral displacement of the intervening septum they are rarely symmetrical. The following are their average
measurements: vertical height, 2.2 cm.; transverse breadth, 2 cm.; antero-posterior depth, 2.2 cm. When exceptionally large
they may extend into the roots of the pterygoid processes or great wings, and may invade the basilar part of the occipital
bone. Each sinus communicates with the sphenoethmoidal recess by means of an aperture in the upper part of its anterior
wall. They are present as minute cavities at birth, but their main development takes place after puberty.
The Maxillary Sinus (sinus maxillaris; antrum of Highmore), the largest of the accessory sinuses of the nose, is a
pyramidal cavity in the body of the maxilla. Its base is formed by the lateral wall of the nasal cavity, and its apex extends
into the zygomatic process. Its roof or orbital wall is frequently ridged by the infra-orbital canal, while its floor is formed
by the alveolar process and is usually 1/2 to 10 mm. below the level of the floor of the nose; projecting into the floor are
several conical elevations corresponding with the roots of the first and second molar teeth, and in some cases the floor is
perforated by one or more of these roots. The size of the sinus varies in different skulls, and even on the two sides of the
same skull. The adult capacity varies from 9.5 c.c. to 20 c.c., average about 14.75 c.c. The following measurements are
those of an average-sized sinus: vertical height opposite the first molar tooth, 3.75 cm.; transverse breadth, 2.5 cm.; anteroposterior depth, 3 cm. In the antero-superior part of its base is an opening through which it communicates with the lower
part of the hiatus semilunaris; a second orifice is frequently seen in, or immediately behind, the hiatus. The maxillary sinus
appears as a shallow groove on the medial surface of the bone about the fourth month of fetal life, but does not reach its full
size until after the second dentition. At birth it measures about 7 mm. in the dorso-ventral direction and at twenty months
about 20 mm.
The Organs of Taste (Organon Gustus)
The peripheral gustatory or taste organs consist of certain modified epithelial cells arranged in flask-shaped
groups termed gustatory calyculi (taste-buds), which are found on the tongue and adjacent parts. They occupy nests in the
stratified epithelium, and are present in large numbers on the sides of the papillae vallatae, and to a less extent on their opposed walls. They are also found on the fungiform papillae over the back part and sides of the tongue, and in the general
epithelial covering of the same areas. They are very plentiful over the fimbriae linguae, and are also present on the under
surface of the soft palate, and on the posterior surface of the epiglottis.
Structure.—Each taste bud is flask-like in shape, its broad base resting on the corium, and its neck opening by an
orifice, the gustatory pore, between the cells of the epithelium. The bud is formed by two kinds of cells: supporting cells
and gustatory cells. The supporting cells are mostly arranged like the staves of a cask, and form an outer envelope for the
bud. Some, however, are found in the interior of the bud between the gustatory cells. The gustatory cells occupy the central portion of the bud; they are spindle-shaped, and each possesses a large spherical nucleus near the middle of the cell.
The peripheral end of the cell terminates at the gustatory pore in a fine hair-like filament, the gustatory hair. The central
process passes toward the deep extremity of the bud, and there ends in single or bifurcated varicosities. The nerve fibrils
after losing their medullary sheaths enter the taste bud, and end in fine extremities between the gustatory cells; other nerve
fibrils ramify between the supporting cells and terminate in fine extremities; these, however, are believed to be nerves of
ordinary sensation and not gustatory.
Nerves of Taste.—The chorda tympani nerve, derived from the sensory root of the facial, is the nerve of taste for the
anterior two-thirds of the tongue; the nerve for the posterior third is the glossopharyngeal.
Practice skills
Students are supposed to identify the following structures on the samples:
Practice class 6. The structure of organ of vision. The pupil reflex. The conducting tract of visual
analyzer.
The aim: to learn the structure of the organ of vision; to learn the conducting tract of vision.
Professional orientation: the knowledge of this topic is necessary for doctors of all specialities; it represents special interest for ophthalmologists, neuropathologists and others.
The plan of the practice class:
A. Checking of the home assignment: oral quiz or written test control – 30 minutes.
B. Summary lecture on the topic by teacher – 30 minutes.
a) The general structure of the organ of sight.
b) The development of the eyeball.
c) The refracting media.
d) Vessels and nerves of the eyeball.
C. Students’ self-taught time – 55 minutes
D. Home-task – 5 minutes
The Organ of Sight (Organon Visus; The Eye)
The bulb of the eye (bulbus oculi; eyeball), or organ of sight, is contained in the cavity of the orbit, where it is protected from injury and moved by the ocular muscles. Associated with it are certain accessory structures, viz., the muscles,
fasciae, eyebrows, eyelids, conjunctiva, and lacrimal apparatus.
The bulb of the eye is imbedded in the fat of the orbit, but is separated from it by a thin membranous sac, the fascia
bulbi. It is composed of segments of two spheres of different sizes. The anterior segment is one of a small sphere; it is
transparent, and forms about one-sixth of the bulb. It is more prominent than the posterior segment, which is one of a larger
sphere, and is opaque, and forms about five-sixths of the bulb. The term anterior pole is applied to the central point of the
anterior curvature of the bulb, and that of posterior pole to the central point of its posterior curvature; a line joining the two
poles forms the optic axis. The axes of the two bulbs are nearly parallel, and therefore do not correspond to the axes of the
orbits, which are directed forward and lateralward. The optic nerves follow the direction of the axes of the orbits, and are
therefore not parallel; each enters its eyeball 3 mm. to the nasal side and a little below the level of the posterior pole. The
bulb measures rather more in its transverse and antero-posterior diameters than in its vertical diameter, the former amounting to about 24 mm., the latter to about 23.5 mm.; in the female all three diameters are rather less than in the male; its antero-posterior diameter at birth is about 17.5 mm., and at puberty from 20 to 21 mm.
Development.—The eyes begin to develop as a pair of diverticula from the lateral aspects of the forebrain. These
diverticula make their appearance before the closure of the anterior end of the neural tube; after the closure of the tube they
are known as the optic vesicles. They project toward the sides of the head, and the peripheral part of each expands to form
a hollow bulb, while the proximal part remains narrow and constitutes the optic stalk. The ectoderm overlying the bulb
becomes thickened, invaginated, and finally severed from the ectodermal covering of the head as a vesicle of cells, the lens
vesicle, which constitutes the rudiment of the crystalline lens. The outer wall of the bulb becomes thickened and invaginated, and the bulb is thus converted into a cup, the optic cup, consisting of two strata of cells. These two strata are continuous with each other at the cup margin, which ultimately overlaps the front of the lens and reaches as far forward as the future aperture of the pupil. The invagination is not limited to the outer wall of the bulb, but involves also its postero-inferior
surface and extends in the form of a groove for some distance along the optic stalk, so that, for a time, a gap or fissure, the
choroidal fissure, exists in the lower part of the cup. Through the groove and fissure the mesoderm extends into the optic
stalk and cup, and in this mesoderm a bloodvessel is developed; during the seventh week the groove and fissure are closed
and the vessel forms the central artery of the retina. Sometimes the choroidal fissure persists, and when this occurs the choroid and iris in the region of the fissure remain undeveloped, giving rise to the condition known as coloboma of the choroid
or iris.
The retina is developed from the optic cup. The outer stratum of the cup persists as a single layer of cells which assume a columnar shape, acquire pigment, and form the pigmented layer of the retina; the pigment first appears in the cells
near the edge of the cup. The cells of the inner stratum proliferate and form a layer of considerable thickness from which
the nervous elements and the sustentacular fibers of the retina, together with a portion of the vitreous body, are developed.
In that portion of the cup which overlaps the lens the inner stratum is not differentiated into nervous elements, but forms a
layer of columnar cells which is applied to the pigmented layer, and these two strata form the pars ciliaris and pars iridica
retinae.
The cells of the inner or retinal layer of the optic cup become differentiated into spongioblasts and germinal cells,
and the latter by their subdivisions give rise to neuroblasts. From the spongioblasts the sustentacular fibers of Müller, the
outer and inner limiting membranes, together with the groundwork of the molecular layers of the retina are formed. The
neuroblasts become arranged to form the ganglionic and nuclear layers. The layer of rods and cones is first developed in the
central part of the optic cup, and from there gradually extends toward the cup margin. All the layers of the retina are completed by the eighth month of fetal life.
The optic stalk is converted into the optic nerve by the obliteration of its cavity and the growth of nerve fibers into
it. Most of these fibers are centripetal, and grow backward into the optic stalk from the nerve cells of the retina, but a few
extend in the opposite direction and are derived from nerve cells in the brain. The fibers of the optic nerve receive their
medullary sheaths about the tenth week after birth. The optic chiasma is formed by the meeting and partial decussation of
the fibers of the two optic nerves. Behind the chiasma the fibers grow backward as the optic tracts to the thalami and midbrain.
The crystalline lens is developed from the lens vesicle, which recedes within the margin of the cup, and becomes
separated from the overlying ectoderm by mesoderm. The cells forming the posterior wall of the vesicle lengthen and are
converted into the lens fibers, which grow forward and fill up the cavity of the vesicle. The cells forming the anterior wall
retain their cellular character, and form the epithelium on the anterior surface of the adult lens. By the second month the
lens is invested by a vascular mesodermal capsule, the capsula vasculosa lentis; the bloodvessels supplying the posterior
part of this capsule are derived from the hyaloid artery; those for the anterior part from the anterior ciliary arteries; the portion of the capsule which covers the front of the lens is named the pupillary membrane. By the sixth month all the vessels
of the capsule are atrophied except the hyaloid artery, which disappears during the ninth month; the position of this artery is
indicated in the adult by the hyaloid canal, which reaches from the optic disk to the posterior surface of the lens. With the
loss of its bloodvessels the capsula vasculosa lentis disappears, but sometimes the pupillary membrane persists at birth,
giving rise to the condition termed congenital atresia of the pupil.
The vitreous body is developed between the lens and the optic cup. The lens rudiment and the optic vesicle are at
first in contact with each other, but after the closure of the lens vesicle and the formation of the optic cup the former withdraws itself from the retinal layer of the cup; the two, however, remain connected by a network of delicate protoplasmic
processes. This network, derived partly from the cells of the lens and partly from those of the retinal layer of the cup, constitutes the primitive vitreous body. At first these protoplasmic processes spring from the whole of the retinal layer of the
cup, but later are limited to the ciliary region, where by a process of condensation they appear to form the zonula ciliaris.
The mesoderm which enters the cup through the choroidal fissure and around the equator of the lens becomes intimately
united with this reticular tissue, and contributes to form the vitreous body, which is therefore derived partly from the ectoderm and partly from the mesoderm.
The anterior chamber of the eye appears as a cleft in the mesoderm separating the lens from the overlying ectoderm. The layer of mesoderm in front of the cleft forms the substantia propria of the cornea, that behind the cleft the stroma
of the iris and the pupillary membrane. The fibers of the ciliary muscle are derived from the mesoderm, but those of the
Sphincter and Dilatator pupillae are of ectodermal origin, being developed from the cells of the pupillary part of the optic
cup.
The sclera and choroid are derived from the mesoderm surrounding the optic cup.
The eyelids are formed as small cutaneous folds, which about the middle of the third month come together and unite
in front of the cornea. They remain united until about the end of the sixth month.
The lacrimal sac and nasolacrimal duct result from a thickening of the ectoderm in the groove, nasoöptic furrow,
between the lateral nasal and maxillary processes. This thickening forms a solid cord of cells which sinks into the mesoderm; during the third month the central cells of the cord break down, and a lumen, the nasolacrimal duct, is established.
The lacrimal ducts arise as buds from the upper part of the cord of cells and secondarily establish openings (puncta lacrimalia) on the margins of the lids. The epithelium of the cornea and conjunctiva, and that which lines the ducts and alveoli
of the lacrimal gland, are of ectodermal origin, as are also the eyelashes and the lining cells of the glands which open on
the lid-margins.
The Refracting Media
The refracting media are three, viz.: (a) aqueous humor, (b) vitreous body (с) crystalline lens.
The Aqueous Humor (humor aqueus).—The aqueous humor fills the anterior and posterior chambers of the eyeball. It is small in quantity, has an alkaline reaction, and consists mainly of water, less than one-fiftieth of its weight being
solid matter, chiefly chloride of sodium.
The Vitreous Body (corpus vitreum).—The vitreous body forms about four-fifths of the bulb of the eye. It fills the
concavity of the retina, and is hollowed in front, forming a deep concavity, the hyaloid fossa, for the reception of the lens.
It is transparent, of the consistence of thin jelly, and is composed of an albuminous fluid enclosed in a delicate transparent
membrane, the hyaloid membrane. It has been supposed, by Hannover, that from its surface numerous thin lamellae are
prolonged inward in a radiating manner, forming spaces in which the fluid is contained. In the adult, these lamellae cannot
be detected even after careful microscopic examination in the fresh state, but in preparations hardened in weak chromic
acid it is possible to make out a distinct lamellation at the periphery of the body. In the center of the vitreous body, running
from the entrance of the optic nerve to the posterior surface of the lens, is a canal, the hyaloid canal, filled with lymph and
lined by a prolongation of the hyaloid membrane. This canal, in the embryonic vitreous body, conveyed the arteria hyaloidea from the central artery of the retina to the back of the lens. The fluid from the vitreous body is nearly pure water; it
contains, however, some salts, and a little albumin.
The hyaloid membrane envelopes the vitreous body. The portion in front of the ora serrata is thickened by the accession of radial fibers and is termed the zonula ciliaris (zonule of Zinn). Here it presents a series of radially arranged furrows, in which the ciliary processes are accommodated and to which they adhere, as is shown by the fact that when they are
removed some of their pigment remains attached to the zonula. The zonula ciliaris splits into two layers, one of which is
thin and lines the hyaloid fossa; the other is named the suspensory ligament of the lens: it is thicker, and passes over the
ciliary body to be attached to the capsule of the lens a short distance in front of its equator. Scattered and delicate fibers are
also attached to the region of the equator itself. This ligament retains the lens in position, and is relaxed by the contraction
of the meridional fibers of the Ciliaris muscle, so that the lens is allowed to become more convex. Behind the suspensory
ligament there is a sacculated canal, the spatia zonularis (canal of Petit), which encircles the equator of the lens; it can be
easily inflated through a fine blowpipe inserted under the suspensory ligament.
No bloodvessels penetrate the vitreous body, so that its nutrition must be carried on by vessels of the retina and ciliary processes, situated upon its exterior.
The Crystalline Lens (lens crystallina).—The crystalline lens, enclosed in its capsule, is situated immediately behind the iris, in front of the vitreous body, and encircled by the ciliary processes, which slightly overlap its margin.
The capsule of the lens (capsula lentis) is a transparent, structureless membrane which closely surrounds the lens,
and is thicker in front than behind. It is brittle but highly elastic, and when ruptured the edges roll up with the outer surface
innermost. It rests, behind, in the hyaloid fossa in the forepart of the vitreous body; in front, it is in contact with the free
border of the iris, but recedes from it at the circumference, thus forming the posterior chamber of the eye; it is retained in
its position chiefly by the suspensory ligament of the lens, already described.
The lens is a transparent, biconvex body, the convexity of its anterior being less than that of its posterior surface.
The central points of these surfaces are termed respectively the anterior and posterior poles; a line connecting the poles
constitutes the axis of the lens, while the marginal circumference is termed the equator.
Structure.—The lens is made up of soft cortical substance and a firm, central part, the nucleus. Faint lines (radii
lentis) radiate from the poles to the equator. In the adult there may be six or more of these lines, but in the fetus they are
only three in number and diverge from each other at angles of 120 on the anterior surface one line ascends vertically and
the other two diverge downward; on the posterior surface one ray descends vertically and the other two diverge upward.
They correspond with the free edges of an equal number of septa composed of an amorphous substance, which dip into the
substance of the lens. When the lens has been hardened it is seen to consist of a series of concentrically arranged laminae,
each of which is interrupted at the septa referred to. Each lamina is built up of a number of hexagonal, ribbon-like lens fibers, the edges of which are more or less serrated—the serrations fitting between those of neighboring fibers, while the
ends of the fibers come into apposition at the septa. The fibers run in a curved manner from the septa on the anterior surface
to those on the posterior surface. No fibers pass from pole to pole; they are arranged in such a way that those which begin
near the pole on one surface of the lens end near the peripheral extremity of the plane on the other, and vice versa. The fibers of the outer layers of the lens are nucleated, and together form a nuclear layer, most distinct toward the equator. The
anterior surface of the lens is covered by a layer of transparent, columnar, nucleated epithelium. At the equator the cells
become elongated, and their gradual transition into lens fibers can be traced
In the fetus, the lens is nearly spherical, and has a slightly reddish tint; it is soft and breaks down readily on the
slightest pressure. A small branch from the arteria centralis retinae runs forward, as already mentioned, through the vitreous
body to the posterior part of the capsule of the lens, where its branches radiate and form a plexiform network, which covers
the posterior surface of the capsule, and they are continuous around the margin of the capsule with the vessels of the pupillary membrane, and with those of the iris. In the adult, the lens is colorless, transparent, firm in texture, and devoid of vessels. In old age it becomes flattened on both surfaces, slightly opaque, of an amber tint, and increased in density.
Vessels and Nerves.—The arteries of the bulb of the eye are the long, short, and anterior ciliary arteries, and the arteria centralis retinae. They have already been described.
The ciliary veins are seen on the outer surface of the choroid, and are named, from their arrangement, the venae
vorticosae; they converge to four or five equidistant trunks which pierce the sclera midway between the sclero-corneal
junction and the porus opticus. Another set of veins accompanies the anterior ciliary arteries. All of these veins open into
the ophthalmic veins.
The ciliary nerves are derived from the nasociliary nerve and from the ciliary ganglion.
Practice skills
Students are supposed to identify the following structures on the samples:
Eyeball
- ciliary body
- Fibrous layer of eyeball
- iris
- sclera
- pupil
- cornea
- retina
- vascular layer of eyeball
- lens
- choroid
- vitreous body
Practice class 7. The structure of the internal ear. The conducting tracts of the organs of hearing
and equilibrium.
The aim: to learn the structure of the internal ear; to learn the conducting tracts of hearing and equilibrium..
Professional orientation: the knowledge of this topic is necessary for doctors of all specialities; it represents special interest for otorhinolaryngologists, audiologists, neuropathologists and others.
The plan of the practice class:
A. Checking of the home assignment: oral quiz or written test control – 30 minutes.
B. Summary lecture on the topic by teacher – 30 minutes.
a) The development of the ear.
b) The external ear.
c) The middle ear
d) The internal ear.
C. Students’ self-taught time – 55 minutes
D. Home-task – 5 minutes
The Organ of Hearing (Organon Auditus; The Ear)
The ear, or organ of hearing, is divisible into three parts: the external ear, the middle ear or tympanic cavity, and
the internal ear or labyrinth.
The Development of the Ear.—The first rudiment of the internal ear appears shortly after that of the eye, in the
form of a patch of thickened ectoderm, the auditory plate, over the region of the hind-brain. The auditory plate becomes
depressed and converted into the auditory pit. The mouth of the pit is then closed, and thus a shut sac, the auditory vesicle, is formed from it the epithelial lining of the membranous labyrinth is derived. The vesicle becomes pear-shaped, and
the neck of the flask is obliterated. From the vesicle certain diverticula are given off which form the various parts of the
membranous labyrinth. One from the middle part forms the ductus and saccus endolymphaticus, another from the anterior
end gradually elongates, and, forming a tube coiled on itself, becomes the cochlear duct, the vestibular extremity of which
is subsequently constricted to form the canalis reuniens. Three others appear as disk-like evaginations on the surface of the
vesicle; the central parts of the walls of the disks coalesce and disappear, while the peripheral portions persist to form the
semicircular ducts; of these the superior is the first and the lateral the last to be completed. The central part of the vesicle
represents the membranous vestibule, and is subdivided by a constriction into a smaller ventral part, the saccule, and a larger dorsal and posterior part, the utricle. This subdivision is effected by a fold which extends deeply into the proximal part of
the ductus endolymphaticus, with the result that the utricle and saccule ultimately communicate with each other by means
of a Y-shaped canal. The saccule opens into the cochlear duct, through the canalis reuniens, and the semicircular ducts
communicate with the utricle.
The middle ear and auditory tube are developed from the first pharyngeal pouch. The entodermal lining of the
dorsal end of this pouch is in contact with the ectoderm of the corresponding pharyngeal groove; by the extension of the
mesoderm between these two layers the tympanic membrane is formed. During the sixth or seventh month the tympanic
antrum appears as an upward and backward expansion of the tympanic cavity. With regard to the exact mode of develop-
ment of the ossicles of the middle ear there is some difference of opinion. The view generally held is that the malleus is
developed from the proximal end of the mandibular (Meckel’s) cartilage, the incus in the proximal end of the mandibular
arch, and that the stapes is formed from the proximal end of the hyoid arch. The malleus, with the exception of its anterior
process is ossified from a single center which appears near the neck of the bone; the anterior process is ossified separately
in membrane and joins the main part of the bone about the sixth month of fetal life. The incus is ossified from one center
which appears in the upper part of its long crus and ultimately extends into its lenticular process. The stapes first appears as
a ring (annulus stapedius) encircling a small vessel, the stapedial artery, which subsequently undergoes atrophy; it is ossified from a single center which appears in its base.
The external acoustic meatus is developed from the first branchial groove. The lower part of this groove extends
inward as a funnel-shaped tube (primary meatus) from which the cartilaginous portion and a small part of the roof of the
osseous portion of the meatus are developed. From the lower part of the funnel-shaped tube an epithelial lamina extends
downward and inward along the inferior wall of the primitive tympanic cavity; by the splitting of this lamina the inner part
of the meatus (secondary meatus) is produced, while the inner portion of the lamina forms the cutaneous stratum of the
tympanic membrane. The auricula or pinna is developed by the gradual differentiation of tubercles which appear around
the margin of the first branchial groove. The rudiment of the acoustic nerve appears about the end of the third week as a
group of ganglion cells closely applied to the cephalic edge of the auditory vesicle. Whether these cells are derived from
the ectoderm adjoining the auditory vesicle, or have migrated from the wall of the neural tube, is as yet uncertain. The ganglion gradually splits into two parts, the vestibular ganglion and the spiral ganglion. The peripheral branches of the vestibular ganglion pass in two divisions, the pars superior giving rami to the superior ampulla of the superior semicircular
duct, to the lateral ampulla and to the utricle; and the pars inferior giving rami to the saccule and the posterior ampulla. The
proximal fibers of the vestibular ganglion form the vestibular nerve; the proximal fibers of the spiral ganglion form the
cochlear nerve.
The External Ear
The external ear consists of the expanded portion named the auricula or pinna, and the external acoustic meatus.
The former projects from the side of the head and serves to collect the vibrations of the air by which sound is produced; the
latter leads inward from the bottom of the auricula and conducts the vibrations to the tympanic cavity.
The Auricula or Pinna is of an ovoid form, with its larger end directed upward. Its lateral surface is irregularly concave, directed slightly forward, and presents numerous eminences and depressions to which names have been assigned. The
prominent rim of the auricula is called the helix; where the helix turns downward behind, a small tubercle, the auricular
tubercle of Darwin, is frequently seen; this tubercle is very evident about the sixth month of fetal life when the whole auricula has a close resemblance to that of some of the adult monkeys. Another curved prominence, parallel with and in front
of the helix, is called the antihelix; this divides above into two crura, between which is a triangular depression, the fossa
triangularis. The narrow-curved depression between the helix and the antihelix is called the scapha; the antihelix describes a curve around a deep, capacious cavity, the concha, which is partially divided into two parts by the crus or commencement of the helix; the upper part is termed the cymba conchae, the lower part the cavum conchae. In front of the
concha, and projecting backward over the meatus, is a small pointed eminence, the tragus, so called from its being generally covered on its under surface with a tuft of hair, resembling a goat’s beard. Opposite the tragus, and separated from it by
the intertragic notch, is a small tubercle, the antitragus. Below this is the lobule, composed of tough areolar and adipose
tissues, and wanting the firmness and elasticity of the rest of the auricula.
The cranial surface of the auricula presents elevations which correspond to the depressions on its lateral surface and
after which they are named, e. g., eminentia conchae, eminentia triangularis, etc.
Structure.—The auricula is composed of a thin plate of yellow fibrocartilage, covered with integument, and connected to the surrounding parts by ligaments and muscles; and to the commencement of the external acoustic meatus by
fibrous tissue.
The skin is thin, closely adherent to the cartilage, and covered with fine hairs furnished with sebaceous glands,
which are most numerous in the concha and scaphoid fossa. On the tragus and antitragus the hairs are strong and numerous.
The skin of the auricula is continuous with that lining the external acoustic meatus.
The cartilage of the auricula (cartilago auriculae; cartilage of the pinna) consists of a single piece; it gives form to
this part of the ear, and upon its surface are found the eminences and depressions above described. It is absent from the
lobule; it is deficient, also, between the tragus and beginning of the helix, the gap being filled up by dense fibrous tissue. At
the front part of the auricula, where the helix bends upward, is a small projection of cartilage, called the spina helicis, while
in the lower part of the helix the cartilage is prolonged downward as a tail-like process, the cauda helicis; this is separated
from the antihelix by a fissure, the fissura antitragohelicina. The cranial aspect of the cartilage exhibits a transverse furrow, the sulcus antihelicis transversus, which corresponds with the inferior crus of the antihelix and separates the eminentia conchae from the eminentia triangularis. The eminentia conchae is crossed by a vertical ridge (ponticulus), which
gives attachment to the Auricularis posterior muscle. In the cartilage of the auricula are two fissures, one behind the crus
helicis and another in the tragus.
The ligaments of the auricula (ligamenti auricularia [Valsalva]; ligaments of the pinna) consist of two sets: (1) extrinsic, connecting it to the side of the head; (2) intrinsic, connecting various parts of its cartilage together.
The extrinsic ligaments are two in number, anterior and posterior. The anterior ligament extends from the tragus
and spina helicis to the root of the zygomatic process of the temporal bone. The posterior ligament passes from the posterior surface of the concha to the outer surface of the mastoid process.
The chief intrinsic ligaments are: (a) a strong fibrous band, stretching from the tragus to the commencement of the
helix, completing the meatus in front, and partly encircling the boundary of the concha; and (b) a band between the antihelix and the cauda helicis. Other less important bands are found on the cranial surface of the pinna.
The muscles of the auricula consist of two sets: (1) the extrinsic, which connect it with the skull and scalp and
move the auricula as a whole; and (2) the intrinsic, which extend from one part of the auricle to another.
The extrinsic muscles are the Auriculares anterior, superior, and posterior.
The Auricularis anterior (Attrahens aurem), the smallest of the three, is thin, fan-shaped, and its fibers are pale and
indistinct. It arises from the lateral edge of the galea aponeurotica, and its fibers converge to be inserted into a projection
on the front of the helix.
The Auricularis superior (Attolens aurem), the largest of the three, is thin and fan-shaped. Its fibers arise from the
galea aponeurotica, and converge to be inserted by a thin, flattened tendon into the upper part of the cranial surface of the
auricula.
The Auricularis posterior (Retrahens aurem) consists of two or three fleshy fasciculi, which arise from the mastoid
portion of the temporal bone by short aponeurotic fibers. They are inserted into the lower part of the cranial surface of the
concha.
Actions.—In man, these muscles possess very little action: the Auricularis anterior draws the auricula forward and
upward; the Auricularis superior slightly raises it; and the Auricularis posterior draws it backward.
The intrinsic muscles are the:
Helicis major, Antitragicus, Helicis minor, Transversus auriculae, Tragicus, Obliquus auriculae. The Helicis major
is a narrow vertical band situated upon the anterior margin of the helix. It arises below, from the spina helicis, and is inserted into the anterior border of the helix, just where it is about to curve backward. The Helicis minor is an oblique fasciculus,
covering the crus helicis. The Tragicus is a short, flattened vertical band on the lateral surface of the tragus. The Antitragicus arises from the outer part of the antitragus, and is inserted into the cauda helicis and antihelix. The Transversus auriculae is placed on the cranial surface of the pinna. It consists of scattered fibers, partly tendinous and partly muscular, extending from the eminentia conchae to the prominence corresponding with the scapha. The Obliquus auriculae, also on the cranial surface, consists of a few fibers extending from the upper and back part of the concha to the convexity immediately
above it.
Nerves.—The Auriculares anterior and superior and the intrinsic muscles on the lateral surface are supplied by the
temporal branch of the facial nerve, the Auricularis posterior and the intrinsic muscles on the cranial surface by the posterior auricular branch of the same nerve.
The arteries of the auricula are the posterior auricular from the external carotid, the anterior auricular from the superficial temporal, and a branch from the occipital artery.
The veins accompany the corresponding arteries.
The sensory nerves are: the great auricular, from the cervical plexus; the auricular branch of the vagus; the auriculotemporal branch of the mandibular nerve; and the lesser occipital from the cervical plexus.
The External Acoustic Meatus (meatus acusticus externus; external auditory canal or meatus) extends from the
bottom of the concha to the tympanic membrane. It is about 4 cm. in length if measured from the tragus; from the bottom of
the concha its length is about 2.5 cm. It forms an S-shaped curve, and is directed at first inward, forward, and slightly upward (pars externa); it then passes inward and backward (pars media), and lastly is carried inward, forward, and slightly
downward (pars interna). It is an oval cylindrical canal, the greatest diameter being directed downward and backward at
the external orifice, but nearly horizontally at the inner end. It presents two constrictions, one near the inner end of the cartilaginous portion, and another, the isthmus, in the osseous portion, about 2 cm. from the bottom of the concha. The tympanic membrane, which closes the inner end of the meatus, is obliquely directed; in consequence of this the floor and anterior wall of the meatus are longer than the roof and posterior wall.
The external acoustic meatus is formed partly by cartilage and membrane, and partly by bone, and is lined by skin.
The cartilaginous portion (meatus acusticus externus cartilagineus) is about 8 mm. in length; it is continuous with
the cartilage of the auricula, and firmly attached to the circumference of the auditory process of the temporal bone. The
cartilage is deficient at the upper and back part of the meatus, its place being supplied by fibrous membrane; two or three
deep fissures are present in the anterior part of the cartilage.
The osseous portion (meatus acusticus externus osseus) is about 16 mm. in length, and is narrower than the cartilaginous portion. It is directed inward and a little forward, forming in its course a slight curve the convexity of which is
upward and backward. Its inner end is smaller than the outer, and sloped, the anterior wall projecting beyond the posterior
for about 4 mm.; it is marked, except at its upper part, by a narrow groove, the tympanic sulcus, in which the circumference of the tympanic membrane is attached. Its outer end is dilated and rough in the greater part of its circumference, for
the attachment of the cartilage of the auricula. The front and lower parts of the osseous portion are formed by a curved plate
of bone, the tympanic part of the temporal, which, in the fetus, exists as a separate ring (annulus tympanicus,) incomplete
at its upper part.
The skin lining the meatus is very thin; adheres closely to the cartilaginous and osseous portions of the tube, and
covers the outer surface of the tympanic membrane. After maceration, the thin pouch of epidermis, when withdrawn, preserves the form of the meatus. In the thick subcutaneous tissue of the cartilaginous part of the meatus are numerous ceruminous glands, which secrete the ear-wax; their structure resembles that of the sudoriferous glands.
Relations of the Meatus.—In front of the osseous part is the condyle of the mandible, which however, is frequently
separated from the cartilaginous part by a portion of the parotid gland. The movements of the jaw influence to some extent
the lumen of this latter portion. Behind the osseous part are the mastoid air cells, separated from the meatus by a thin layer
of bone.
The arteries supplying the meatus are branches from the posterior auricular, internal maxillary, and temporal.
The nerves are chiefly derived from the auriculotemporal branch of the mandibular nerve and the auricular branch
of the vagus.
The Middle Ear or Tympanic Cavity (Cavum Tympani; Drum; Tympanum)
The middle ear or tympanic cavity is an irregular, laterally compressed space within the temporal bone. It is filled
with air, which is conveyed to it from the nasal part of the pharynx through the auditory tube. It contains a chain of movable bones, which connect its lateral to its medial wall, and serve to convey the vibrations communicated to the tympanic
membrane across the cavity to the internal ear.
The tympanic cavity consists of two parts: the tympanic cavity proper, opposite the tympanic membrane, and the
attic or epitympanic recess, above the level of the membrane; the latter contains the upper half of the malleus and the
greater part of the incus. Including the attic, the vertical and antero-posterior diameters of the cavity are each about 15 mm.
The transverse diameter measures about 6 mm. above and 4 mm. below; opposite the center of the tympanic membrane it is
only about 2 mm. The tympanic cavity is bounded laterally by the tympanic membrane; medially, by the lateral wall of the
internal ear; it communicates, behind, with the tympanic antrum and through it with the mastoid air cells, and in front with
the auditory tube.
The Tegmental Wall or Roof (paries tegmentalis) is formed by a thin plate of bone, the tegmen tympani, which
separates the cranial and tympanic cavities. It is situated on the anterior surface of the petrous portion of the temporal bone
close to its angle of junction with the squama temporalis; it is prolonged backward so as to roof in the tympanic antrum,
and forward to cover in the semicanal for the Tensor tympani muscle. Its lateral edge corresponds with the remains of the
petrosquamous suture.
The Jugular Wall or Floor (paries jugularis) is narrow, and consists of a thin plate of bone (fundus tympani)
which separates the tympanic cavity from the jugular fossa. It presents, near the labyrinthic wall, a small aperture for the
passage of the tympanic branch of the glossopharyngeal nerve.
The Membranous or Lateral Wall (paries membranacea; outer wall) is formed mainly by the tympanic membrane, partly by the ring of bone into which this membrane is inserted. This ring of bone is incomplete at its upper part,
forming a notch (notch of Rivinus), close to which are three small apertures: the iter chordae posterius, the petrotympanic fissure, and the iter chordae anterius.
The iter chordae posterius (apertura tympanica canaliculi chordae) is situated in the angle of junction between the
mastoid and membranous wall of the tympanic cavity immediately behind the tympanic membrane and on a level with the
upper end of the manubrium of the malleus; it leads into a minute canal, which descends in front of the canal for the facial
nerve, and ends in that canal near the stylo-mastoid foramen. Through it the chorda tympani nerve enters the tympanic
cavity.
The petrotympanic fissure (fissura petrotympanica; Glaserian fissure) opens just above and in front of the ring of
bone into which the tympanic membrane is inserted; in this situation it is a mere slit about 2 mm. in length. It lodges the
anterior process and anterior ligament of the malleus, and gives passage to the anterior tympanic branch of the internal
maxillary artery.
The iter chordae anterius (canal of Huguier) is placed at the medial end of the petrotympanic fissure; through it
the chorda tympani nerve leaves the tympanic cavity.
The Tympanic Membrane (membrana tympani) separates the tympanic cavity from the bottom of the external
acoustic meatus. It is a thin, semitransparent membrane, nearly oval in form, somewhat broader above than below, and directed very obliquely downward and inward so as to form an angle of about fifty-five degrees with the floor of the meatus.
Its longest diameter is downward and forward, and measures from 9 to 10 mm.; its shortest diameter measures from 8 to 9
mm. The greater part of its circumference is thickened, and forms a fibrocartilaginous ring which is fixed in the tympanic
sulcus at the inner end of the meatus. This sulcus is deficient superiorly at the notch of Rivinus, and from the ends of this
notch two bands, the anterior and posterior malleolar folds, are prolonged to the lateral process of the malleus. The
small, somewhat triangular part of the membrane situated above these folds is lax and thin, and is named the pars flaccida;
in it a small orifice is sometimes seen. The manubrium of the malleus is firmly attached to the medial surface of the membrane as far as its center, which it draws toward the tympanic cavity; the lateral surface of the membrane is thus concave,
and the most depressed part of this concavity is named the umbo.
Structure.—The tympanic membrane is composed of three strata: a lateral (cutaneous), an intermediate (fibrous),
and a medial (mucous). The cutaneous stratum is derived from the integument lining the meatus. The fibrous stratum
consists of two layers: a radiate stratum, the fibers of which diverge from the manubrium of the malleus, and a circular stratum, the fibers of which are plentiful around the circumference but sparse and scattered near the center of the membrane.
Branched or dendritic fibers, as pointed out by Grüber, are also present especially in the posterior half of the membrane.
Vessels and Nerves.—The arteries of the tympanic membrane are derived from the deep auricular branch of the internal maxillary, which ramifies beneath the cutaneous stratum; and from the stylomastoid branch of the posterior auricular,
and tympanic branch of the internal maxillary, which are distributed on the mucous surface. The superficial veins open into
the external jugular; those on the deep surface drain partly into the transverse sinus and veins of the dura mater, and partly
into a plexus on the auditory tube. The membrane receives its chief nerve supply from the auriculotemporal branch of the
mandibular; the auricular branch of the vagus, and the tympanic branch of the glossopharyngeal also supply it.
The Labyrinthic or Medial Wall (paries labyrinthica; inner wall) is vertical in direction, and presents for examination the fenestrae vestibuli and cochleae, the promontory, and the prominence of the facial canal.
The fenestra vestibuli (fenestra ovalis) is a reniform opening leading from the tympanic cavity into the vestibule of
the internal ear; its long diameter is horizontal, and its convex border is upward. In the recent state it is occupied by the
base of the stapes, the circumference of which is fixed by the annular ligament to the margin of the foramen.
The fenestra cochleae (fenestra rotunda) is situated below and a little behind the fenestra vestibuli, from which it is
separated by a rounded elevation, the promontory. It is placed at the bottom of a funnel-shaped depression and, in the
macerated bone, leads into the cochlea of the internal ear; in the fresh state it is closed by a membrane, the secondary tym-
panic membrane, which is concave toward the tympanic cavity, convex toward the cochlea. This membrane consists of
three layers: an external, or mucous, derived from the mucous lining of the tympanic cavity; an internal, from the lining
membrane of the cochlea; and an intermediate, or fibrous layer.
The promontory (promontorium) is a rounded hollow prominence, formed by the projection outward of the first
turn of the cochlea; it is placed between the fenestrae, and is furrowed on its surface by small grooves, for the lodgement of
branches of the tympanic plexus. A minute spicule of bone frequently connects the promontory to the pyramidal eminence.
The prominence of the facial canal (prominentia canalis facialis; prominence of aqueduct of Fallopius) indicates
the position of the bony canal in which the facial nerve is contained; this canal traverses the labyrinthic wall of the tympanic cavity above the fenestra vestibuli, and behind that opening curves nearly vertically downward along the mastoid wall.
The mastoid or posterior wall (paries mastoidea) is wider above than below, and presents for examination the entrance to the tympanic antrum, the pyramidal eminence, and the fossa incudis.
The entrance to the antrum is a large irregular aperture, which leads backward from the epitympanic recess into a
considerable air space, named the tympanic or mastoid antrum. The antrum communicates behind and below with the
mastoid air cells, which vary considerably in number, size, and form; the antrum and mastoid air cells are lined by mucous
membrane, continuous with that lining the tympanic cavity. On the medial wall of the entrance to the antrum is a rounded
eminence, situated above and behind the prominence of the facial canal; it corresponds with the position of the ampullated
ends of the superior and lateral semicircular canals.
The pyramidal eminence (eminentia pyramidalis; pyramid) is situated immediately behind the fenestra vestibuli,
and in front of the vertical portion of the facial canal; it is hollow, and contains the Stapedius muscle; its summit projects
forward toward the fenestra vestibuli, and is pierced by a small aperture which transmits the tendon of the muscle. The cavity in the pyramidal eminence is prolonged downward and backward in front of the facial canal, and communicates with it
by a minute aperture which transmits a twig from the facial nerve to the Stapedius muscle.
The fossa incudis is a small depression in the lower and back part of the epitympanic recess; it lodges the short crus
of the incus.
The Carotid or Anterior Wall (paries carotica) is wider above than below; it corresponds with the carotid canal,
from which it is separated by a thin plate of bone perforated by the tympanic branch of the internal carotid artery, and by
the deep petrosal nerve which connects the sympathetic plexus on the internal carotid artery with the tympanic plexus on
the promontory. At the upper part of the anterior wall are the orifice of the semicanal for the Tensor tympani muscle and
the tympanic orifice of the auditory tube, separated from each other by a thin horizontal plate of bone, the septum canalis
musculotubarii. These canals run from the tympanic cavity forward and downward to the retiring angle between the
squama and the petrous portion of the temporal bone.
The semicanal for the Tensor tympani (semicanalis m. tensoris tympani) is the superior and the smaller of the
two; it is cylindrical and lies beneath the tegmen tympani. It extends on to the labyrinthic wall of the tympanic cavity and
ends immediately above the fenestra vestibuli.
The septum canalis musculotubarii (processus cochleariformis) passes backward below this semicanal, forming
its lateral wall and floor; it expands above the anterior end of the fenestra vestibuli and terminates there by curving laterally
so as to form a pulley over which the tendon of the muscle passes.
The auditory tube (tuba auditiva; Eustachian tube) is the channel through which the tympanic cavity communicates with the nasal part of the pharynx. Its length is about 36 mm., and its direction is downward, forward, and medialward, forming an angle of about 45 degrees with the sagittal plane and one of from 30 to 40 degrees with the horizontal
plane. It is formed partly of bone, partly of cartilage and fibrous tissue.
The osseous portion (pars osseo tubae auditivae) is about 12 mm. in length. It begins in the carotid wall of the
tympanic cavity, below the septum canalis musculotubarii, and, gradually narrowing, ends at the angle of junction of the
squama and the petrous portion of the temporal bone, its extremity presenting a jagged margin which serves for the attachment of the cartilaginous portion.
The cartilaginous portion (pars cartilaginea tubae auditivae), about 24 mm. in length, is formed of a triangular
plate of elastic fibrocartilage, the apex of which is attached to the margin of the medial end of the osseous portion of the
tube, while its base lies directly under the mucous membrane of the nasal part of the pharynx, where it forms an elevation,
the torus tubarius or cushion, behind the pharyngeal orifice of the tube. The upper edge of the cartilage is curled upon
itself, being bent laterally so as to present on transverse section the appearance of a hook; a groove or furrow is thus produced, which is open below and laterally, and this part of the canal is completed by fibrous membrane. The cartilage lies in
a groove between the petrous part of the temporal and the great wing of the sphenoid; this groove ends opposite the middle
of the medial pterygoid plate. The cartilaginous and bony portions of the tube are not in the same plane, the former inclining downward a little more than the latter. The diameter of the tube is not uniform throughout, being greatest at the pharyngeal orifice, least at the junction of the bony and cartilaginous portions, and again increased toward the tympanic cavity; the
narrowest part of the tube is termed the isthmus. The position and relations of the pharyngeal orifice are described with the
nasal part of the pharynx. The mucous membrane of the tube is continuous in front with that of the nasal part of the pharynx, and behind with that of the tympanic cavity; it is covered with ciliated epithelium and is thin in the osseous portion,
while in the cartilaginous portion it contains many mucous glands and near the pharyngeal orifice a considerable amount of
adenoid tissue, which has been named by Gerlach the tube tonsil. The tube is opened during deglutition by the Salpingopharyngeus and Dilatator tubae. The latter arises from the hook of the cartilage and from the membranous part of the
tube, and blends below with the Tensor veli palatini.
The Internal Ear or Labyrinth (Auris Interna)
The internal ear is the essential part of the organ of hearing, receiving the ultimate distribution of the auditory
nerve. It is called the labyrinth, from the complexity of its shape, and consists of two parts: the osseous labyrinth, a series
of cavities within the petrous part of the temporal bone, and the membranous labyrinth, a series of communicating membranous sacs and ducts, contained within the bony cavities.
The Osseous Labyrinth (labyrinthus osseus)—The osseous labyrinth consists of three parts: the vestibule, semicircular canals, and cochlea. These are cavities hollowed out of the substance of the bone, and lined by periosteum; they
contain a clear fluid, the perilymph, in which the membranous labyrinth is situated.
The Vestibule (vestibulum).—The vestibule is the central part of the osseous labyrinth, and is situated medial to the
tympanic cavity, behind the cochlea, and in front of the semicircular canals. It is somewhat ovoid in shape, but flattened
transversely; it measures about 5 mm. from before backward, the same from above downward, and about 3 mm. across. In
its lateral or tympanic wall is the fenestra vestibuli, closed, in the fresh state, by the base of the stapes and annular ligament. On its medial wall, at the forepart, is a small circular depression, the recessus sphaericus, which is perforated, at its
anterior and inferior part, by several minute holes (macula cribrosa media) for the passage of filaments of the acoustic
nerve to the saccule; and behind this depression is an oblique ridge, the crista vestibuli, the anterior end of which is named
the pyramid of the vestibule. This ridge bifurcates below to enclose a small depression, the fossa cochlearis, which is
perforated by a number of holes for the passage of filaments of the acoustic nerve which supply the vestibular end of the
ductus cochlearis. As the hinder part of the medial wall is the orifice of the aquaeductus vestibuli, which extends to the
posterior surface of the petrous portion of the temporal bone. It transmits a small vein, and contains a tubular prolongation
of the membranous labyrinth, the ductus endolymphaticus, which ends in a cul-de-sac between the layers of the dura mater within the cranial cavity. On the upper wall or roof is a transversely oval depression, the recessus ellipticus, separated
from the recessus sphaericus by the crista vestibuli already mentioned. The pyramid and adjoining part of the recessus ellipticus are perforated by a number of holes (macula cribrosa superior). The apertures in the pyramid transmit the nerves
to the utricle; those in the recessus ellipticus the nerves to the ampullae of the superior and lateral semicircular ducts. Behind are the five orifices of the semicircular canals. In front is an elliptical opening, which communicates with the scala
vestibuli of the cochlea.
The Bony Semicircular Canals (canales semicirculares ossei).—The bony semicircular canals are three in number, superior, posterior, and lateral, and are situated above and behind the vestibule. They are unequal in length, compressed from side to side, and each describes the greater part of a circle. Each measures about 0.8 mm. in diameter, and
presents a dilatation at one end, called the ampulla, which measures more than twice the diameter of the tube. They open
into the vestibule by five orifices, one of the apertures being common to two of the canals.
The superior semicircular canal (canalis semicircularis superior), 15 to 20 mm. in length, is vertical in direction,
and is placed transversely to the long axis of the petrous portion of the temporal bone, on the anterior surface of which its
arch forms a round projection. It describes about two-thirds of a circle. Its lateral extremity is ampullated, and opens into
the upper part of the vestibule; the opposite end joins with the upper part of the posterior canal to form the crus commune,
which opens into the upper and medial part of the vestibule.
The posterior semicircular canal (canalis semicircularis posterior), also vertical, is directed backward, nearly parallel to the posterior surface of the petrous bone; it is the longest of the three, measuring from 18 to 22 mm.; its lower or
ampullated end opens into the lower and back part of the vestibule, its upper into the crus commune already mentioned
The lateral or horizontal canal (canalis semicircularis lateralis; external semicircular canal) is the shortest of the
three. It measures from 12 to 15 mm., and its arch is directed horizontally backward and lateralward; thus each semicircular
canal stands at right angles to the other two. Its ampullated end corresponds to the upper and lateral angle of the vestibule,
just above the fenestra vestibuli, where it opens close to the ampullated end of the superior canal; its opposite end opens at
the upper and back part of the vestibule. The lateral canal of one ear is very nearly in the same plane as that of the other;
while the superior canal of one ear is nearly parallel to the posterior canal of the other..
The Cochlea—The cochlea bears some resemblance to a common snail-shell; it forms the anterior part of the labyrinth, is conical in form, and placed almost horizontally in front of the vestibule; its apex (cupula) is directed forward and
lateralward, with a slight inclination downward, toward the upper and front part of the labyrinthic wall of the tympanic cavity; its base corresponds with the bottom of the internal acoustic meatus, and is perforated by numerous apertures for the
passage of the cochlear division of the acoustic nerve. It measures about 5 mm. from base to apex, and its breadth across
the base is about 9 mm. It consists of a conical shaped central axis, the modiolus; of a canal, the inner wall of which is
formed by the central axis, wound spirally around it for two turns and three-quarters, from the base to the apex; and of a
delicate lamina, the osseous spiral lamina, which projects from the modiolus, and, following the windings of the canal,
partially subdivides it into two. In the recent state a membrane, the basilar membrane, stretches from the free border of
this lamina to the outer wall of the bony cochlea and completely separates the canal into two passages, which, however,
communicate with each other at the apex of the modiolus by a small opening named the helicotrema.
The modiolus is the conical central axis or pillar of the cochlea. Its base is broad, and appears at the bottom of the
internal acoustic meatus, where it corresponds with the area cochleae; it is perforated by numerous orifices, which transmit
filaments of the cochlear division of the acoustic nerve; the nerves for the first turn and a half pass through the foramina of
the tractus spiralis foraminosus; those for the apical turn, through the foramen centrale. The canals of the tractus spiralis
foraminosus pass up through the modiolus and successively bend outward to reach the attached margin of the lamina spiralis ossea. Here they become enlarged, and by their apposition form the spiral canal of the modiolus, which follows the
course of the attached margin of the osseous spiral lamina and lodges the spiral ganglion (ganglion of Corti). The foramen
centrale is continued into a canal which runs up the middle of the modiolus to its apex. The modiolus diminishes rapidly in
size in the second and succeeding coil.
The bony canal of the cochlea takes two turns and three-quarters around the modiolus. It is about 30 mm. in length,
and diminishes gradually in diameter from the base to the summit, where it terminates in the cupula, which forms the apex
of the cochlea. The beginning of this canal is about 3 mm. in diameter; it diverges from the modiolus toward the tympanic
cavity and vestibule, and presents three openings. One, the fenestra cochleae, communicates with the tympanic cavity—in
the fresh state this aperture is closed by the secondary tympanic membrane; another, of an elliptical form, opens into the
vestibule. The third is the aperture of the aquaeductus cochleae, leading to a minute funnel-shaped canal, which opens on
the inferior surface of the petrous part of the temporal bone and transmits a small vein, and also forms a communication
between the subarachnoid cavity and the scala tympani.
The osseous spiral lamina (lamina spiralis ossea) is a bony shelf or ledge which projects from the modiolus into
the interior of the canal, and, like the canal, takes two-and three-quarter turns around the modiolus. It reaches about halfway toward the outer wall of the tube, and partially divides its cavity into two passages or scalae, of which the upper is
named the scala vestibuli, while the lower is termed the scala tympani. Near the summit of the cochlea the lamina ends in
a hook-shaped process, the hamulus laminae spiralis; this assists in forming the boundary of a small opening, the helicotrema, through which the two scalae communicate with each other. From the spiral canal of the modiolus numerous canals
pass outward through the osseous spiral lamina as far as its free edge. In the lower part of the first turn a second bony lamina, the secondary spiral lamina, projects inward from the outer wall of the bony tube; it does not, however, reach the primary osseous spiral lamina, so that if viewed from the vestibule a narrow fissure, the vestibule fissure, is seen between
them.
The osseous labyrinth is lined by an exceedingly thin fibro-serous membrane; its attached surface is rough and fibrous, and closely adherent to the bone; its free surface is smooth and pale, covered with a layer of epithelium, and secretes
a thin, limpid fluid, the perilymph. A delicate tubular process of this membrane is prolonged along the aqueduct of the
cochlea to the inner surface of the dura mater.
The Membranous Labyrinth (labyrinthus membranaceus)—The membranous labyrinth is lodged within the bony
cavities just described, and has the same general form as these; it is, however, considerably smaller, and is partly separated
from the bony walls by a quantity of fluid, the perilymph. In certain places it is fixed to the walls of the cavity. The membranous labyrinth contains fluid, the endolymph, and on its walls the ramifications of the acoustic nerve are distributed.
The Utricle (utriculus).—The utricle, the larger of the two, is of an oblong form, compressed transversely, and occupies the upper and back part of the vestibule, lying in contact with the recessus ellipticus and the part below it. That portion which is lodged in the recess forms a sort of pouch or cul-de-sac, the floor and anterior wall of which are thickened,
and form the macula acustica utriculi, which receives the utricular filaments of the acoustic nerve. The cavity of the utricle communicates behind with the semicircular ducts by five orifices. From its anterior wall is given off the ductus utriculosaccularis, which opens into the ductus endolymphaticus.
The Saccule (sacculus).—The saccule is the smaller of the two vestibular sacs; it is globular in form, and lies in the
recessus sphaericus near the opening of the scala vestibuli of the cochlea. Its anterior part exhibits an oval thickening, the
macula acustica sacculi, to which are distributed the saccular filaments of the acoustic nerve. Its cavity does not directly
communicate with that of the utricle. From the posterior wall a canal, the ductus endolymphaticus, is given off; this duct
is joined by the ductus utriculosaccularis, and then passes along the aquaeductus vestibuli and ends in a blind pouch (saccus endolymphaticus) on the posterior surface of the petrous portion of the temporal bone, where it is in contact with the
dura mater. From the lower part of the saccule a short tube, the canalis reuniens of Hensen, passes downward and opens
into the ductus cochlearis near its vestibular extremity.
The Semicircular Ducts (ductus semicirculares; membranous semicircular canals)—The semicircular ducts are
about one-fourth of the diameter of the osseous canals, but in number, shape, and general form they are precisely similar,
and each presents at one end an ampulla. They open by five orifices into the utricle, one opening being common to the medial end of the superior and the upper end of the posterior duct. In the ampullae the wall is thickened, and projects into the
cavity as a fiddle-shaped, transversely placed elevation, the septum transversum, in which the nerves end.
The utricle, saccule, and semicircular ducts are held in position by numerous fibrous bands which stretch across the
space between them and the bony walls.
Structure—The walls of the utricle, saccule, and semicircular ducts consist of three layers. The outer layer is a
loose and flocculent structure, apparently composed of ordinary fibrous tissue containing bloodvessels and some pigmentcells. The middle layer, thicker and more transparent, forms a homogeneous membrana propria, and presents on its internal
surface, especially in the semicircular ducts, numerous papilliform projections, which, on the addition of acetic acid, exhibit an appearance of longitudinal fibrillation. The inner layer is formed of polygonal nucleated epithelial cells. In the maculae of the utricle and saccule, and in the transverse septa of the ampullae of the semicircular ducts, the middle coat is thickened and the epithelium is columnar, and consists of supporting cells and hair cells. The former are fusiform, and their
deep ends are attached to the membrana propria, while their free extremities are united to form a thin cuticle. The hair cells
are flask-shaped, and their deep, rounded ends do not reach the membrana propria, but lie between the supporting cells. The
deep part of each contains a large nucleus, while its more superficial part is granular and pigmented. The free end is surmounted by a long, tapering, hair-like filament, which projects into the cavity. The filaments of the acoustic nerve enter
these parts, and having pierced the outer and middle layers, they lose their medullary sheaths, and their axis-cylinders ramify between the hair cells.
Two small rounded bodies termed otoconia, each consisting of a mass of minute crystalline grains of carbonate of
lime, held together in a mesh of gelatinous tissue, are suspended in the endolymph in contact wish the free ends of the hairs
projecting from the maculae. According to Bowman, a calcareoutmaterial is also sparingly scattered in the cells lining the
ampullae of the semicircular ducts.
The Ductus Cochlearis (membranous cochlea; scala media).—The ductus cochlearis consists of a spirally arranged tube enclosed in the bony canal of the cochlea and lying along its outer wall.
As already stated, the osseous spiral lamina extends only part of the distance between the modiolus and the outer
wall of the cochlea, while the basilar membrane stretches from its free edge to the outer wall of the cochlea, and com-
pletes the roof of the scala tympani. A second and more delicate membrane, the vestibular membrane (Reissneri) extends
from the thickened periosteum covering the osseous spiral lamina to the outer wall of the cochlea, where it is attached at
some little distance above the outer edge of the basilar membrane. A canal is thus shut off between the scala tympani below
and the scala vestibuli above; this is the ductus cochlearis or scala media. It is triangular on transverse section, its roof
being formed by the vestibular membrane, its outer wall by the periosteum lining the bony canal, and its floor by the membrana basilaris and the outer part of the lamina spiralis ossea. Its extremities are closed; the upper is termed the lagena and
is attached to the cupula at the upper part of the helicotrema; the lower is lodged in the recessus cochlearis of the vestibule.
Near the lower end the ductus cochlearis is brought into continuity with the saccule by a narrow, short canal, the canalis
reuniens of Hensen. On the membrana basilaris is situated the spiral organ of Corti. The vestibular membrane is thin and
homogeneous, and is covered on its upper and under surfaces by a layer of epithelium. The periosteum, forming the outer
wall of the ductus cochlearis, is greatly thickened and altered in character, and is called the spiral ligament. It projects inward below as a triangular prominence, the basilar crest, which gives attachment to the outer edge of the basilar membrane; immediately above the crest is a concavity, the sulcus spiralis externus. The upper portion of the spiral ligament
contains numerous capillary loops and small bloodvessels, and is termed the stria vascularis.
The osseous spiral lamina consists of two plates of bone, and between these are the canals for the transmission of the
filaments of the acoustic nerve. On the upper plate of that part of the lamina which is outside the vestibular membrane, the
periosteum is thickened to form the limbus laminae spiralis, this ends externally in a concavity, the sulcus spiralis internus, which represents, on section, the form of the letter C; the upper part, formed by the overhanging extremity of the limbus, is named the vestibular lip; the lower part, prolonged and tapering, is called the tympanic lip, and is perforated by
numerous foramina for the passage of the cochlear nerves. The upper surface of the vestibular lip is intersected at right angles by a number of furrows, between which are numerous elevations; these present the appearance of teeth along the free
surface and margin of the lip, and have been named by Huschke the auditory teeth. The limbus is covered by a layer of
what appears to be squamous epithelium, but the deeper parts of the cells with their contained nuclei occupy the intervals
between the elevations and between the auditory teeth. This layer of epithelium is continuous on the one hand with that
lining the sulcus spiralis internus, and on the other with that covering the under surface of the vestibular membrane.
Basilar Membrane.—The basilar membrane stretches from the tympanic lip of the osseous spiral lamina to the basilar crest and consists of two parts, an inner and an outer. The inner is thin, and is named the zona arcuata: it supports the
spiral organ of Corti. The outer is thicker and striated, and is termed the zona pectinata. The under surface of the membrane is covered by a layer of vascular connective tissue; one of the vessels in this tissue is somewhat larger than the rest,
and is named the vas spirale; it lies below Corti’s tunnel.
The spiral organ of Corti (organon spirale [Corti]; organ of Corti) is composed of a series of epithelial structures
placed upon the inner part of the basilar membrane. The more central of these structures are two rows of rod-like bodies,
the inner and outer rods or pillars of Corti. The bases of the rods are supported on the basilar membrane, those of the
inner row at some distance from those of the outer; the two rows incline toward each other and, coming into contact above,
enclose between them and the basilar membrane a triangular tunnel, the tunnel of Corti. On the inner side of the inner rods
is a single row of hair cells, and on the outer side of the outer rods three or four rows of similar cells, together with certain
supporting cells termed the cells of Deiters and Hensen. The free ends of the outer hair cells occupy a series of apertures in
a net-like membrane, the reticular membrane, and the entire organ is covered by the tectorial membrane.
RODS OF CORTI.—Each of these consists of a base or foot-plate, and elongated part or body, and an upper end or
head; the body of each rod is finely striated, but in the head there is an oval non-striated portion which stains deeply with
carmine. Occupying the angles between the rods and the basilar membrane are nucleated cells which partly envelop the
rods and extend on to the floor of Corti’s tunnel; these may be looked upon as the undifferentiated parts of the cells from
which the rods have been formed.
The inner rods number nearly 6000, and their bases rest on the basilar membrane close to the tympanic lip of the
sulcus spiralis internus. The shaft or body of each is sinously curved and forms an angle of about 60 degrees with the basilar membrane. The head resembles the proximal end of the ulna and presents a deep concavity which accommodates a convexity on the head of the outer rod. The head-plate, or portion overhanging the concavity, overlaps the head-plate of the
outer rod.
The outer rods, nearly 4000 in number, are longer and more obliquely set than the inner, forming with the basilar
membrane an angle of about 40 degrees. Their heads are convex internally; they fit into the concavities on the heads of the
inner rods and are continued outward as thin flattened plates, termed phalangeal processes, which unite with the phalangeal processes of Deiters’ cells to form the reticular membrane.
Hair Cells.—The hair cells are short columnar cells; their free ends are on a level with the heads of Corti’s rods,
and each is surmounted by about twenty hair-like processes arranged in the form of a crescent with its concavity directed
inward. The deep ends of the cells reach about half-way along Corti’s rods, and each contains a large nucleus; in contact
with the deep ends of the hair cells are the terminal filaments of the cochlear division of the acoustic nerve. The inner hair
cells are arranged in a single row on the medial side of the inner rods, and their diameters being greater than those of the
rods it follows that each hair cell is supported by more than one rod. The free ends of the inner hair cells are encircled by a
cuticular membrane which is fixed to the heads of the inner rods. Adjoining the inner hair cells are one or two rows of columnar supporting cells, which, in turn, are continuous with the cubical cells lining the sulcus spiralis internus. The outer
hair cells number about 12,000, and are nearly twice as long as the inner. In the basal coil of the cochlea they are arranged
in three regular rows; in the apical coil, in four, somewhat irregular, rows.
Between the rows of the outer hair cells are rows of supporting cells, called the cells of Deiters; their expanded bases are planted on the basilar membrane, while the opposite end of each presents a clubbed extremity or phalangeal process. Immediately to the outer side of Deiters’ cells are five or six rows of columnar cells, the supporting cells of Hensen.
Their bases are narrow, while their upper parts are expanded and form a rounded elevation on the floor of the ductus cochlearis. The columnar cells lying outside Hensen’s cells are termed the cells of Claudius. A space exists between the outer
rods of Corti and the adjacent hair cells; this is called the space of Nuel.
The reticular lamina is a delicate frame-work perforated by rounded holes which are occupied by the free ends of
the outer hair cells. It extends from the heads of the outer rods of Corti to the external row of the outer hair cells, and is
formed by several rows of “minute fiddle-shaped cuticular structures,” called phalanges, between which are circular apertures containing the free ends of the hair cells. The inner most row of phalanges consists of the phalangeal processes of the
outer rods of Corti; the outer rows are formed by the modified free ends of Deiters’ cells.
Covering the sulcus spiralis internus and the spiral organ of Corti is the tectorial membrane, which is attached to
the limbus laminae spiralis close to the inner edge of the vestibular membrane. Its inner part is thin and overlies the auditory teeth of Huschke; its outer part is thick, and along its lower surface, opposite the inner hair cells, is a clear band, named
Hensen’s stripe, due to the intercrossing of its fibers. The lateral margin of the membrane is much thinner. Hardesty 151
considers the tectorial membrane as the vibrating mechanism in the cochlea. It is inconceivably delicate and flexible; far
more sensitively flexible in the transverse than in the longitudinal direction and the readiness with which it bends when
touched is beyond description. It is ectodermal in origin. It consists of fine colorless fibers embedded in a transparent matrix (the matrix may be a variety of soft keratin), of a soft collagenous, semisolid character with marked adhesiveness. The
general transverse direction of the fibers inclines from the radius of the cochlea toward the apex.
The acoustic nerve (n. acusticus; auditory nerve or nerve of hearing) divides near the bottom of the internal acoustic meatus into an anterior or cochlear and a posterior or vestibular branch.
The vestibular nerve (n. vestibularis) supplies the utricle, the saccule, and the ampullae of the semicircular ducts.
On the trunk of the nerve, within the internal acoustic meatus, is a ganglion, the vestibular ganglion (ganglion of Scarpa);
the fibers of the nerve arise from the cells of this ganglion. On the distal side of the ganglion the nerve splits into a superior,
an inferior, and a posterior branch. The filaments of the superior branch are transmitted through the foramina in the area
vestibularis superior, and end in the macula of the utricle and in the ampullae of the superior and lateral semicircular ducts;
those of the inferior branch traverse the foramina in the area vestibularis inferior, and end in the macula of the saccule. The
posterior branch runs through the foramen singulare at the postero-inferior part of the bottom of the meatus and divides
into filaments for the supply of the ampulla of the posterior semicircular duct.
The cochlear nerve (n. cochlearis) divides into numerous filaments at the base of the modiolus; those for the basal
and middle coils pass through the foramina in the tractus spiralis foraminosis, those for the apical coil through the canalis
centralis, and the nerves bend outward to pass between the lamellae of the osseous spiral lamina. Occupying the spiral canal of the modiolus is the spiral ganglion of the cochlea (ganglion of Corti), consisting of bipolar nerve cells, which constitute the cells of origin of this nerve. Reaching the outer edge of the osseous spiral lamina, the fibers of the nerve pass
through the foramina in the tympanic lip; some end by arborizing around the bases of the inner hair cells, while others pass
between Corti’s rods and across the tunnel, to end in a similar manner in relation to the outer hair cells. The cochlear nerve
gives off a vestibular branch to supply the vestibular end of the ductus cochlearis; the filaments of this branch pass through
the foramina in the fossa cochlearis.
Vessels.—The arteries of the labyrinth are the internal auditory, from the basilar, and the stylomastoid, from the
posterior auricular. The internal auditory artery divides at the bottom of the internal acoustic meatus into two branches:
cochlear and vestibular. The cochlear branch subdivides into twelve or fourteen twigs, which traverse the canals in the modiolus, and are distributed, in the form of a capillary net-work, in the lamina spiralis and basilar membrane. The vestibular
branches are distributed to the utricle, saccule, and semicircular ducts.
The veins of the vestibule and semicircular canals accompany the arteries, and, receiving those of the cochlea at the
base of the modiolus, unite to form the internal auditory veins which end in the posterior part of the superior petrosal sinus
or in the transverse sinus.
Practice skills
Students are supposed to identify the following structures on the samples:
External ear
- carotid wall
- auricle
- membranous wall
- helix
- stapes
- antehelix
- incus
- tragus
- malleus
- antitragus
- auditory tube
- lobule of ear
Internal ear
- external acoustic meatus
- bony labyrinth
- tympanic membrane
- vestible
Middle ear
- semicircular canals
- tympanic cavity
- cochlea
- tegmental wall
- membranous labyrinth
- jugular wall
- labyrinthine wall
- mastoid wall
Self-taught class 5. The anatomy of the skin and its derivatives. The mammary gland. The conducting tracts of skin sensitivity.
The aim: to learn the general structure of skin and its derivates; to learn the structure and characteristics
of skin receptors; to find out the pathways of skin sensitivity; to learn the structure of the mammary gland.
Professional orientation: the knowledge of this topic is necessary for doctors of all the specialities; it
represents special interest for therapists, neurologists, neuropathologists, surgeons and others.
The plan of the self-taught class:
A. Learn the structure of common integument.
B. Learn the structure and characteristics of epidermis.
C. Learn the structure and characteristics of dermis.
D. Learn the development of common integument.
E. Learn the structure of the appendages of the skin – nails, hairs, sebaceous and sweat glands.
F. Learn the structure of the mammary gland, its development, nerve and vascular supply.
The common integument (integumentum commune; skin)
The integument covers the body and protects the deeper tissues from injury, from drying and from invasion by foreign organisms; it contains the peripheral endings of many of the sensory nerves; it plays an important part in the regulation
of the body temperature, and has also limited excretory and absorbing powers. It consists principally of a layer of vascular
connective tissue, named the corium or cutis vera, and an external covering of epithelium, termed the epidermis or cuticle. On the surface of the former layer are sensitive and vascular papillae within, or beneath it, are certain organs with
special functions: namely, the sudoriferous and sebaceous glands, and the hair follicles.
The epidermis, cuticle, or scarf skin is non-vascular, and consists of stratified epithelium, and is accurately moulded on the papillary layer of the corium. It varies in thickness in different parts. In some situations, as in the palms of the
hands and soles of the feet, it is thick, hard, and horny in texture. This may be in a measure due to the fact that these parts
are exposed to intermittent pressure, but that this is not the only cause is proved by the fact that the condition exists to a
very considerable extent at birth. The more superficial layers of cells, called the horny layer (stratum corneum), may be
separated by maceration from a deeper stratum, which is called the stratum mucosum, and which consists of several layers
of differently shaped cells. The free surface of the epidermis is marked by a net-work of linear furrows of variable size,
dividing the surface into a number of polygonal or lozenge-shaped areas. Some of these furrows are large, as opposite the
flexures of the joints, and correspond to the folds in the corium produced by movements. In other situations, as upon the
back of the hand, they are exceedingly fine, and intersect one another at various angles. Upon the palmar surfaces of the
hands and fingers, and upon the soles of the feet, the epidermal ridges are very distinct, and are disposed in curves; they
depend upon the large size and peculiar arrangements of the papillae upon which the epidermis is placed. The function of
these ridges is primarily to increase resistance between contact surfaces for the purpose of preventing slipping whether in
walking or prehension. The direction of the ridges is at right angles with the force that tends to produce slipping or to the
resultant of such forces when these forces vary in direction. In each individual the lines on the tips of the fingers and
thumbs form distinct patterns unlike those of any other person. A method of determining the identity of a criminal is based
on this fact, impressions (“finger-prints”) of these lines being made on paper covered with soot, or on white paper after first
covering the fingers with ink. The deep surface of the epidermis is accurately moulded upon the papillary layer of the corium, the papillae being covered by a basement membrane; so that when the epidermis is removed by maceration, it presents
on its under surface a number of pits or depressions corresponding to the papillae, and ridges corresponding to the intervals
between them. Fine tubular prolongations are continued from this layer into the ducts of the sudoriferous and sebaceous
glands.
The epidermis consists of stratified epithelium which is arranged in four layers from within outward as follows: (a)
stratum mucosum, (b) stratum granulosum, (c) stratum lucidum, and (d) stratum corneum.
The stratum mucosum (mucous layer) is composed of several layers of cells; those of the deepest layer are columnar in shape and placed perpendicularly on the surface of the basement membrane, to which they are attached by toothed
extremities; this deepest layer is sometimes termed the stratum germinativum; the succeeding strata consist of cells of a
more rounded or polyhedral form, the contents of which are soft, opaque, granular, and soluble in acetic acid. These are
known as prickle cells because of the bridges by which they are connected to one another. They contain fine fibrils which
are continuous across the connecting processes with corresponding fibrils in adjacent cells. Between the bridges are fine
inter-cellular clefts serving for the passage of lymph, and in these lymph corpuscles or pigment granules may be found.
The stratum granulosum comprises two or three layers of flattened cells which contain granules of eleidin, a substance readily stained by hematoxylin or carmine, and probably an intermediate substance in the formation of keratin. They
are supposed to be cells in a transitional stage between the protoplasmic cells of the stratum mucosum and the horny cells
of the superficial layers.
The stratum lucidum appears in section as a homogeneous or dimly striated membrane, composed of closely
packed cells in which traces of flattened nuclei may be found, and in which minute granules of a substance named keratohyalin are present.
The stratum corneum (horny layer) consists of several layers of horny epithelial scales in which no nuclei are discernible, and which are unaffected by acetic acid, the protoplasm having become changed into horny material or keratin.
According to Ranvier they contain granules of a material which has the characteristics of beeswax.
The black color of the skin in the negro, and the tawny color among some of the white races, is due to the presence
of pigment in the cells of the epidermis. This pigment is more especially distinct in the cells of the stratum mucosum, and is
similar to that found in the cells of the pigmentary layer of the retina. As the cells approach the surface and desiccate, the
color becomes partially lost; the disappearance of the pigment from the superficial layers of the epidermis is, however, difficult to explain.
The pigment (melanin) consists of dark brown or black granules of very small size, closely packed together within
the cells, but not involving the nucleus.
The main purpose served by the epidermis is that of protection, as the surface is worn away new cells are supplied
and thus the true skin, the vessels and nerves which it contains are defended from damage.
The Corium, Cutis Vera, Dermis, or True Skin is tough, flexible, and highly elastic. It varies in thickness in different parts of the body. Thus it is very thick in the palms of the hands and soles of the feet; thicker on the posterior aspect
of the body than on the front, and on the lateral than on the medial sides of the limbs. In the eyelids, scrotum, and penis it is
exceedingly thin and delicate.
It consists of felted connective tissue, with a varying amount of elastic fibers and numerous bloodvessels, lymphatics, and nerves. The connective tissue is arranged in two layers: a deeper or reticular, and a superficial or papillary. Unstriped muscular fibers are found in the superficial layers of the corium, wherever hairs are present, and in the subcutaneous
areolar tissue of the scrotum, penis, labia majora, and nipples. In the nipples the fibers are disposed in bands, closely reticulated and arranged in superimposed laminae.
The reticular layer (stratum reticulare; deep layer) consists of strong interlacing bands, composed chiefly of white
fibrous tissue, but containing some fibers of yellow elastic tissue, which vary in number in different parts; and connectivetissue corpuscles, which are often to be found flattened against the white fibrous tissue bundles. Toward the attached surface the fasciculi are large and coarse, and the areolae left by their interlacement are large, and occupied by adipose tissue
and sweat glands. Below the reticular layer is the subcutaneous areolar tissue, which, except in a few situations, contains
fat.
The papillary layer (stratum papillare; superficial layer; corpus papillare of the corium) consists of numerous
small, highly sensitive, and vascular eminences, the papillae, which rise perpendicularly from its surface. The papillae are
minute conical eminences, having rounded or blunted extremities, occasionally divided into two or more parts, and are received into corresponding pits on the under surface of the cuticle. On the general surface of the body, more especially in
parts endowed with slight sensibility, they are few in number, and exceedingly minute; but in some situations, as upon the
palmar surfaces of the hands and fingers, and upon the plantar surfaces of the feet and toes, they are long, of large size,
closely aggregated together, and arranged in parallel curved lines, forming the elevated ridges seen on the free surface of
the epidermis. Each ridge contains two rows of papillae, between which the ducts of the sudoriferous glands pass outward
to open on the summit of the ridge. Each papilla consists of very small and closely interlacing bundles of finely fibrillated
tissue, with a few elastic fibers; within this tissue is a capillary loop, and in some papillae, especially in the palms of the
hands and the fingers, there are tactile corpuscles.
Development.—The epidermis and its appendages, consisting of the hairs, nails, sebaceous and sweat glands, are
developed from the ectoderm, while the corium or true skin is of mesodermal origin. About the fifth week the epidermis
consists of two layers of cells, the deeper one corresponding to the rete mucosum. The subcutaneous fat appears about the
fourth month, and the papillae of the true skin about the sixth. A considerable desquamation of epidermis takes place during fetal life, and this desquamated epidermis, mixed with sebaceous secretion, constitutes the vernix caseosa, with which
the skin is smeared during the last three months of fetal life. The nails are formed at the third month, and begin to project
from the epidermis about the sixth. The hairs appear between the third and fourth months in the form of solid downgrowths
of the deeper layer of the epidermis, the growing extremities of which become inverted by papillary projections from the
corium. The central cells of the solid downgrowths undergo alteration to form the hair, while the peripheral cells are retained to form the lining cells of the hair-follicle. About the fifth month the fetal hairs (lanugo) appear, first on the head
and then on the other parts; they drop off after birth, and give place to the permanent hairs. The cellular structures of the
sudoriferous and sebaceous glands are formed from the ectoderm, while the connective tissue and bloodvessels are derived
from the mesoderm. All the sweat-glands are fully formed at birth; they begin to develop as early as the fourth month.
The arteries supplying the skin form a net-work in the subcutaneous tissue, and from this net-work branches are
given off to supply the sudoriferous glands, the hair follicles, and the fat. Other branches unite in a plexus immediately beneath the corium; from this plexus, fine capillary vessels pass into the papillae, forming, in the smaller ones, a single capillary loop, but in the larger, a more or less convoluted vessel. The lymphatic vessels of the skin form two net-works, superficial and deep, which communicate with each other and with those of the subcutaneous tissue by oblique branches.
The nerves of the skin terminate partly in the epidermis and partly in the corium; their different modes of ending are
described on pages 1059 to 1061.
The Appendages of the Skin—The appendages of the skin are the nails, the hairs, and the sudoriferous and sebaceous glands with their ducts.
The Nails (ungues) are flattened, elastic structures of a horny texture, placed upon the dorsal surfaces of the terminal
phalanges of the fingers and toes. Each nail is convex on its outer surface, concave within, and is implanted by a portion,
called the root, into a groove in the skin; the exposed portion is called the body, and the distal extremity the free edge. The
nail is firmly adherent to the corium, being accurately moulded upon its surface; the part beneath the body and root of the
nail is called the nail matrix, because from it the nail is produced. Under the greater part of the body of the nail, the matrix
is thick, and raised into a series of longitudinal ridges which are very vascular, and the color is seen through the transparent
tissue. Near the root of the nail, the papillae are smaller, less vascular, and have no regular arrangement, and here the tissue
of the nail is not firmly adherent to the connective-tissue stratum but only in contact with it; hence this portion is of a whiter color, and is called the lunula on account of its shape.
The cuticle as it passes forward on the dorsal surface of the finger or toe is attached to the surface of the nail a little
in advance of its root; at the extremity of the finger it is connected with the under surface of the nail a little behind its free
edge. The cuticle and the horny substance of the nail (both epidermic structures) are thus directly continuous with each other. The superficial, horny part of the nail consists of a greatly thickened stratum lucidum, the stratum corneum forming
merely the thin cuticular fold (eponychium) which overlaps the lunula; the deeper part consists of the stratum mucosum.
The cells in contact with the papillae of the matrix are columnar in form and arranged perpendicularly to the surface; those
which succeed them are of a rounded or polygonal form, the more superficial ones becoming broad, thin, and flattened, and
so closely packed as to make the limits of the cells very indistinct. The nails grow in length by the proliferation of the cells
of the stratum mucosum at the root of the nail, and in thickness from that part of the stratum mucosum which underlies the
lunula.
Hairs (pili) are found on nearly every part of the surface of the body, but are absent from the palms of the hands, the
soles of the feet, the dorsal surfaces of the terminal phalanges, the glans penis, the inner surface of the prepuce, and the
inner surfaces of the labia. They vary much in length, thickness, and color in different parts of the body and in different
races of mankind. In some parts, as in the skin of the eyelids, they are so short as not to project beyond the follicles containing them; in others, as upon the scalp, they are of considerable length; again, in other parts, as the eyelashes, the hairs of the
pubic region, and the whiskers and beard, they are remarkable for their thickness. Straight hairs are stronger than curly
hairs, and present on transverse section a cylindrical or oval outline; curly hairs, on the other hand, are flattened. A hair
consists of a root, the part implanted in the skin; and a shaft or scapus, the portion projecting from the surface.
The root of the hair (radix pili) ends in an enlargement, the hair bulb, which is whiter in color and softer in texture
than the shaft, and is lodged in a follicular involution of the epidermis called the hair follicle. When the hair is of considerable length the follicle extends into the subcutaneous cellular tissue. The hair follicle commences on the surface of the skin
with a funnel-shaped opening, and passes inward in an oblique or curved direction—the latter in curly hairs—to become
dilated at its deep extremity, where it corresponds with the hair bulb. Opening into the follicle, near its free extremity, are
the ducts of one or more sebaceous glands. At the bottom of each hair follicle is a small conical, vascular eminence or papilla, similar in every respect to those found upon the surface of the skin; it is continuous with the dermic layer of the follicle, and is supplied with nerve fibrils. The hair follicle consists of two coats—an outer or dermic, and an inner or epidermic.
The outer or dermic coat is formed mainly of fibrous tissue; it is continuous with the corium, is highly vascular,
and supplied by numerous minute nervous filaments. It consists of three layers. The most internal is a hyaline basement
membrane, which is well-marked in the larger hair follicles, but is not very distinct in the follicles of minute hairs; it is limited to the deeper part of the follicle. Outside this is a compact layer of fibers and spindle-shaped cells arranged circularly
around the follicle; this layer extends from the bottom of the follicle as high as the entrance of the ducts of the sebaceous
glands. Externally is a thick layer of connective tissue, arranged in longitudinal bundles, forming a more open texture and
corresponding to the reticular part of the corium; in this are contained the bloodvessels and nerves.
The inner or epidermic coat is closely adherent to the root of the hair, and consists of two strata named respectively
the outer and inner root sheaths; the former of these corresponds with the stratum mucosum of the epidermis, and resembles it in the rounded form and soft character of its cells; at the bottom of the hair follicle these cells become continuous
with those of the root of the hair. The inner root sheath consists of (1) a delicate cuticle next the hair, composed of a single
layer of imbricated scales with atrophied nuclei; (2) one or two layers of horny, flattened, nucleated cells, known as Huxley’s layer; and (3) a single layer of cubical cells with clear flattened nuclei, called Henle’s layer.
The hair bulb is moulded over the papilla and composed of polyhedral epithelial cells, which as they pass upward into the root of the hair become elongated and spindle-shaped, except some in the center which remain polyhedral. Some of
these latter cells contain pigment granules which give rise to the color of the hair. It occasionally happens that these pigment granules completely fill the cells in the center of the bulb; this gives rise to the dark tract of pigment often found, of
greater or less length, in the axis of the hair.
The shaft of the hair (scapus pili) consists, from within outward, of three parts, the medulla, the cortex, and the cuticle. The medulla is usually wanting in the fine hairs covering the surface of the body, and commonly in those of the head.
It is more opaque and deeper colored than the cortex when viewed by transmitted light; but when viewed by reflected light
it is white. It is composed of rows of polyhedral cells, containing granules of eleidin and frequently air spaces. The cortex
constitutes the chief part of the shaft; its cells are elongated and united to form flattened fusiform fibers which contain pigment granules in dark hair, and air in white hair. The cuticle consists of a single layer of flat scales which overlap one another from below upward.
Connected with the hair follicles are minute bundles of involuntary muscular fibers, termed the Arrectores pilorum. They arise from the superficial layer of the corium, and are inserted into the hair follicle, below the entrance of the
duct of the sebaceous gland. They are placed on the side toward which the hair slopes, and by their action diminish the
obliquity of the follicle and elevate the hair. The sebaceous gland is situated in the angle which the Arrector muscle forms
with the superficial portion of the hair follicle, and contraction of the muscle thus tends to squeeze the sebaceous secretion
out from the duct of the gland.
The Sebaceous Glands (glandulae sebaceae) are small, sacculated, glandular organs, lodged in the substance of the
corium. They are found in most parts of the skin, but are especially abundant in the scalp and face; they are also very numerous around the apertures of the anus, nose, mouth, and external ear, but are wanting in the palms of the hands and soles
of the feet. Each gland consists of a single duct, more or less capacious, which emerges from a cluster of oval or flaskshaped alveoli which vary from two to five in number, but in some instances there may be as many as twenty. Each alveo-
lus is composed of a transparent basement membrane, enclosing a number of epithelial cells. The outer or marginal cells
are small and polyhedral, and are continuous with the cells lining the duct. The remainder of the alveolus is filled with larger cells, containing fat, except in the center, where the cells have become broken up, leaving a cavity filled with their debris
and a mass of fatty matter, which constitutes the sebum cutaneum. The ducts open most frequently into the hair follicles,
but occasionally upon the general surface, as in the labia minora and the free margin of the lips. On the nose and face the
glands are of large size, distinctly lobulated, and often become much enlarged from the accumulation of pent-up secretion.
The tarsal glands of the eyelids are elongated sebaceous glands with numerous lateral diverticula.
The Sudoriferous or Sweat Glands (glandulae sudoriferae) are found in almost every part of the skin, and are situated in small pits on the under surface of the corium, or, more frequently, in the subcutaneous areolar tissue, surrounded by
a quantity of adipose tissue. Each consists of a single tube, the deep part of which is rolled into an oval or spherical ball,
named the body of the gland, while the superficial part, or duct, traverses the corium and cuticle and opens on the surface
of the skin by a funnel-shaped aperture. In the superficial layers of the corium the duct is straight, but in the deeper layers it
is convoluted or even twisted; where the epidermis is thick, as in the palms of the hands and soles of the feet, the part of the
duct which passes through it is spirally coiled. The size of the glands varies. They are especially large in those regions
where the amount of perspiration is great, as in the axillae, where they form a thin, mammillated layer of a reddish color,
which corresponds exactly to the situation of the hair in this region; they are large also in the groin. Their number varies.
They are very plentiful on the palms of the hands, and on the soles of the feet, where the orifices of the ducts are exceedingly regular, and open on the curved ridges; they are least numerous in the neck and back. On the palm there are about 370
per square centimeter; on the back of the hand about 200; forehead 175, breast, abdomen and forearm 155, and on the leg
and back from 60 to 80 per square centimeter. Krause estimates the total number at about 2,000,000. The average number
of sweat glands per square centimeter of skin area varies in different races.
They are absent in the deeper portion of the external auditory meatus, the prepuce and the glans penis. The tube,
both in the body of the gland and in the duct consists of two layers—an outer, of fine areolar tissue, and an inner of epithelium. The outer layer is thin and is continuous with the superficial stratum of the corium. In body of the gland the epithelium consists of a single layer of cubical cells, between the deep ends of which and the basement membrane is a layer of
longitudinally or obliquely arranged non-striped muscular fibers. The ducts are destitute of muscular fibers and are composed of a basement membrane lined by two or three layers of polyhedral cells; the lumen of the duct is coated by a thin
cuticle. When the cuticle is carefully removed from the surface of the corium, the ducts may be drawn out in the form of
short, thread-like processes on its under surface. The ceruminous glands of the external acoustic meatus and the ciliary
glands at the margins of the eyelids are modified sudoriferous glands.
Note. Professor Arthur Thomson, of Oxford, suggests that the contraction of these muscles on follicles which contain weak, flat hairs will tend to produce a permanent curve in the follicle, and this curve will be impressed on the hair
which is moulded within it, so that the hair, on emerging through the skin, will be curled. Curved hair follicles are characteristic of the scalp of the Bushman.
The mammae (mammary gland; breasts)
The mammae secrete the milk, and are accessory glands of the generative system. They exist in the male as well as
in the female; but in the former only in the rudimentary state, unless their growth is excited by peculiar circumstances. In
the female they are two large hemispherical eminences lying within the superficial fascia and situated on the front and sides
of the chest; each extends from the second rib above to the sixth rib below, and from the side of the sternum to near the
midaxillary line. Their weight and dimensions differ at different periods of life, and in different individuals. Before puberty
they are of small size, but enlarge as the generative organs become more completely developed. They increase during pregnancy and especially after delivery, and become atrophied in old age. The left mamma is generally a little larger than the
right. The deep surface of each is nearly circular, flattened, or slightly concave, and has its long diameter directed upward
and lateralward toward the axilla; it is separated from the fascia covering the Pectoralis major, Serratus anterior, and
Obliquus externus abdominis by loose connective tissue. The subcutaneous surface of the mamma is convex, and presents,
just below the center, a small conical prominence, the papilla.
The Mammary Papilla or Nipple (papilla mammae) is a cylindrical or conical eminence situated about the level of
the fourth intercostal space. It is capable of undergoing a sort of erection from mechanical excitement, a change mainly due
to the contraction of its muscular fibers. It is of a pink or brownish hue, its surface wrinkled and provided with secondary
papillae; and it is perforated by from fifteen to twenty orifices, the apertures of the lactiferous ducts. The base of the mammary papilla is surrounded by an areola. In the virgin the areola is of a delicate rosy hue; about the second month after impregnation it enlarges and acquires a darker tinge, and as pregnancy advances it may assume a dark brown or even black
color. This color diminishes as soon as lactation is over, but is never entirely lost throughout life. These changes in the color of the areola are of importance in forming a conclusion in a case of suspected first pregnancy. Near the base of the papilla, and upon the surface of the areola, are numerous large sebaceous glands, the areolar glands, which become much enlarged during lactation, and present the appearance of small tubercles beneath the skin. These glands secrete a peculiar fatty
substance, which serves as a protection to the integument of the papilla during the act of sucking. The mammary papilla
consists of numerous vessels, intermixed with plain muscular fibers, which are principally arranged in a circular manner
around the base: some few fibers radiating from base to apex.
Development.—The mamma is developed partly from mesoderm and partly from ectoderm—its bloodvessels and
connective tissue being derived from the former, its cellular elements from the latter. Its first rudiment is seen about the
third month, in the form of a number of small inward projections of the ectoderm, which invade the mesoderm; from these,
secondary tracts of cellular elements radiate and subsequently give rise to the epithelium of the glandular follicles and
ducts. The development of the follicles, however, remains imperfect, except in the parous female.
Structure.—The mamma consists of gland tissue; of fibrous tissue, connecting its lobes; and of fatty tissue in the
intervals between the lobes. The gland tissue, when freed from fibrous tissue and fat, is of a pale reddish color, firm in texture, flattened from before backward and thicker in the center than at the circumference. The subcutaneous surface of the
mamma presents numerous irregular processes which project toward the skin and are joined to it by bands of connective
tissue. It consists of numerous lobes, and these are composed of lobules, connected together by areolar tissue, bloodvessels,
and ducts. The smallest lobules consist of a cluster of rounded alveoli, which open into the smallest branches of the lactiferous ducts; these ducts unite to form larger ducts, and these end in a single canal, corresponding with one of the chief subdivisions of the gland. The number of excretory ducts varies from fifteen to twenty; they are termed the tubuli lactiferi.
They converge toward the areola, beneath which they form dilatations or ampullae, which serve as reservoirs for the milk,
and, at the base of the papillae, become contracted, and pursue a straight course to its summit, perforating it by separate
orifices considerably narrower than the ducts themselves. The ducts are composed of areolar tissue containing longitudinal
and transverse elastic fibers; muscular fibers are entirely absent; they are lined by columnar epithelium resting on a basement membrane. The epithelium of the mamma differs according to the state of activity of the organ. In the gland of a
woman who is not pregnant or suckling, the alveoli are very small and solid, being filled with a mass of granular polyhedral
cells. During pregnancy the alveoli enlarge, and the cells undergo rapid multiplication. At the commencement of lactation,
the cells in the center of the alveolus undergo fatty degeneration, and are eliminated in the first milk, as colostrum corpuscles. The peripheral cells of the alveolus remain, and form a single layer of granular, short columnar cells, with spherical
nuclei, lining the basement membrane. The cells, during the state of activity of the gland, are capable of forming, in their
interior, oil globules, which are then ejected into the lumen of the alveolus, and constitute the milk globules. When the acini
are distended by the accumulation of the secretion the lining epithelium becomes flattened.
The fibrous tissue invests the entire surface of the mamma, and sends down septa between its lobes, connecting
them together.
The fatty tissue covers the surface of the gland, and occupies the interval between its lobes. It usually exists in considerable abundance, and determines the form and size of the gland. There is no fat immediately beneath the areola and
papilla.
Vessels and Nerves.—The arteries supplying the mammae are derived from the thoracic branches of the axillary,
the intercostals, and the internal mammary. The veins describe an anastomotic circle around the base of the papilla, called
by Haller the circulus venosus. From this, large branches transmit the blood to the circumference of the gland, and end in
the axillary and internal mammary veins. The nerves are derived from the anterior and lateral cutaneous branches of the
fourth, fifth, and sixth thoracic nerves.
Practice skills
Students are supposed to identify the following structures on the samples:
Self-taught class 6. The conducting tracts of smell and taste.
The aim: to learn the pathways of smell and taste.
Professional orientation: the knowledge of this topic is necessary for doctors of all the specialities; it
represents special interest for therapists.
The plan of the self-taught class:
A. Revise the general principles of ascending conducting tract organization.
B. Learn the conducting tract of smell.
C. Learn the conducting tract of taste. Note that taste information is transmitted by three pairs of cranial
nerves.
Nerve fibers that stem from the olfactory bulb separate in the olfactory trigone: some run in the medial olfactory stria, others in the lateral olfactory stria. Some of the bulb fibers end in the olfactory trigone: the regions where the bulb fibers end
are known as the primary olfactory centers.
Medial Olfactory Stria
Its fibers end in the medial part of the anterior perforated substance, in the septum, in the paraterminal gyrus and in
that part of the hemisphere which lies lateral to it, the parolfactory (subcallosal) area. In those primary centers are relays
to numerous secondary tracts, of which the stria medullaris and the medial forebrain bundle are the most important. The
stria medullaris carries fibers from the parolfactory area and from the septum region to the habenular nuclei from which
the habenulotegmental tracts lead to the reticular formation of the brain stem. The medial anterior brain bundle, the medial
telencephalic fasciculus (fibrae otfacto-hypothalamo-tegmentales), connect the parolfactory area and the anterior perforated substance to the hypothalamic nuclei and the tegmentum of the midbrain.
The medial olfactory stria is supposed to be the essential pathway for the sense of smell. However, in animals anosmia
does not result from cutting only the lateral olfactory stria
Lateral Olfactory Stria
Its fibers end in the lateral part of the anterior perforated substance in the prepiriform cortex, the periamygdalold cortex
and the corticomedial part of the amygdaloid body.
Amygdaloid Body
The stria terminalis is the most important efferent fiber system of the amygdaloid body. It runs an arching course in the
marginal sulcus, between the caudate nucleus and the thalamus, as far as the anterior commissure. In doing this, it lies under the thalamostriate vein. Its fibers end in the septal nuclei, in the preoptic region and in nuclei of the hypothalamus.
Bundles of fibers pass from the stria terminalis over into the stria medullaris and then to the habenular ganglion. A large
number of other efferent bundles, particularly from the laterobasal part of the amygdaloid body, are together known as ventral amygdalofugai fibers. They pass inter alia to the entorhinal cortex, the hypothalamus and the medial thalamic nucleus, from which there are further connections to the frontal lobes. The stria terminalis contains many peptidergic fibers.
Rostral Commissure
The commissure joins the palaeocortical and the neocortical regions of the two hemispheres. Fibers of the olfactory tract
(anterior olfactory nucleus) and of the olfactory cortex cross to the opposite side in the anterior part. The anterior part is
poorly developed in man. The major section is formed by the posterior part where fibers of the temporal cortex mostly from
the cortex of the medial temporal gyrus, cross. In addition, the posterior part also receives crossed fibers from the amygdaloid body and the terminal stria.
In addition to the olfactory nerves two other paired nerves run from the nasal cavity to the brain, the terminal and vomeronasal nerves The terminal nerve consists of a bundle of fine fibers which extends from the wall of the nasal septum,
through the lamina cribrosa to the lamina terminalis and enters the brain below the anterior commissure The bundle includes numerous nerve cells and is regarded as a vegetative nerve The vomeronasal nerve, which extends from the vomeronasal organ to the accessory olfactory bulb is well developed in the lower vertebrates but is present in man only during
embryonic development. The vomeronasal organ (Jacobson’s organ) is a sensory epithelium in a pocket of mucous membrane on the wall of the nasal septum In reptiles it is said to be important for the detection of food.
The taste fibers are carried by three cranial nerves: the facial nerve (N. intermedius), the glossopharyngeal nerve and the
vagus nerve. The fibers arise from pseudounipolar neurons in the cranial nerve ganglia, the geniculate ganglion, the inferior
ganglion (petrosal) of the glossopharyngeal nerve and the inferior ganglion (nodose) of the vagus nerve. The taste fibers of
the facial nerve run via the chorda tympani to the lingual nerve and supply the receptors of the fungiform papillae on the
anterior two thirds of the tongue. The taste fibers of the glossopharyngeal nerve run in the lingual branches to the posterior
third of the tongue and supply the receptors of the vallate papillae. The taste fibers to the soft palate run in the tonsillar
branches. The taste fibers of the vagus nerve reach the epiglottis and the epipharynx through the pharyngeal branches.
The central processes of the neurons enter the medulla and form the tractus solitarius. They end in the nucleus of the tractus solitarius at about the level of the entry of the nerves. The nucleus enlarges In this region and contains a cell complex,
which is also known as the gustatory nucleus.
The secondary taste fibers arise from the nucleus of the tractus solitarius. Their pathway in the brain stem is not completely
known. It is assumed that the majority of fibers cross to the opposite side as arcuate fibers and join the medial lemniscus,
where they lie in its most medial part. Secondary taste fibers end in the medial part of the ventroposterior nucleus of the
thalamus. Tertiary fibers extend from there to a cortical region on the ventral surface of the parietal operculum, below the
postcentral region. The terminal zones in the thalamus and the cerebral cortex have been confirmed by experiments in
monkeys. Destruction of these regions in man, caused by disease, produces loss of taste perception in the contralateral half
of the tongue.
Some of the secondary fibers run to the hypothalamus. They are assumed to branch from the medial lemniscus in the midbrain and to pass through the mamillary peduncle to the mamillary body. Other fibers synapse in the ventral tegmental nucleus and are thought to reach the hypothalamus through the dorsal longitudinal fasciculus.
Collaterals pass from the neurons of the tractus solitarius to the salivatory nuclei. In this way they can produce reflex secretion of saliva as a response to taste sensations. Collaterals, which run to the dorsal nucleus of the vagus, form a reflex connection for gastric secretion due to taste stimulation.
Practice skills
Students are supposed to identify the following structures on the samples:
Self-taught class 7. The appendiculary apparatus of the eye.
The aim: to learn the components of the appendiculary apparatus of the eye; to learn the structure and functions of the accessory organs of the eye.
Professional orientation: the knowledge of this topic is necessary for doctors of all the specialities; it
represents special interest for ophthalmologists, therapists, and others.
The plan of the self-taught class:
A. Learn the origin, insertion and function of the ocular muscles.
B. Learn the structure and functions of the ocular fasciae.
C. Learn the structure and role of the eyebrows.
D. Learn the structure, function, nerve and blood supply of the eyelids.
E. Learn the structure and functions of the conjunctiva.
F. Learn the structures composing the lacrimal apparatus. Find out the way of eyewater production and
outflow.
The Accessory Organs of the Eye (Organa Oculi Accessoria)
The accessory organs of the eye include the ocular muscles, the fasciae, the eyebrows, the eyelids, the conjunctiva, and the lacrimal apparatus.
The Ocular Muscles (musculi oculi).—The ocular muscles are the:
Levator palpebrae superioris, Rectus medialis, Rectus superior, Rectus lateralis, Rectus inferior, Obliquus superior,
Obliquus inferior
The Levator palpebrae superioris is thin, flat, and triangular in shape. It arises from the under surface of the small
wing of the sphenoid, above and in front of the optic foramen, from which it is separated by the origin of the Rectus superior. At its origin, it is narrow and tendinous, but soon becomes broad and fleshy, and ends anteriorly in a wide aponeurosis
which splits into three lamellae. The superficial lamella blends with the upper part of the orbital septum, and is prolonged
forward above the superior tarsus to the palpebral part of the Orbicularis oculi, and to the deep surface of the skin of the
upper eyelid. The middle lamella, largely made up of non-striped muscular fibers, is inserted into the upper margin of the
superior tarsus, while the deepest lamella blends with an expansion from the sheath of the Rectus superior and with it is
attached to the superior fornix of the conjunctiva.
Whitnall has pointed out that the upper part of the sheath of the Levator palpebrae becomes thickened in front and
forms, above the anterior part of the muscle, a transverse ligamentous band which is attached to the sides of the orbital cavity. On the medial side it is mainly fixed to the pulley of the Obliquus superior, but some fibers are attached to the bone
behind the pulley and a slip passes forward and bridges over the supraorbital notch; on the lateral side it is fixed to the capsule of the lacrimal gland and to the frontal bone. In front of the transverse ligamentous band the sheath is continued over
the aponeurosis of the Levator palpebrae, as a thin connective-tissue layer which is fixed to the upper orbital margin immediatly behind the attachment of the orbital septum. When the Levator palpebrae contracts, the lateral and medial parts of the
ligamentous band are stretched and check the action of the muscle; the retraction of the upper eyelid is checked also by the
orbital septum coming into contact with the transverse part of the ligamentous band.
The four Recti arise from a fibrous ring (annulus tendineus communis) which surrounds the upper, medial, and lower margins of the optic foramen and encircles the optic nerve. The ring is completed by a tendinous bridge prolonged over
the lower and medial part of the superior orbital fissure and attached to a tubercle on the margin of the great wing of the
sphenoid, bounding the fissure. Two specialized parts of this fibrous ring may be made out: a lower, the ligament or tendon of Zinn, which gives origin to the Rectus inferior, part of the Rectus internus, and the lower head of origin of the Rectus lateralis; and an upper, which gives origin to the Rectus superior, the rest of the Rectus medialis, and the upper head of
the Rectus lateralis. This upper band is sometimes termed the superior tendon of Lockwood. Each muscle passes forward
in the position implied by its name, to be inserted by a tendinous expansion into the sclera, about 6 mm. from the margin of
the cornea. Between the two heads of the Rectus lateralis is a narrow interval, through which pass the two divisions of the
oculomotor nerve, the nasociliary nerve, the abducent nerve, and the ophthalmic vein. Although these muscles present a
common origin and are inserted in a similar manner into the sclera, there are certain differences to be observed in them as
regards their length and breadth. The Rectus medialis is the broadest, the Rectus lateralis the longest, and the Rectus superior the thinnest and narrowest.
The Obliquus oculi superior (superior oblique) is a fusiform muscle, placed at the upper and medial side of the orbit. It arises immediately above the margin of the optic foramen, above and medial to the origin of the Rectus superior, and,
passing forward, ends in a rounded tendon, which plays in a fibrocartilaginous ring or pulley attached to the trochlear fovea
of the frontal bone. The contiguous surfaces of the tendon and ring are lined by a delicate mucous sheath, and enclosed in a
thin fibrous investment. The tendon is reflected backward, lateralward, and downward beneath the Rectus superior to the
lateral part of the bulb of the eye, and is inserted into the sclera, behind the equator of the eyeball, the insertion of the muscle lying between the Rectus superior and Rectus lateralis.
The Obliquus oculi inferior (inferior oblique) is a thin, narrow muscle, placed near the anterior margin of the floor
of the orbit. It arises from the orbital surface of the maxilla, lateral to the lacrimal groove. Passing lateralward, backward,
and upward, at first between the Rectus inferior and the floor of the orbit, and then between the bulb of the eye and the Rectus lateralis, it is inserted into the lateral part of the sclera between the Rectus superior and Rectus lateralis, near to, but
somewhat behind the insertion of the Obliquus superior.
Nerves.—The Levator palpebrae superioris, Obliquus inferior, and the Recti superior, inferior, and medialis are
supplied by the oculomotor nerve; the Obliquus superior, by the trochlear nerve; the Rectus lateralis, by the abducent nerve.
Actions.—The Levator palpebrae raises the upper eyelid, and is the direct antagonist of the Orbicularis oculi. The
four Recti are attached to the bulb of the eye in such a manner that, acting singly, they will turn its corneal surface either
upward, downward, medialward, or lateralward, as expressed by their names. The movement produced by the Rectus superior or Rectus inferior is not quite a simple one, for inasmuch as each passes obliquely lateralward and forward to the bulb
of the eye, the elevation or depression of the cornea is accompanied by a certain deviation medialward, with a slight
amount of rotation. These latter movements are corrected by the Obliqui, the Obliquus inferior correcting the medial deviation caused by the Rectus superior and the Obliquus superior that caused by the Rectus inferior. The contraction of the Rectus lateralis or Rectus medialis, on the other hand, produces a purely horizontal movement. If any two neighboring Recti of
one eye act together they carry the globe of the eye in the diagonal of these directions, viz., upward and medialward, upward and lateralward, downward and medialward, or downward and lateralward. Sometimes the corresponding Recti of the
two eyes act in unison, and at other times the opposite Recti act together. Thus, in turning the eyes to the right, the Rectus
lateralis of the right eye will act in unison with the Rectus medialis of the left eye; but if both eyes are directed to an object
in the middle line at a short distance, the two Recti mediales will act in unison. The movement of circumduction, as in
looking around a room, is performed by the successive actions of the four Recti. The Obliqui rotate the eyeball on its antero-posterior axis, the superior directing the cornea downward and lateralward, and the inferior directing it upward and lat-
eralward; these movements are required for the correct viewing of an object when the head is moved laterally, as from
shoulder to shoulder, in order that the picture may fall in all respects on the same part of the retina of either eye.
A layer of non-striped muscle, the Orbitalis muscle of H. Müller, may be seen bridging across the inferior orbital
fissure.
The Fascia Bulb (capsule of Ténon) is a thin membrane which envelops the bulb of the eye from the optic nerve to
the ciliary region, separating it from the orbital fat and forming a socket in which it plays. Its inner surface is smooth, and is
separated from the outer surface of the sclera by the periscleral lymph space. This lymph space is continuous with the
subdural and subarachnoid cavities, and is traversed by delicate bands of connective tissue which extend between the fascia
and the sclera. The fascia is perforated behind by the ciliary vessels and nerves, and fuses with the sheath of the optic nerve
and with the sclera around the entrance of the optic nerve. In front it blends with the ocular conjunctiva, and with it is attached to the ciliary region of the eyeball. It is perforated by the tendons of the ocular muscles, and is reflected backward
on each as a tubular sheath. The sheath of the Obliquus superior is carried as far as the fibrous pulley of that muscle; that on
the Obliquus inferior reaches as far as the floor of the orbit, to which it gives off a slip. The sheaths on the Recti are gradually lost in the perimysium, but they give off important expansions. The expansion from the Rectus superior blends with the
tendon of the Levator palpebrae; that of the Rectus inferior is attached to the inferior tarsus. The expansions from the
sheaths of the Recti lateralis and medialis are strong, especially that from the latter muscle, and are attached to the lacrimal
and zygomatic bones respectively. As they probably check the actions of these two Recti they have been named the medial
and lateral check ligaments. Lockwood has described a thickening of the lower part of the facia bulbi, which he has
named the suspensory ligament of the eye. It is slung like a hammock below the eyeball, being expanded in the center,
and narrow at its extremities which are attached to the zygomatic and lacrimal bones respectively.
The Orbital Fascia forms the periosteum of the orbit. It is loosely connected to the bones and can be readily separated from them. Behind, it is united with the dura mater by processes which pass through the optic foramen and superior
orbital fissure, and with the sheath of the optic nerve. In front, it is connected with the periosteum at the margin of the orbit,
and sends off a process which assists in forming the orbital septum. From it two processes are given off; one to enclose the
lacrimal gland, the other to hold the pulley of the Obliquus superior in position.
The Eyebrows (supercilia) are two arched eminences of integument, which surmount the upper circumference of
the orbits, and support numerous short, thick hairs, directed obliquely on the surface. The eyebrows consist of thickened
integument, connected beneath with the Orbicularis oculi, Corrugator, and Frontalis muscles.
The Eyelids (palpebrae) are two thin, movable folds, placed in front of the eye, protecting it from injury by their
closure. The upper eyelid is the larger, and the more movable of the two, and is furnished with an elevator muscle, the Levator palpebrae superioris. When the eyelids are open, an elliptical space, the palpebral fissure (rima palpebrarum), is left
between their margins, the angles of which correspond to the junctions of the upper and lower eyelids, and are called the
palpebral commissures or canthi.
The lateral palpebral commissure (commissura palpebrarum lateralis; external canthus) is more acute than the
medial, and the eyelids here lie in close contact with the bulb of the eye: but the medial palpebral commissure (commissura palpebrarum medialis; internal canthus) is prolonged for a short distance toward the nose, and the two eyelids are
separated by a triangular space, the lacus lacrimalis. At the basal angles of the lacus lacrimalis, on the margin of each eyelid, is a small conical elevation, the lacrimal papilla, the apex of which is pierced by a small orifice, the punctum lacrimale, the commencement of the lacrimal duct.
The eyelashes (cilia) are attached to the free edges of the eyelids; they are short, thick, curved hairs, arranged in a
double or triple row: those of the upper eyelid, more numerous and longer than those of the lower, curve upward; those of
the lower eyelid curve downward, so that they do not interlace in closing the lids. Near the attachment of the eyelashes are
the openings of a number of glands, the ciliary glands, arranged in several rows close to the free margin of the lid; they are
regarded as enlarged and modified sudoriferous glands.
Structure of the Eyelids.—The eyelids are composed of the following structures taken in their order from without
inward: integument, areolar tissue, fibers of the Orbicularis oculi, tarsus, orbital septum, tarsal glands and conjunctiva. The
upper eyelid has, in addition, the aponeurosis of the Levator palpebrae superioris.
The integument is extremely thin, and continuous at the margins of the eyelids with the conjunctiva.
The subcutaneous areolar tissue is very lax and delicate, and seldom contains any fat.
The palpebral fibers of the Orbicularis oculi are thin, pale in color, and possess an involuntary action.
The tarsi (tarsal plates) are two thin, elongated plates of dense connective tissue, about 2.5 cm. in length; one is
placed in each eyelid, and contributes to its form and support. The superior tarsus (tarsus superior; superior tarsal plate),
the larger, is of a semilunar form, about 10 mm. in breadth at the center, and gradually narrowing toward its extremities. To
the anterior surface of this plate the aponeurosis of the Levator palpebrae superioris is attached. The inferior tarsus (tarsus
inferior; inferior tarsal plate), the smaller, is thin, elliptical in form, and has a vertical diameter of about 5 mm. The free or
ciliary margins of these plates are thick and straight. The attached or orbital margins are connected to the circumference of
the orbit by the orbital septum. The lateral angles are attached to the zygomatic bone by the lateral palpebral raphé. The
medial angles of the two plates end at the lacus lacrimalis, and are attached to the frontal process of the maxilla by the medial palpebral ligament.
The orbital septum (septum orbitale; palpebral ligament) is a membranous sheet, attached to the edge of the orbit,
where it is continuous with the periosteum. In the upper eyelid it blends by its peripheral circumference with the tendon of
the Levator palpebrae superioris and the superior tarsus, in the lower eyelid with the inferior tarsus. Medially it is thin, and,
becoming separated from the medial palpebral ligament, is fixed to the lacrimal bone immediately behind the lacrimal sac.
The septum is perforated by the vessels and nerves which pass from the orbital cavity to the face and scalp. The eyelids are
richly supplied with blood.
The Tarsal Glands (glandulae tarsales [Meibomi]; Meibomian glands).—The tarsal glands are situated upon the
inner surfaces of the eyelids, between the tarsi and conjunctiva, and may be distinctly seen through the latter on everting the
eyelids, presenting an appearance like parallel strings of pearls. There are about thirty in the upper eyelid, and somewhat
fewer in the lower. They are imbedded in grooves in the inner surfaces of the tarsi, and correspond in length with the
breadth of these plates; they are, consequently, longer in the upper than in the lower eyelid. Their ducts open on the free
magins of the lids by minute foramina.
Structure.—The tarsal glands are modified sebaceous glands, each consisting of a single straight tube or follicle,
with numerous small lateral diverticula. The tubes are supported by a basement membrane, and are lined at their mouths by
stratified epithelium; the deeper parts of the tubes and the lateral offshoots are lined by a layer of polyhedral cells.
The Conjunctiva is the mucous membrane of the eye. It lines the inner surfaces of the eyelids or palpebrae, and is
reflected over the forepart of the sclera and cornea.
The Palpebral Portion (tunica conjunctiva palpebrarum) is thick, opaque, highly vascular, and covered with numerous papillae, its deeper part presenting a considerable amount of lymphoid tissue. At the margins of the lids it becomes
continuous with the lining membrane of the ducts of the tarsal glands, and, through the lacrimal ducts, with the lining
membrane of the lacrimal sac and nasolacrimal duct. At the lateral angle of the upper eyelid the ducts of the lacrimal gland
open on its free surface; and at the medial angle it forms a semilunar fold, the plica semilunaris. The line of reflection of
the conjunctiva from the upper eyelid on to the bulb of the eye is named the superior fornix, and that from the lower lid
the inferior fornix.
The Bulbar Portion (tunica conjunctiva bulbi).—Upon the sclera the conjunctiva is loosely connected to the bulb
of the eye; it is thin, transparent, destitute of papillae, and only slightly vascular. Upon the cornea, the conjunctiva consists
only of epithelium, constituting the epithelium of the cornea, already described. Lymphatics arise in the conjunctiva in a
delicate zone around the cornea, and run to the ocular conjunctiva.
In and near the fornices, but more plentiful in the upper than in the lower eyelid, a number of convoluted tubular
glands open on the surface of the conjunctiva. Other glands, analogous to lymphoid follicles, and called by Henle trachoma glands, are found in the conjunctiva, and, according to Strohmeyer, are chiefly situated near the medial palpebral
commissure. They were first described by Brush, in his description of Peyer’s patches of the small intestine, as “identical
structures existing in the under eyelid of the ox.”
The caruncula lacrimalis is a small, reddish, conical-shaped body, situated at the medial palpebral commissure,
and filling up the lacus lacrimalis. It consists of a small island of skin containing sebaceous and sudoriferous glands, and is
the source of the whitish secretion which constantly collects in this region. A few slender hairs are attached to its surface.
Lateral to the caruncula is a slight semilunar fold of conjunctiva, the concavity of which is directed toward the cornea; it is
called the plica semilunaris. Müller found smooth muscular fibers in this fold; in some of the domesticated animals it contains a thin plate of cartilage.
The nerves in the conjunctiva are numerous and form rich plexuses. According to Krause they terminate in a peculiar form of tactile corpuscle, which he terms “terminal bulb.”
The Lacrimal Apparatus (apparatus lacrimalis) consists of (a) the lacrimal gland, which secretes the tears, and
its excretory ducts, which convey the fluid to the surface of the eye; (b) the lacrimal ducts, the lacrimal sac, and the nasolacrimal duct, by which the fluid is conveyed into the cavity of the nose.
The Lacrimal Gland (glandula lacrimalis).—The lacrimal gland is lodged in the lacrimal fossa, on the medial side
of the zygomatic process of the frontal bone. It is of an oval form, about the size and shape of an almond, and consists of
two portions, described as the superior and inferior lacrimal glands. The superior lacrimal gland is connected to the periosteum of the orbit by a few fibrous bands, and rests upon the tendons of the Recti superioris and lateralis, which separate it
from the bulb of the eye. The inferior lacrimal gland is separated from the superior by a fibrous septum, and projects into
the back part of the upper eyelid, where its deep surface is related to the conjunctiva. The ducts of the glands, from six to
twelve in number, run obliquely beneath the conjunctiva for a short distance, and open along the upper and lateral half of
the superior conjunctival fornix.
Structures of the Lacrimal Gland.—In structure and general appearance the lacrimal resembles the serous salivary
glands. In the recent state the cells are so crowded with granules that their limits can hardly be defined. They contain oval
nuclei, and the cell protoplasm is finely fibrillated.
The Lacrimal Ducts (ductus lacrimalis; lacrimal canals).—The lacrimal ducts, one in each eyelid, commence at
minute orifices, termed puncta lacrimalia, on the summits of the papillae lacrimales, seen on the margins of the lids at
the lateral extremity of the lacus lacrimalis. The superior duct, the smaller and shorter of the two, at first ascends, and then
bends at an acute angle, and passes medialward and downward to the lacrimal sac. The inferior duct at first descends, and
then runs almost horizontally to the lacrimal sac. At the angles they are dilated into ampullae; their walls are dense in
structure and their mucous lining is covered by stratified squamous epithelium, placed on a basement membrane. Outside
the latter is a layer of striped muscle, continuous with the lacrimal part of the Orbicularis oculi; at the base of each lacrimal
papilla the muscular fibers are circularly arranged and form a kind of sphincter.
The Lacrimal Sac (saccus lacrimalis).—The lacrimal sac is the upper dilated end of the nasolacrimal duct, and is
lodged in a deep groove formed by the lacrimal bone and frontal process of the maxilla. It is oval in form and measures
from 12 to 15 mm. in length; its upper end is closed and rounded; its lower is continued into the nasolacrimal duct. Its superficial surface is covered by a fibrous expansion derived from the medial palpebral ligament, and its deep surface is
crossed by the lacrimal part of the Orbicularis oculi, which is attached to the crest on the lacrimal bone.
Structure.—The lacrimal sac consists of a fibrous elastic coat, lined internally by mucous membrane: the latter is
continuous, through the lacrimal ducts, with the conjunctiva, and through the nasolacrimal duct with the mucous membrane
of the nasal cavity.
The Nasolacrimal Duct (ductus nasolacrimalis; nasal duct).—The nasolacrimal duct is a membranous canal, about
18 mm. in length, which extends from the lower part of the lacrimal sac to the inferior meatus of the nose, where it ends by
a somewhat expanded orifice, provided with an imperfect valve, the plica lacrimalis (Hasneri), formed by a fold of the
mucous membrane. It is contained in an osseous canal, formed by the maxilla, the lacrimal bone, and the inferior nasal concha; it is narrower in the middle than at either end, and is directed downward, backward, and a little lateralward. The mucous lining of the lacrimal sac and nasolacrimal duct is covered with columnar epithelium, which in places is ciliated.
Practice skills
Students are supposed to identify the following structures on the samples:
Accessory visual structures
- eyebrow
- extra-ocular muscles
- superior eyelid
- superior rectus
- inferior eyelid
- medial rectus
- conjunctiva
- lateral rectus
- superior fornix
- superior oblique
- inferior fornix
- inferior oblique
- lacrimal gland
Written tests of sensory organs
I. Questions for self-check
Most of the taste buds are located
_______________.
Chemicals (food) must be dissolved in saliva and
touch the _______________ for taste to occur.
____________ items are best detected by the back
of the tongue.
The olfactory bulb is located
_______________________.
Lacrimal secretion flows into the lacrimal sacs and
is deposited in the ____________.
The small, jerky movements of the eye are called
_________________.
The white, outer layer of the eye is the __________.
The nerve endings which register light are located
in the _____________.
The posterior chamber of the eye is filled with a
clear, gelatinous substance known as ______.
The clear outside layer in front of the eye is the
______________.
The ____________________________ focuses
light onto the retina.
The external ear, made of cartilage, is also known
as the _____________.
Sound travels through the ext. auditory canal and
directly strikes the _____________.
The ossicles (ear bones) are located in the
_________________.
Vibrations of cochlear fluid stimulate the
___________, which send nerve impulses to the
brain.
There are ___________ semicircular canals.
____________ results when something prevents
sound vibrations from getting to the inner ear.
The equilibrium receptors of the inner ear are called
the _________________.
Dynamic equilibrium is detected in the
_______________
II. Tests of basic theory
1. Which of the following muscles has no origin
from the common tendinous ring in the orbit?
A. medial rectus
B. *inferior oblique
C. levator palpebrae superioris
D. superior oblique
E. none of the above are correct
III. Tests from “Krok-1” database
1. A patient has a tumor in the superior nasal meatus region. Which function can be affected?
A. *Of smell.
B. Of salivation.
C. Of taste.
D. Of hearing.
E. Of swallowing.
2. A 35-year-old patient appealed to a doctor with
complains of severe coryza and olfaction loss
during a week. Examination of the nasal cavity
has shown a lot of mucus covering the mucous
3.
4.
5.
6.
7.
8.
tunic and blocking olfactory receptors. Name
the place of the nasal cavity where these receptors are located.
A. *Superior nasal concha.
B. Middle nasal concha.
C. Inferior nasal concha.
D. Common nasal meatus.
E. Vestibule of nose.
A 40-year-old man, who burnt an eyeball 2
weeks ago, was admitted to an ophthalmologic
department. Which of the listed eye structures
suffered?
A. Lens.
B. Ciliary body.
C. Iris.
D. *Cornea.
E. Vitreous body.
A 28-year-old patient got a factory chemical
burn of the face, a fluid got into the eye. The
consequence is the loss of sight. Which eyeball
structure was injured as a result of chemical
burn?
A.Vitreous body.
B. Lens.
C. *Cornea.
D.Retina.
E. Iris.
A patient has visual impairment: sectoranopia
of the medial field of vision on the right and the
lateral field of vision on the left. Which part of
the visual analyzer has pathological changes?
A.*Left optic tract.
B. Right optic tract.
C. Optic chiasm.
D.Right optic nerve.
E. Left optic nerve.
After an injury a patient got pupils' diameter
dilation and papillary reflex disorder. Which
muscle has been blocked?
A.Musculus ciliaris.
B. *Musculus sphincter pupillae.
C. Musculus dilatator pupillae.
D.Musculus rectus superior.
E. Musculus rectus inferior.
A 75-year-old patient is admitted to an oftalmological department with complaints of visual
impairment. Objectively there is an encephaloma in the site of the left visual tract. What disorders of vision will be observed?
A. *Sectoranopia in the left half of retina of
both eyes.
B. Sectoranopia in the right half of retina of
both eyes.
C. Sectoranopia in both halves of the left eye.
D. Sectoranopia in both halves of the right eye.
E. Sectoranopia in retina of both eyes.
A 25-year-old patient complained of the decreased vision. Accommodation disorders, di-
lated pupil, not reacting on the light were revealed on examination. Function of what muscles is disturbed?
A. Lateral rectus muscle, pupil narrowing
B. Pupil dilating muscle, ciliary
C. Pupil narrowing and dilating muscle
D. *Pupil narrowing muscle, ciliary
E. Inferior oblique muscle, ciliary
9. The increased intraocular tension is observed in
the patient with glaucoma. Secretion of aqueous
humor by the ciliar body is normal. Injury of
what structure of the eyeball wall caused the
disorder of flow-out from the anterior chamber?
A. *Venous sinus
B. Choroid
C. Ciliar body
D. Ciliary muscle
E. Back epithelium of cornea
10. The increased intraocular tension is observed in
the patient with glaucoma. Secretion of aqueous
humor by the ciliar body is normal. Injury of
what structure of the eyeball wall caused the
disorder of fluid flow-out from the anterior
chamber?
A. Back epithelium of cornea
B. *Venous sinus
C. Choroid
D. Ciliary muscle
E. Ciliar body
11. A 60-year-old patient has reduced perception of
high-frequency sounds. What structures' disorder of auditory analyzer caused these changes?
A. Main membrane of cochlea near the oval
window
B. Tympanic membrane
C. Muscles of middle ear
D. *Main membrane of cochlea near helicotrema
E. Eustachian tube
12. While shifting the gaze to the closely situated
object the refracting power of eye's optical mediums will increase by 10 diopters. It results
from changing of such eye structure:
A. Cornea
B. Muscle that dilatates pupil
C. *Lens
D. Vitreous body
E. Liquid of the anterior chamber of eye
UNIT 13. CRANIAL NERVES
Practice class 8. Written tests and examination of practice skills of sensory organs. Examination of self-taught tasks. Review of cranial nerves. I, II, ІІІ, ІV, VI, ХІ, ХІІ pairs of cranial
nerves.
The aim: to learn the origin, nuclei, course and objects of innervation of the I, II, ІІІ, ІV, VI, ХІ, ХІІ pairs
of cranial nerves.
Professional orientation: the knowledge of this topic is necessary for doctors of all specialities; it represents special interest for therapists.
The plan of the practice class:
A. Checking of the home assignment: oral quiz or written test control – 30 minutes.
B. Summary lecture on the topic by teacher – 30 minutes.
a) The origin and course of the I pair of cranial nerves.
b) The origin and course of the II pair of cranial nerves.
c) The nuclei, course and objects of innervation of the III pair of cranial nerves.
d) The nuclei, course and objects of innervation of the IV pair of cranial nerves.
e) The nuclei, course and objects of innervation of the VI pair of cranial nerves.
f) The nuclei, course and objects of innervation of the XI pair of cranial nerves.
g) The nuclei, course and objects of innervation of the XII pair of cranial nerves.
C. Students’ self-taught time – 55 minutes
D. Home-task – 5 minutes
I pair of cranial nerves - the Olfactory nerves (n. olfactorius)
The olfactory nerves or nerves of smell are distributed to the mucous membrane of the olfactory region of the nasal
cavity: this region comprises the superior nasal concha, and the corresponding part of the nasal septum. The nerves originate from the central or deep processes of the olfactory cells of the nasal mucous membrane. They form a plexiform network in the mucous membrane, and are then collected into about twenty branches, which pierce the cribriform plate of the
ethmoid bone in two groups, a lateral and a medial group, and end in the glomeruli of the olfactory bulb. Each branch
receives tubular sheaths from the dura mater and pia mater, the former being lost in the periosteum of the nose, the latter in
the neurolemma of the nerve.
The olfactory nerves are non-medullated, and consist of axis-cylinders surrounded by nucleated sheaths, in which,
however, there are fewer nuclei than are found in the sheaths of ordinary non-medullated nerve fibers.
The olfactory center in the cortex is generally associated with the rhinencephalon.
The olfactary nerves are developed from the cells of the ectoderm which lines the olfactory pits; these cells undergo
proliferation and give rise to what are termed the olfactory cells of the nose. The axons of the olfactory cells grow into the
overlying olfactory bulb and form the olfactory nerves.
II pair of cranial nerves - the Optic nerve (n. opticus)
The optic nerve, or nerve of sight, consists mainly of fibers derived from the ganglionic cells of the retina. These
axons terminate in arborizations around the cells in the lateral geniculate body, pulvinar, and superior colliculus which constitute the lower or primary visual centers. From the cells of the lateral geniculate body and the pulvinar fibers pass to the
cortical visual center, situated in the cuneus and in the neighborhood of the calcarine fissure. A few fibers of the optic
nerve, of small caliber, pass from the primary centers to the retina and are supposed to govern chemical changes in the retina and also the movements of some of its elements (pigment cells and cones). There are also a few fine fibers, afferent fibers, extending from the retina to the brain, that are supposed to be concerned in pupillary reflexes.
The optic nerve is peculiar in that its fibers and ganglion cells are probably third in the series of neurons from the receptors to the brain. Consequently the optic nerve corresponds rather to a tract of fibers within the brain than to the other
cranial nerves. Its fibers pass backward and medialward through the orbit and optic foramen to the optic commissure where
they partially decussate. The mixed fibers from the two nerves are continued in the optic tracts, the primary visual centers
of the brain.
The orbital portion of the optic nerve is from 20 mm. to 30 mm. in length and has a slightly sinuous course to allow
for movements of the eyeball. It is invested by an outer sheath of dura mater and an inner sheath from the arachnoid which
are attached to the sclera around the area where the nerve fibers pierce the choroid and sclera of the bulb. A little behind the
bulb of the eye the central artery of the retina with its accompanying vein perforates the optic nerve, and runs within it to
the retina. As the nerve enters the optic foramen its dural sheath becomes continuous with that lining the orbit and the optic
foramen. In the optic foramen the ophthalmic artery lies below and to its outer side. The intercranial portion of the optic
nerve is about 10 mm. in length.
The Optic Chiasma (chiasma opticum), somewhat quadrilateral in form, rests upon the tuberculum sellae and on the
anterior part of the diaphragma sellae. It is in relation, above, with the lamina terminalis; behind, with the tuber cinereum;
on either side, with the anterior perforated substance. Within the chiasma, the optic nerves undergo a partial decussation.
The fibers forming the medial part of each tract and posterior part of the chiasma have no connection with the optic nerves.
They simply cross in the chiasma, and connect the medial geniculate bodies of the two sides; they form the commissure of
Gudden. The remaining and principal part of the chiasma consists of two sets of fibers, crossed and uncrossed. The
crossed fibers which are the more numerous, occupy the central part of the chiasma, and pass from the optic nerve of one
side to the optic tract of the other, decussating in the chiasma with similar fibers of the opposite optic nerve. The uncrossed
fibers occupy the lateral part of the chiasma, and pass from the nerve of one side into the tract of the same side.
The crossed fibers of the optic nerve tend to occupy the medial side of the nerve and the uncrossed fibers the lateral
side. In the optic tract, however, the fibers are much more intermingled.
The Optic Tract passes backward and outward from the optic chiasma over the tuber cinereum and anterior perforated space to the cerebral peduncle and winds obliquely across its under surface. Its fibers terminate in the lateral geniculate body, the pulvinar and the superior colliculus. It is adherent to the tuber cinereum and the cerebral peduncle as it passes
over them. In the region of the lateral geniculate body it splits into two bands. The medial and smaller one is a part of the
commissure of Gudden and ends in the medial geniculate body.
From its mode of development, and from its structure, the optic nerve must be regarded as a prolongation of the
brain substance, rather than as an ordinary cerebrospinal nerve. As it passes from the brain it receives sheaths from the
three cerebral membranes, a perineural sheath from the pia mater, an intermediate sheath from the arachnoid, and an outer
sheath from the dura mater, which is also connected with the periosteum as it passes through the optic foramen. These
sheaths are separated from each other by cavities which communicate with the subdural and subarachnoid cavities respectively. The innermost or perineural sheath sends a process around the arteria centralis retinae into the interior of the nerve,
and enters intimately into its structure.
III pair of cranial nerves - the Oculomotor nerve (n. oculomotorius)
The oculomotor nerve supplies somatic motor fibers to all the ocular muscles, except the Obliquus superior and
Rectus lateralis; it also supplies through its connections with the ciliary ganglion, sympathetic motor fibers to the Sphincter
pupillae and the Ciliaris muscles.
The fibers of the oculomotor nerve arise from a nucleus which lies in the gray substance of the floor of the cerebral
aqueduct and extends in front of the aqueduct for a short distance into the floor of the third ventricle. From this nucleus the
fibers pass forward through the tegmentum, the red nucleus, and the medial part of the substantia nigra, forming a series of
curves with a lateral convexity, and emerge from the oculomotor sulcus on the medial side of the cerebral peduncle.
The nucleus of the oculomotor nerve does not consist of a continuous column of cells, but is broken up into a number of smaller nuclei, which are arranged in two groups, anterior and posterior. Those of the posterior group are six in number, five of which are symmetrical on the two sides of the middle line, while the sixth is centrally placed and is common to
the nerves of both sides. The anterior group consists of two nuclei, an antero-medial and an antero-lateral.
The nucleus of the oculomotor nerve, considered from a physiological standpoint, can be subdivided into several
smaller groups of cells, each group controlling a particular muscle.
On emerging from the brain, the nerve is invested with a sheath of pia mater, and enclosed in a prolongation from
the arachnoid. It passes between the superior cerebellar and posterior cerebral arteries, and then pierces the dura mater in
front of and lateral to the posterior clinoid process, passing between the free and attached borders of the tentorium cerebelli.
It runs along the lateral wall of the cavernous sinus, above the other orbital nerves, receiving in its course one or two filaments from the cavernous plexus of the sympathetic, and a communicating branch from the ophthalmic division of the trigeminal. It then divides into two branches, which enter the orbit through the superior orbital fissure, between the two heads
of the Rectus lateralis. Here the nerve is placed below the trochlear nerve and the frontal and lacrimal branches of the ophthalmic nerve, while the nasociliary nerve is placed between its two rami.
The superior ramus, the smaller, passes medialward over the optic nerve, and supplies the Rectus superior and Levator palpebrae superioris. The inferior ramus, the larger, divides into three branches. One passes beneath the optic nerve
to the Rectus medialis; another, to the Rectus inferior; the third and longest runs forward between the Recti inferior and
lateralis to the Obliquus inferior. From the last a short thick branch is given off to the lower part of the ciliary ganglion, and
forms its short root. All these branches enter the muscles on their ocular surfaces, with the exception of the nerve to the
Obliquus inferior, which enters the muscle at its posterior border.
IV pair of cranial nerves - the Trochlear nerve (n. trochlearis)
The trochlear nerve, the smallest of the cranial nerves, supplies the Obliquus superior oculi.
It arises from a nucleus situated in the floor of the cerebral aqueduct, opposite the upper part of the inferior colliculus. From its origin it runs downward through the tegmentum, and then turns backward into the upper part of the anterior
medullary velum. Here it decussates with its fellow of the opposite side and emerges from the surface of the velum at the
side of the frenulum veli, immediately behind the inferior colliculus.
The nerve is directed across the superior cerebellar peduncle, and then winds forward around the cerebral peduncle,
immediately above the pons, pierces the dura mater in the free border of the tentorium cerebelli, just behind, and lateral to,
the posterior clinoid process, and passes forward in the lateral wall of the cavernous sinus, between the oculomotor nerve
and the ophthalmic division of the trigeminal. It crosses the oculomotor nerve, and enters the orbit through the superior
orbital fissure. It now becomes the highest of all the nerves, and lies medial to the frontal nerve. In the orbit it passes medialward, above the origin of the Levator palpebrae superioris, and finally enters the orbital surface of the Obliquus superior.
In the lateral wall of the cavernous sinus the trochlear nerve forms communications with the ophthalmic division of
the trigeminal and with the cavernous plexus of the sympathetic. In the superior orbital fissure it occasionally gives off a
branch to the lacrimal nerve. It gives off a recurrent branch which passes backward between the layers of the tentorium
cerebelli and divides into two or three filaments which may be traced as far as the wall of the transverse sinus.
VI pair of cranial nerves - the Abducent nerve (n. abducens)
The abducent nerve supplies the Rectus lateralis oculi.
Its fibers arise from a small nucleus situated in the upper part of the rhomboid fossa, close to the middle line and beneath the colliculus facialis. They pass downward and forward through the pons, and emerge in the furrow between the
lower border of the pons and the upper end of the pyramid of the medulla oblongata.
From the nucleus of the sixth nerve, fibers are said to pass through the medial longitudinal fasciculus to the oculomotor nerve of the opposite side, along which they are carried to the Rectus medialis. The Rectus lateralis of one eye and
the Rectus medialis of the other may therefore be said to receive their nerves from the same nucleus.
The nerve pierces the dura mater on the dorsum sellae of the sphenoid, runs through a notch in the bone below the
posterior clinoid process, and passes forward through the cavernous sinus, on the lateral side of the internal carotid artery. It
enters the orbit through the superior orbital fissure, above the ophthalmic vein, from which it is separated by a lamina of
dura mater. It then passes between the two heads of the Rectus lateralis, and enters the ocular surface of that muscle. The
abducent nerve is joined by several filaments from the carotid and cavernous plexuses, and by one from the ophthalmic
nerve. The oculomotor, trochlear, ophthalmic, and abducent nerves bear certain relations to each other in the cavernous
sinus, at the superior orbital fissure, and in the cavity of the orbit, as follows:
In the cavernous sinus the oculomotor, trochlear, and ophthalmic nerves are placed in the lateral wall of the sinus,
in the order given, from above downward. The abducent nerve lies at the lateral side of the internal carotid artery. As these
nerves pass forward to the superior orbital fissure, the oculomotor and ophthalmic divide into branches and the abducent
nerve approaches the others; so that their relative positions are considerably changed.
In the superior orbital fissure the trochlear nerve and the frontal and lacrimal divisions of the ophthalmic lie in this
order from the medial to the lateral side upon the same plane; they enter the cavity of the orbit above the muscles. The remaining nerves enter the orbit between the two heads of the Rectus lateralis. The superior division of the oculomotor is the
highest of these; beneath this lies the nasociliary branch of the ophthalmic; then the inferior division of the oculomotor; and
the abducent lowest of all.
In the orbit, the trochlear, frontal, and lacrimal nerves lie immediately beneath the periosteum, the trochlear nerve
resting on the Obliquus superior, the frontal on the Levator palpebrae superioris, and the lacrimal on the Rectus lateralis.
The superior division of the oculomotor nerve lies immediately beneath the Rectus superior, while the nasociliary nerve
crosses the optic nerve to reach the medial wall of the orbit. Beneath these is the optic nerve, surrounded in front by the
ciliary nerves, and having the ciliary ganglion on its lateral side, between it and the Rectus lateralis. Below the optic nerve
are the inferior division of the oculomotor, and the abducent, the latter lying on the medial surface of the Rectus lateralis.
XI pair of cranial nerves - the Accessory nerve (n. accessorius; spinal accessory nerve)
The accessory nerve consists of two parts: a cranial and a spinal.
The Cranial Part (ramus internus; accessory portion) is the smaller of the two. Its fibers arise from the cells of the
nucleus ambiguus and emerge as four or five delicate rootlets from the side of the medulla oblongata, below the roots of
the vagus. It runs lateralward to the jugular foramen, where it interchanges fibers with the spinal portion or becomes united
to it for a short distance; here it is also connected by one or two filaments with the jugular ganglion of the vagus. It then
passes through the jugular foramen, separates from the spinal portion and is continued over the surface of the ganglion
nodosum of the vagus, to the surface of which it is adherent, and is distributed principally to the pharyngeal and superior
laryngeal branches of the vagus. Through the pharyngeal branch it probably supplies the Musculus uvulae and Levator veli
palatini. Some few filaments from it are continued into the trunk of the vagus below the ganglion, to be distributed with the
recurrent nerve and probably also with the cardiac nerves.
The Spinal Part (ramus externus; spinal portion) is firm in texture, and its fibers arise from the motor cells in the
lateral part of the anterior column of the gray substance of the medulla spinalis as low as the fifth cervical nerve. Passing
through the lateral funiculus of the medulla spinalis, they emerge on its surface and unite to form a single trunk, which ascends between the ligamentum denticulatum and the posterior roots of the spinal nerves; enters the skull through the foramen magnum, and is then directed to the jugular foramen, through which it passes, lying in the same sheath of dura mater
as the vagus, but separated from it by a fold of the arachnoid. In the jugular foramen, it receives one or two filaments from
the cranial part of the nerve, or else joins it for a short distance and then separates from it again. As its exit from the jugular
foramen, it runs backward in front of the internal jugular vein in 66.6 per cent. of cases, and behind in it 33.3 per cent. The
nerve then descends obliquely behind the Digastricus and Stylohyoideus to the upper part of the Sternocleidomastoideus; it
pierces this muscle, and courses obliquely across the posterior triangle of the neck, to end in the deep surface of the Trapezius. As it traverses the Sternocleidomastoideus it gives several filaments to the muscle, and joins with branches from the
second cervical nerve. In the posterior triangle it unites with the second and third cervical nerves, while beneath the Trapezius it forms a plexus with the third and fourth cervical nerves, and from this plexus fibers are distributed to the muscle.
XII pair of cranial nerves - the Hypoglossal nerve (n. hypoglossus)
The hypoglossal nerve is the motor nerve of the tongue.
Its fibers arise from the cells of the hypoglossal nucleus, which is an upward prolongation of the base of the anterior column of gray substance of the medulla spinalis. This nucleus is about 2 cm. in length, and its upper part corresponds
with the trigonum hypoglossi, or lower portion of the medial eminence of the rhomboid fossa. The lower part of the nucleus extends downward into the closed part of the medulla oblongata, and there lies in relation to the ventro-lateral aspect
of the central canal. The fibers run forward through the medulla oblongata, and emerge in the antero-lateral sulcus between
the pyramid and the olive.
The rootlets of this nerve are collected into two bundles, which perforate the dura mater separately, opposite the hypoglossal canal in the occipital bone, and unite together after their passage through it; in some cases the canal is divided
into two by a small bony spicule. The nerve descends almost vertically to a point corresponding with the angle of the mandible. It is at first deeply seated beneath the internal carotid artery and internal jugular vein, and intimately connected with
the vagus nerve; it then passes forward between the vein and artery, and lower down in the neck becomes superficial below
the Digastricus. The nerve then loops around the occipital artery, and crosses the external carotid and lingual arteries below
the tendon of the Digastricus. It passes beneath the tendon of the Digastricus, the Stylohyoideus, and the Mylohyoideus,
lying between the last-named muscle and the Hyoglossus, and communicates at the anterior border of the Hyoglossus with
the lingual nerve; it is then continued forward in the fibers of the Genioglossus as far as the tip of the tongue, distributing
branches to its muscular substance.
Branches of Communication.—Its branches of communication are, with the Vagus, First and second cervical
nerves, Sympathetic, Lingual.
The communications with the vagus take place close to the skull, numerous filaments passing between the hypoglossal and the ganglion nodosum of the vagus through the mass of connective tissue which unites the two nerves. As the nerve
winds around the occipital artery it gives off a filament to the pharyngeal plexus.
The communication with the sympathetic takes place opposite the atlas by branches derived from the superior cervical ganglion, and in the same situation the nerve is joined by a filament derived from the loop connecting the first and second cervical nerves.
The communications with the lingual take place near the anterior border of the Hyoglossus by numerous filaments
which ascend upon the muscle.
Branches of Distribution.—The branches of distribution of the hypoglossal nerve are: Meningeal, Thyrohyoid, Descending, Muscular.
Of these branches, the meningeal, descending, thyrohyoid, and the muscular twig to the Geniohyoideus, are probably
derived mainly from the branch which passes from the loop between the first and second cervical to join the hypoglossal.
Meningeal Branches (dural branches).—As the hypoglossal nerve passes through the hypoglossal canal it gives
off, according to Luschka, several filaments to the dura mater in the posterior fossa of the skull.
The Descending Ramus (ramus descendens; descendens hypoglossi), long and slender, quits the hypoglossal where
it turns around the occipital artery and descends in front of or in the sheath of the carotid vessels; it gives a branch to the
superior belly of the Omohyoideus, and then joins the communicantes cervicales from the second and third cervical nerves;
just below the middle of the neck, to form a loop, the ansa hypoglossi. From the convexity of this loop branches pass to
supply the Sternohyoideus, the Sternothyreoideus, and the inferior belly of the Omohyoideus. According to Arnold, another
filament descends in front of the vessels into the thorax, and joins the cardiac and phrenic nerves.
The Thyrohyoid Branch (ramus thyreohyoideus) arises from the hypoglossal near the posterior border of the hyoglossus; it runs obliquely across the greater cornu of the hyoid bone, and supplies the Thyreohyoideus muscle.
The Muscular Branches are distributed to the Styloglossus, Hyoglossus, Geniohyoideus, and Genioglossus. At the
under surface of the tongue numerous slender branches pass upward into the substance of the organ to supply its intrinsic
muscles.
Practice skills
Students are supposed to identify the following structures on the samples:
- optic nerve (II pair)
- abducent nerve (VI pair)
- oculomotor nerve (III pair)
- accessory nerve (XI pair)
- trochlear nerve (IV pair)
- hypoglossal nerve (ХП pair)
Practice class 9. V pair of cranial nerves: the trigeminal nerve. The innervation of skin of the
head.
The aim: to learn the trigeminal nerve, its branches and objects of innervation; to understand the innervation of the skin of the head.
Professional orientation: the knowledge of this topic is necessary for doctors of all specialities; it represents special interest for therapists, neurologists, neuropathologists and others.
The plan of the practice class:
A. Checking of the home assignment: oral quiz or written test control – 30 minutes.
B. Summary lecture on the topic by teacher – 30 minutes.
a) The general characteristic of nuclei, roots and ganglion of the trigeminal nerve.
b) The ophthalmic nerve and its branches.
c) The maxillary nerve and its branches.
d) The mandibular nerve and its branches.
C. Students’ self-taught time – 55 minutes
D. Home-task – 5 minutes
The Trigeminal Nerve (N. Trigeminus; Fifth Or Trifacial Nerve)
The trigeminal nerve is the largest cranial nerve and is the great sensory nerve of the head and face, and the motor
nerve of the muscles of mastication.
It emerges from the side of the pons, near its upper border, by a small motor and a large sensory root—the former
being situated in front of and medial to the latter.
Motor Root.—The fibers of the motor root arise from two nuclei, a superior and an inferior. The superior nucleus
consists of a strand of cells occupying the whole length of the lateral portion of the gray substance of the cerebral aqueduct.
The inferior or chief nucleus is situated in the upper part of the pons, close to its dorsal surface, and along the line of the
lateral margin of the rhomboid fossa. The fibers from the superior nucleus constitute the mesencephalic root: they descend
through the mid-brain, and, entering the pons, join with the fibers from the lower nucleus, and the motor root, thus formed,
passes forward through the pons to its point of emergence. It is uncertain whether the mesencephalic root is motor or sensory.
Sensory Root.—The fibers of the sensory root arise from the cells of the semilunar ganglion which lies in a cavity
of the dura mater near the apex of the petrous part of the temporal bone. They pass backward below the superior petrosal
sinus and tentorium cerebelli, and, entering the pons, divide into upper and lower roots. The upper root ends partly in a nucleus which is situated in the pons lateral to the lower motor nucleus, and partly in the locus caeruleus; the lower root descends through the pons and medulla oblongata, and ends in the upper part of the substantia gelatinosa of Rolando. This
lower root is sometimes named the spinal root of the nerve. Medullation of the fibers of the sensory root begins about the
fifth month of fetal life, but the whole of its fibers are not medullated until the third month after birth.
The Semilunar Ganglion (ganglion semilunare [Gasseri]; Gasserian ganglion) occupies a cavity (cavum Meckelii)
in the dura mater covering the trigeminal impression near the apex of the petrous part of the temporal bone. It is somewhat
crescentic in shape, with its convexity directed forward: medially, it is in relation with the internal carotid artery and the
posterior part of the cavernous sinus. The motor root runs in front of and medial to the sensory root, and passes beneath the
ganglion; it leaves the skull through the foramen ovale, and, immediately below this foramen, joins the mandibular nerve.
The greater superficial petrosal nerve lies also underneath the ganglion.
The ganglion receives, on its medial side, filaments from the carotid plexus of the sympathetic. It gives off minute
branches to the tentorium cerebelli, and to the dura mater in the middle fossa of the cranium. From its convex border, which
is directed forward and lateralward, three large nerves proceed, viz., the ophthalmic, maxillary, and mandibular. The
ophthalmic and maxillary consist exclusively of sensory fibers; the mandibular is joined outside the cranium by the motor
root.
Associated with the three divisions of the trigeminal nerve are four small ganglia. The ciliary ganglion is connected
with the ophthalmic nerve; the sphenopalatine ganglion with the maxillary nerve; and the otic and submaxillary ganglia
with the mandibular nerve. All four receive sensory filaments from the trigeminal, and motor and sympathetic filaments
from various sources; these filaments are called the roots of the ganglia.
The Ophthalmic Nerve (n. ophthalmicus), or first division of the trigeminal, is a sensory nerve. It supplies branches to the cornea, ciliary body, and iris; to the lacrimal gland and conjunctiva; to the part of the mucous membrane of the
nasal cavity; and to the skin of the eyelids, eyebrow, forehead, and nose. It is the smallest of the three divisions of the trigeminal, and arises from the upper part of the semilunar ganglion as a short, flattened band, about 2.5 cm. long, which
passes forward along the lateral wall of the cavernous sinus, below the oculomotor and trochlear nerves; just before entering the orbit, through the superior orbital fissure, it divides into three branches, lacrimal, frontal, and nasociliary.
The ophthalmic nerve is joined by filaments from the cavernous plexus of the sympathetic, and communicates with
the oculomotor, trochlear, and abducent nerves; it gives off a recurrent filament which passes between the layers of the tentorium.
The Lacrimal Nerve (n. lacrimalis) is the smallest of the three branches of the ophthalmic. It sometimes receives a
filament from the trochlear nerve, but this is possibly derived from the branch which goes from the ophthalmic to the trochlear nerve. It passes forward in a separate tube of dura mater, and enters the orbit through the narrowest part of the superior
orbital fissure. In the orbit it runs along the upper border of the Rectus lateralis, with the lacrimal artery, and communicates
with the zygomatic branch of the maxillary nerve. It enters the lacrimal gland and gives off several filaments, which supply
the gland and the conjunctiva. Finally it pierces the orbital septum, and ends in the skin of the upper eyelid, joining with
filaments of the facial nerve. The lacrimal nerve is occasionally absent, and its place is then taken by the zygomaticotemporal branch of the maxillary. Sometimes the latter branch is absent, and a continuation of the lacrimal is substituted for it.
The Frontal Nerve (n. frontalis) is the largest branch of the ophthalmic, and may be regarded, both from its size and
direction, as the continuation of the nerve. It enters the orbit through the superior orbital fissure, and runs forward between
the Levator palpebrae superioris and the periosteum. Midway between the apex and base of the orbit it divides into two
branches, supratrochlear and supraorbital.
The supratrochlear nerve (n. supratrochlearis), the smaller of the two, passes above the pulley of the Obliquus superior, and gives off a descending filament, to join the infratrochlear branch of the nasociliary nerve. It then escapes from
the orbit between the pulley of the Obliquus superior and the supraorbital foramen, curves up on to the forehead close to the
bone, ascends beneath the Corrugator and Frontalis, and dividing into branches which pierce these muscles, it supplies the
skin of the lower part of the forehead close to the middle line and sends filaments to the conjunctiva and skin of the upper
eyelid.
The supraorbital nerve (n. supraorbitalis) passes through the supraorbital foramen, and gives off, in this situation,
palpebral filaments to the upper eyelid. It then ascends upon the forehead, and ends in two branches, a medial and a lateral,
which supply the integument of the scalp, reaching nearly as far back as the lambdoidal suture; they are at first situated
beneath the Frontalis, the medial branch perforating the muscle, the lateral branch the galea aponeurotica. Both branches
supply small twigs to the pericranium.
The Nasociliary Nerve (n. nasociliaris; nasal nerve) is intermediate in size between the frontal and lacrimal, and is
more deeply placed. It enters the orbit between the two heads of the Rectus lateralis, and between the superior and inferior
rami of the oculomotor nerve. It passes across the optic nerve and runs obliquely beneath the Rectus superior and Obliquus
superior, to the medial wall of the orbital cavity. Here it passes through the anterior ethmoidal foramen, and, entering the
cavity of the cranium, traverses a shallow groove on the lateral margin of the front part of the cribriform plate of the ethmoid bone, and runs down, through a slit at the side of the crista galli, into the nasal cavity. It supplies internal nasal
branches to the mucous membrane of the front part of the septum and lateral wall of the nasal cavity. Finally, it emerges,
as the external nasal branch, between the lower border of the nasal bone and the lateral nasal cartilage, and, passing down
beneath the Nasalis muscle, supplies the skin of the ala and apex of the nose.
The nasociliary nerve gives off the following branches, viz.: the long root of the ciliary ganglion, the long ciliary,
and the ethmoidal nerves.
The long root of the ciliary ganglion (radix longa ganglii ciliaris) usually arises from the nasociliary between the
two heads of the Rectus lateralis. It passes forward on the lateral side of the optic nerve, and enters the postero-superior
angle of the ciliary ganglion; it is sometimes joined by a filament from the cavernous plexus of the sympathetic, or from the
superior ramus of the trochlear nerve.
The long ciliary nerves (nn. ciliares longi), two or three in number, are given off from the nasociliary, as it crosses
the optic nerve. They accompany the short ciliary nerves from the ciliary ganglion, pierce the posterior part of the sclera,
and running forward between it and the choroid, are distributed to the iris and cornea. The long ciliary nerves are supposed
to contain sympathetic fibers from the superior cervical ganglion to the Dilator pupillae muscle.
The infratrochlear nerve (n. infratrochlearis) is given off from the nasociliary just before it enters the anterior
ethmoidal foramen. It runs forward along the upper border of the Rectus medialis, and is joined, near the pulley of the
Obliquus superior, by a filament from the supratrochlear nerve. It then passes to the medial angle of the eye, and supplies
the skin of the eyelids and side of the nose, the conjunctiva, lacrimal sac, and caruncula lacrimalis.
The ethmoidal branches (nn. ethmoidales) supply the ethmoidal cells; the posterior branch leaves the orbital cavity
through the posterior ethmoidal foramen and gives some filaments to the sphenoidal sinus.
The Ciliary Ganglion (ophthalmic or lenticular ganglion).—The ciliary ganglion is a small, sympathetic ganglion,
of a reddish-gray color, and about the size of a pin’s head; it is situated at the back part of the orbit, in some loose fat between the optic nerve and the Rectus lateralis muscle, lying generally on the lateral side of the ophthalmic artery.
Its roots are three in number, and enter its posterior border. One, the long or sensory root, is derived from the nasociliary nerve, and joins its postero-superior angle. The second, the short or motor root, is a thick nerve (occasionally divided into two parts) derived from the branch of the oculomotor nerve to the Obliquus inferior, and connected with the postero-inferior angle of the ganglion. The motor root is supposed to contain sympathetic efferent fibers (preganglionic fibers)
from the nucleus of the third nerve in the mid-brain to the ciliary ganglion where they form synapses with neurons whose
fibers (postganglionic) pass to the Ciliary muscle and to Sphincter muscle of the pupil. The third, the sympathetic root, is a
slender filament from the cavernous plexus of the sympathetic; it is frequently blended with the long root. According to
Tiedemann, the ciliary ganglion receives a twig of communication from the sphenopalatine ganglion.
Its branches are the short ciliary nerves. These are delicate filaments, from six to ten in number, which arise from
the forepart of the ganglion in two bundles connected with its superior and inferior angles; the lower bundle is the larger.
They run forward with the ciliary arteries in a wavy course, one set above and the other below the optic nerve, and are accompanied by the long ciliary nerves from the nasociliary. They pierce the sclera at the back part of the bulb of the eye,
pass forward in delicate grooves on the inner surface of the sclera, and are distributed to the Ciliaris muscle, iris, and cornea. Tiedemann has described a small branch as penetrating the optic nerve with the arteria centralis retinae.
The Maxillary Nerve (n. maxillaris; superior maxillary nerve), or second division of the trigeminal, is a sensory
nerve. It is intermediate, both in position and size, between the ophthalmic and mandibular. It begins at the middle of the
semilunar ganglion as a flattened plexiform band, and, passing horizontally forward, it leaves the skull through the foramen
rotundum, where it becomes more cylindrical in form, and firmer in texture. It then crosses the pterygopalatine fossa, inclines lateralward on the back of the maxilla, and enters the orbit through the inferior orbital fissure; it traverses the infraorbital groove and canal in the floor of the orbit, and appears upon the face at the infraorbital foramen. At its termination,
the nerve lies beneath the Quadratus labii superioris, and divides into a leash of branches which spread out upon the side of
the nose, the lower eyelid, and the upper lip, joining with filaments of the facial nerve.
Branches.—Its branches may be divided into four groups, according as they are given off in the cranium, in the
pterygopalatine fossa, in the infraorbital canal, or on the face.
In the Cranium – Middle meningeal.
In the Pterygopalatine Fossa – Zygomatic, Sphenopalatine, Posterior superior alveolar.
In the Infraorbital Canal – Anterior superior alveolar, Middle superior alveolar.
On the Face – Inferior palpebral, External nasal, Superior labial.
The Middle Meningeal Nerve (n. meningeus medius; meningeal or dural branch) is given off from the maxillary
nerve directly after its origin from the semilunar ganglion; it accompanies the middle meningeal artery and supplies the
dura mater.
The Zygomatic Nerve (n. zygomaticus; temporomalar nerve; orbital nerve) arises in the pterygopalatine fossa, enters the orbit by the inferior orbital fissure, and divides at the back of that cavity into two branches, zygomaticotemporal
and zygomaticofacial.
The zygomaticotemporal branch (ramus zygomaticotemporalis; temporal branch) runs along the lateral wall of
the orbit in a groove in the zygomatic bone, receives a branch of communication from the lacrimal, and, passing through a
foramen in the zygomatic bone, enters the temporal fossa. It ascends between the bone, and substance of the Temporalis
muscle, pierces the temporal fascia about 2.5 cm. above the zygomatic arch, and is distributed to the skin of the side of the
forehead, and communicates with the facial nerve and with the aurićulotemporal branch of the mandibular nerve.
As it pierces the temporal fascia, it gives off a slender twig, which runs between the two layers of the fascia to the lateral
angle of the orbit.
The zygomaticofacial branch (ramus zygomaticofacialis; malar branch) passes along the infero-lateral angle of the
orbit, emerges upon the face through a foramen in the zygomatic bone, and, perforating the Orbicularis oculi, supplies the
skin on the prominence of the cheek. It joins with the facial nerve and with the inferior palpebral branches of the maxillary.
The Sphenopalatine Branches (nn. sphenopalatini), two in number, descend to the sphenopalatine ganglion.
The Posterior Superior Alveolar Branches (rami alveolares superiores posteriores; posterior superior dental
branches) arise from the trunk of the nerve just before it enters the infraorbital groove; they are generally two in number,
but sometimes arise by a single trunk. They descend on the tuberosity of the maxilla and give off several twigs to the gums
and neighboring parts of the mucous membrane of the cheek. They then enter the posterior alveolar canals on the infratemporal surface of the maxilla, and, passing from behind forward in the substance of the bone, communicate with the middle
superior alveolar nerve, and give off branches to the lining membrane of the maxillary sinus and three twigs to each molar
tooth; these twigs enter the foramina at the apices of the roots of the teeth.
The Middle Superior Alveolar Branch (ramus alveolaris superior medius; middle superior dental branch), is given off from the nerve in the posterior part of the infraorbital canal, and runs downward and forward in a canal in the lateral
wall of the maxillary sinus to supply the two premolar teeth. It forms a superior dental plexus with the anterior and posterior superior alveolar branches.
The Anterior Superior Alveolar Branch (ramus alveolaris superior anteriores; anterior superior dental branch),
of considerable size, is given off from the nerve just before its exit from the infraorbital foramen; it descends in a canal in
the anterior wall of the maxillary sinus, and divides into branches which supply the incisor and canine teeth. It communicates with the middle superior alveolar branch, and gives off a nasal branch, which passes through a minute canal in the
lateral wall of the inferior meatus, and supplies the mucous membrane of the anterior part of the inferior meatus and the
floor of the nasal cavity, communicating with the nasal branches from the sphenopalatine ganglion.
The Inferior Palpebral Branches (rami palpebrales inferiores; palpebral branches) ascend behind the Orbicularis
oculi. They supply the skin and conjunctiva of the lower eyelid, joining at the lateral angle of the orbit with the facial and
zygomaticofacial nerves.
The External Nasal Branches (rami nasales externi) supply the skin of the side of the nose and of the septum mobile nasi, and join with the terminal twigs of the nasociliary nerve.
The Superior Labial Branches (rami labiales superiores; labial branches), the largest and most numerous, descend behind the Quadratus labii superioris, and are distributed to the skin of the upper lip, the mucous membrane of the
mouth, and labial glands. They are joined, immediately beneath the orbit, by filaments from the facial nerve, forming with
them the infraorbital plexus.
Sphenopalatine Ganglion (ganglion of Meckel).—The sphenopalatine ganglion, the largest of the sympathetic
ganglia associated with the branches of the trigeminal nerve, is deeply placed in the pterygopalatine fossa, close to the
sphenopalatine foramen. It is triangular or heart-shaped, of a reddish-gray color, and is situated just below the maxillary
nerve as it crosses the fossa. It receives a sensory, a motor, and a sympathetic root.
Its sensory root is derived from two sphenopalatine branches of the maxillary nerve; their fibers, for the most part,
pass directly into the palatine nerves; a few, however, enter the ganglion, constituting its sensory root. Its motor root is
probably derived from the nervus intermedius through the greater superficial petrosal nerve and is supposed to consist in
part of sympathetic efferent (preganglionic) fibers from the medulla. In the sphenopalatine ganglion they form synapses
with neurons whose postganglionic axons, vasodilator and secretory fibers, are distributed with the deep branches of the
trigeminal to the mucous membrane of the nose, soft palate, tonsils, uvula, roof of the mouth, upper lip and gums, and to
the upper part of the pharynx. Its sympathetic root is derived from the carotid plexus through the deep petrosal nerve.
These two nerves join to form the nerve of the pterygoid canal before their entrance into the ganglion.
The greater superficial petrosal nerve (n. petrosus superficialis major; large superficial petrosal nerve) is given
off from the genicular ganglion of the facial nerve; it passes through the hiatus of the facial canal, enters the cranial cavity,
and runs forward beneath the dura mater in a groove on the anterior surface of the petrous portion of the temporal bone. It
then enters the cartilaginous substance which fills the foramen lacerum, and joining with the deep petrosal branch forms the
nerve of the pterygoid canal.
The deep petrosal nerve (n. petrosus profundus; large deep petrosal nerve) is given off from the carotid plexus,
and runs through the carotid canal lateral to the internal carotid artery. It then enters the cartilaginous substance which fills
the foramen lacerum, and joins with the greater superficial petrosal nerve to form the nerve of the pterygoid canal.
The nerve of the pterygoid canal (n. canalis pterygoidei [Vidii]; Vidian nerve), formed by the junction of the two
preceding nerves in the cartilaginous substance which fills the foramen lacerum, passes forward, through the pterygoid canal, with the corresponding artery, and is joined by a small ascending sphenoidal branch from the otic ganglion. Finally, it
enters the pterygopalatine fossa, and joins the posterior angle of the sphenopalatine ganglion.
Branches of Distribution.—These are divisible into four groups, viz., orbital, palatine, posterior superior nasal,
and pharyngeal.
The orbital branches (rami orbitales; ascending branches) are two or three delicate filaments, which enter the orbit
by the inferior orbital fissure, and supply the periosteum. According to Luschka, some filaments pass through foramina in
the frontoethmoidal suture to supply the mucous membrane of the posterior ethmoidal and sphenoidal sinuses.
The palatine nerves (nn. palatini; descending branches) are distributed to the roof of the mouth, soft palate, tonsil,
and lining membrane of the nasal cavity. Most of their fibers are derived from the sphenopalatine branches of the maxillary
nerve. They are three in number: anterior, middle, and posterior.
The anterior palatine nerve (n. palatinus anterior) descends through the pterygopalatine canal, emerges upon the
hard palate through the greater palatine foramen, and passes forward in a groove in the hard palate, nearly as far as the incisor teeth. It supplies the gums, the mucous membrane and glands of the hard palate, and communicates in front with the
terminal filaments of the nasopalatine nerve. While in the pterygopalatine canal, it gives off posterior inferior nasal
branches, which enter the nasal cavity through openings in the palatine bone, and ramify over the inferior nasal concha and
middle and inferior meatuses; at its exit from the canal, a palatine branch is distributed to both surfaces of the soft palate.
The middle palatine nerve (n. palatinus medius) emerges through one of the minor palatine canals and distributes
branches to the uvula, tonsil, and soft palate. It is occasionally wanting.
The posterior palatine nerve (n. palatinus posterior) descends through the pterygopalatine canal, and emerges by a
separate opening behind the greater palatine foramen; it supplies the soft palate, tonsil, and uvula. The middle and posterior
palatine join with the tonsillar branches of the glossopharyngeal to form a plexus (circulus tonsillaris) around the tonsil.
The posterior superior nasal branches (rami nasales posteriores superiores) are distributed to the septum and lateral wall of the nasal fossa. They enter the posterior part of the nasal cavity by the sphenopalatine foramen and supply the
mucous membrane covering the superior and middle nasal conchae, the lining of the posterior ethmoidal cells, and the posterior part of the septum. One branch, longer and larger than the others, is named the nasopalatine nerve. It enters the nasal cavity through the sphenopalatine foramen, passes across the roof of the nasal cavity below the orifice of the sphenoidal
sinus to reach the septum, and then runs obliquely downward and forward between the periosteum and mucous membrane
of the lower part of the septum. It descends to the roof of the mouth through the incisive canal and communicates with the
corresponding nerve of the opposite side and with the anterior palatine nerve. It furnishes a few filaments to the mucous
membrane of the nasal septum.
The pharyngeal nerve (pterygopalatine nerve) is a small branch arising from the posterior part of the ganglion. It passes
through the pharyngeal canal with the pharyngeal branch of the internal maxillary artery, and is distributed to the mucous
membrane of the nasal part of the pharynx, behind the auditory tube.
The mandibular nerve (n. mandibularis; inferior maxillary nerve) supplies the teeth and gums of the mandible, the
skin of the temporal region, the auricula, the lower lip, the lower part of the face, and the muscles of mastication; it also
supplies the mucous membrane of the anterior two-thirds of the tongue. It is the largest of the three divisions of the fifth,
and is made up of two roots: a large, sensory root proceeding from the inferior angle of the semilunar ganglion, and a
small motor root (the motor part of the trigeminal), which passes beneath the ganglion, and unites with the sensory root,
just after its exit through the foramen ovale. Immediately beneath the base of the skull, the nerve gives off from its medial
side a recurrent branch (nervus spinosus) and the nerve to the Pterygoideus internus, and then divides into two trunks, an
anterior and a posterior.
The Nervus Spinosus (recurrent or meningeal branch) enters the skull through the foramen spinosum with the
middle meningeal artery. It divides into two branches, anterior and posterior, which accompany the main divisions of the
artery and supply the dura mater; the posterior branch also supplies the mucous lining of the mastoid cells; the anterior
communicates with the meningeal branch of the maxillary nerve.
The Internal Pterygoid Nerve (n. pterygoideus internus).—The nerve to the Pterygoideus internus is a slender
branch, which enters the deep surface of the muscle; it gives off one or two filaments to the otic ganglion.
The anterior and smaller division of the mandibular nerve receives nearly the whole of the fibers of the motor root of
the nerve, and supplies the muscles of mastication and the skin and mucous membrane of the cheek. Its branches are the
masseteric, deep temporal, buccinator, and external pterygoid.
The Masseteric Nerve (n. massetericus) passes lateralward, above the Pterygoideus externus, in front of the temporomandibular articulation, and behind the tendon of the Temporalis; it crosses the mandibular notch with the masseteric
artery, to the deep surface of the Masseter, in which it ramifies nearly as far as its anterior border. It gives a filament to the
temporomandibular joint.
The Deep Temporal Nerves (nn. temporales profundi) are two in number, anterior and posterior. They pass above
the upper border of the Pterygoideus externus and enter the deep surface of the Temporalis. The posterior branch, of small
size, is placed at the back of the temporal fossa, and sometimes arises in common with the masseteric nerve. The anterior
branch is frequently given off from the buccinator nerve, and then turns upward over the upper head of the Pterygoideus
externus. Frequently a third or intermediate branch is present.
The Buccinator Nerve (n. buccinatorus; long buccal nerve) passes forward between the two heads of the Pterygoideus externus, and downward beneath or through the lower part of the Temporalis; it emerges from under the anterior
border of the Masseter, ramifies on the surface of the Buccinator, and unites with the buccal branches of the facial nerve. It
supplies a branch to the Pterygoideus externus during its passage through that muscle, and may give off the anterior deep
temporal nerve. The buccinator nerve supplies the skin over the Buccinator, and the mucous membrane lining its inner surface.
External Pterygoid Nerve (n. pterygoideus externus).—The nerve to the Pterygoideus externus frequently arises
in conjunction with the buccinator nerve, but it may be given off separately from the anterior division of the mandibular
nerve. It enters the deep surface of the muscle.
The posterior and larger division of the mandibular nerve is for the most part sensory, but receives a few filaments
from the motor root. It divides into auriculotemporal, lingual, and inferior alveolar nerves.
The Auriculotemporal Nerve (n. auriculotemporalis) generally arises by two roots, between which the middle meningeal artery ascends. It runs backward beneath the Pterygoideus externus to the medial side of the neck of the mandible.
It then turns upward with the superficial temporal artery, between the auricula and condyle of the mandible, under cover of
the parotid gland; escaping from beneath the gland, it ascends over the zygomatic arch, and divides into superficial temporal branches.
The branches of communication of the auriculotemporal nerve are with the facial nerve and with the otic ganglion.
The branches to the facial, usually two in number, pass forward from behind the neck of the mandible and join the facial
nerve at the posterior border of the Masseter. The filaments to the otic ganglion are derived from the roots of the auriculotemporal nerve close to their origin.
Its branches of distribution are:
Anterior auricular, Articular, Branches to the external acoustic meatus, Parotid, Superficial temporal.
The anterior auricular branches (nn. auriculares anteriores) are usually two in number; they supply the front of
the upper part of the auricula, being distributed principally to the skin covering the front of the helix and tragus.
The branches to the external acoustic meatus (n. meatus auditorii externi), two in number, enter the meatus between its bony and cartilaginous portions and supply the skin lining it; the upper one sends a filament to the tympanic
membrane.
The articular branches consist of one or two twigs which enter the posterior part of the temporomandibular joint.
The parotid branches (rami parotidei) supply the parotid gland.
The superficial temporal branches (rami temporales superficiales) accompany the superficial temporal artery to
the vertex of the skull; they supply the skin of the temporal region and communicate with the facial and zygomaticotemporal nerves.
The Lingual Nerve (n. lingualis) supplies the mucous membrane of the anterior two-thirds of the tongue. It lies at
first beneath the Pterygoideus externus, medial to and in front of the inferior alveolar nerve, and is occasionally joined to
this nerve by a branch which may cross the internal maxillary artery. The chorda tympani also joins it at an acute angle in
this situation. The nerve then passes between the Pterygoideus internus and the ramus of the mandible, and crosses obliquely to the side of the tongue over the Constrictor pharyngis superior and Styloglossus, and then between the Hyoglossus and
deep part of the submaxillary gland; it finally runs across the duct of the submaxillary gland, and along the tongue to its tip,
lying immediately beneath the mucous membrane.
Its branches of communication are with the facial (through the chorda tympani), the inferior alveolar and hypoglossal nerves, and the submaxillary ganglion. The branches to the submaxillary ganglion are two or three in number; those
connected with the hypoglossal nerve form a plexus at the anterior margin of the Hyoglossus.
Its branches of distribution supply the sublingual gland, the mucous membrane of the mouth, the gums, and the
mucous membrane of the anterior two-thirds of the tongue; the terminal filaments communicate, at the tip of the tongue,
with the hypoglossal nerve.
The Inferior Alveolar Nerve (n. alveolaris inferior; inferior dental nerve) is the largest branch of the mandibular
nerve. It descends with the inferior alveolar artery, at first beneath the Pterygoideus externus, and then between the sphenomandibular ligament and the ramus of the mandible to the mandibular foramen. It then passes forward in the mandibular
canal, beneath the teeth, as far as the mental foramen, where it divides into two terminal branches, incisive and mental.
The branches of the inferior alveolar nerve are the mylohyoid, dental, incisive, and mental.
The mylohyoid nerve (n. mylohyoideus) is derived from the inferior alveolar just before it enters the mandibular foramen. It descends in a groove on the deep surface of the ramus of the mandible, and reaching the under surface of the
Mylohyoideus supplies this muscle and the anterior belly of the Digastricus.
The dental branches supply the molar and premolar teeth. They correspond in number to the roots of those teeth;
each nerve entering the orifice at the point of the root, and supplying the pulp of the tooth; above the alveolar nerve they
form an inferior dental plexus.
The incisive branch is continued onward within the bone, and supplies the canine and incisor teeth.
The mental nerve (n. mentalis) emerges at the mental foramen, and divides beneath the Triangularis muscle into
three branches; one descends to the skin of the chin, and two ascend to the skin and mucous membrane of the lower lip;
these branches communicate freely with the facial nerve.
Two small ganglia, the otic and the submaxillary, are connected with the mandibular nerve.
Otic Ganglion (ganglion oticum).—The otic ganglion is a small, ovalshaped, flattened ganglion of a reddish-gray
color, situated immediately below the foramen ovale; it lies on the medial surface of the mandibular nerve, and surrounds
the origin of the nerve to the Pterygoideus internus. It is in relation, laterally, with the trunk of the mandibular nerve at the
point where the motor and sensory roots join; medially, with the cartilaginous part of the auditory tube, and the origin of the
Tensor veli palatini; posteriorly, with the middle meningeal artery.
Branches of Communication.—It is connected by two or three short filaments with the nerve to the Pterygoideus
internus, from which it may obtain a motor, and possibly a sensory root. It communicates with the glossopharyngeal and
facial nerves, through the lesser superficial petrosal nerve continued from the tympanic plexus, and through this nerve it
probably receives a root from the glossopharyngeal and a motor root from the facial; its sympathetic root consists of a filament from the plexus surrounding the middle meningeal artery. The fibers from the glossopharyngeal which pass to the otic
ganglion in the small superficial petrosal are supposed to be sympathetic efferent (preganglionic) fibers from the dorsal
nucleus or inferior salivatory nucleus of the medulla. Fibers (postganglionic) from the otic ganglion with which these form
synapses are supposed to pass with the auriculotemporal nerve to the parotid gland. A slender filament (sphenoidal) ascends from it to the nerve of the Pterygoid canal, and a small branch connects it with the chorda tympani.
Its branches of distribution are: a filament to the Tensor tympani, and one to the Tensor veli palatini. The former
passes backward, lateral to the auditory tube; the latter arises from the ganglion, near the origin of the nerve to the Pterygoideus internus, and is directed forward. The fibers of these nerves are, however, mainly derived from the nerve to the
Pterygoideus internus.
Submaxillary Ganglion (ganglion submaxillare).—The submaxillary ganglion is of small size and is fusiform in
shape. It is situated above the deep portion of the submaxillary gland, on the hyoglossus, near the posterior border of the
Mylohyoideus, and is connected by filaments with the lower border of the lingual nerve. It is suspended from the lingual
nerve by two filaments which join the anterior and posterior parts of the ganglion. Through the posterior of these it receives
a branch from the chorda tympani nerve which runs in the sheath of the lingual; these are sympathetic efferent (preganglionic) fibers from the facial nucleus or the superior salivatory nucleus of the medulla oblongata that terminate in the submaxillary ganglion. The postganglionic fibers pass to the submaxillary gland, it communicates with the sympathetic by
filaments from the sympathetic plexus around the external maxillary artery.
Its branches of distribution are five or six in number; they arise from the lower part of the ganglion, and supply
the mucous membrane of the mouth and the duct of the submaxillary gland, some being lost in the submaxillary gland. The
branch of communication from the lingual to the forepart of the ganglion is by some regarded as a branch of distribution,
through which filaments pass from the ganglion to the lingual nerve, and by it are conveyed to the sublingual gland and the
tongue.
Trigeminal Nerve Reflexes.—Pains referred to various branches of the trigeminal nerve are of very frequent occurrence, and should always lead to a careful examination in order to discover a local cause. As a general rule the diffusion of
pain over the various branches of the nerve is at first confined to one only of the main divisions, and the search for the
causative lesion should always commence with a thorough examination of all those parts which are supplied by that division; although in severe cases pain may radiate over the branches of the other main divisions. The commonest example of
this condition is the neuralgia which is so often associated with dental caries—here, although the tooth itself may not appear to be painful, the most distressing referred pains may be experienced, and these are at once relieved by treatment directed to the affected tooth.
Many other examples of trigeminal reflexes could be quoted, but it will be sufficient to mention the more common
ones. Dealing with the ophthalmic nerve, severe supraorbital pain is commonly associated with acute glaucoma or with
disease of the frontal or ethmoidal air cells. Malignant growths or empyema of the maxillary antrum, or unhealthy conditions about the inferior conchae or the septum of the nose, are often found giving rise to “second division” neuralgia, and
should be always looked for in the absence of dental disease in the maxilla.
It is on the mandibular nerve, however, that some of the most striking reflexes are seen. It is quite common to meet
with patients who complain of pain in the ear, in whom there is no sign of aural disease, and the cause is usually to be
found in a carious tooth in the mandible. Moreover, with an ulcer or cancer of the tongue, often the first pain to be experienced is one which radiates to the ear and temporal fossa, over the distribution of the auriculotemporal nerve.
Note. After it enters the infraorbital canal, the nerve is frequently called the infraorbital.
Practice skills
Students are supposed to identify the following structures on the samples:
Trigeminal nerve (V pair) and its ganglion
- auriculotemporal nerve
- ophthalmic nerve (1 branch of V pair)
- lingual nerve
- maxillary nerve (2 branch of V pair)
- inferior alveolar nerve
- mandibular nerve (3 branch of V pair)
Practice class 10. The facial nerve (VIІ). The glossopharyngeal (ІХ) nerve.
The aim: to learn the facial and glossopharyngeal nerves, their branches and objects of innervation.
Professional orientation: the knowledge of this topic is necessary for doctors of all specialities; it represents special interest for therapists, neurologists, neuropathologists and others.
The plan of the practice class:
A. Checking of the home assignment: oral quiz or written test control – 30 minutes.
B. Summary lecture on the topic by teacher – 30 minutes.
a) The general characteristic if the facial nerve, its nuclei; roots and ganglion.
b) The branches of communication of the facial nerve.
c) The branches of distribution of the facial nerve.
d) The glossopharyngeal nerve.
C. Students’ self-taught time – 55 minutes
D. Home-task – 5 minutes
The Facial Nerve (N. Facialis; Seventh Nerve)
The facial nerve consists of a motor and a sensory part, the latter being frequently described under the name of the
nervus intermedius (pars intermedii of Wrisberg). The two parts emerge at the lower border of the pons in the recess between the olive and the inferior peduncle, the motor part being the more medial, immediately to the lateral side of the sensory part is the acoustic nerve.
The motor part supplies somatic motor fibers to the muscles of the face, scalp, and auricle, the Buccinator and Platysma, the Stapedius, the Stylohyoideus, and posterior belly of the Digastricus; it also contains some sympathetic motor
fibers which constitute the vasodilator nerves of the submaxillary and sublingual glands, and are conveyed through the
chorda tympani nerve. These are preganglionic fibers of the sympathetic system and terminate in the submaxillary ganglion
and small ganglia in the hilus of the submaxillary gland. From these ganglia postganglionic fibers are conveyed to these
glands. The sensory part contains the fibers of taste for the anterior two-thirds of the tongue and a few somatic sensory fibers from the middle ear region. A few splanchnic sensory fibers are also present.
The motor root arises from a nucleus which lies deeply in the reticular formation of the lower part of the pons. This
nucleus is situated above the nucleus ambiguus, behind the superior olivary nucleus, and medial to the spinal tract of the
trigeminal nerve. From this origin the fibers pursue a curved course in the substance of the pons. They first pass backward
and medialward toward the rhomboid fossa, and, reaching the posterior end of the nucleus of the abducent nerve, run upward close to the middle line beneath the colliculus fasciculus. At the anterior end of the nucleus of the abducent nerve they
make a second bend, and run downward and forward through the pons to their point of emergence between the olive and
the inferior peduncle.
The sensory root arises from the genicular ganglion, which is situated on the geniculum of the facial nerve in the
facial canal, behind the hiatus of the canal. The cells of this ganglion are unipolar, and the single process divides in a Tshaped manner into central and peripheral branches. The central branches leave the trunk of the facial nerve in the internal
acoustic meatus, and form the sensory root; the peripheral branches are continued into the chorda tympani and greater superficial petrosal nerves. Entering the brain at the lower border of the pons between the motor root and the acoustic nerve,
the fibers of the sensory root pass into the substance of the medulla oblongata and end in the upper part of the terminal nucleus of the glossopharyngeal nerve and in the fasciculus solitarius
From their superficial attachments to the brain, the two roots of the facial nerve pass lateralward and forward with
the acoustic nerve to the internal acoustic meatus. In the meatus the motor root lies in a groove on the upper and anterior
surface of the acoustic nerve, the sensory root being placed between them.
At the bottom of the meatus, the facial nerve enters the facial canal, which it traverses to its termination at the stylomastoid foramen. It is at first directed lateralward between the cochlea and vestibule toward the medial wall of the tympanic cavity; it then bends suddenly backward and arches downward behind the tympanic cavity to the stylomastoid foramen. The point where it changes its direction is named the geniculum; it presents a reddish gangliform swelling, the genicular ganglion (ganglion geniculi; geniculate ganglion; nucleus of the sensory root of the nerve). On emerging from the
stylomastoid foramen, the facial nerve runs forward in the substance of the parotid gland, crosses the external carotid artery, and divides behind the ramus of the mandible into branches, from which numerous offsets are distributed over the side
of the head, face, and upper part of the neck, supplying the superficial muscles in these regions. The branches and their
offsets unite to form the parotid plexus.
Branches of Communication.—The branches of communication of the facial nerve may be arranged as follows:
In the internal acoustic meatus - with the acoustic nerve; at the genicular ganglion; with the sphenopalatine ganglion
by the greater superficial petrosal nerve; with the otic ganglion by a branch which joins the lesser superficial petrosal nerve;
with the sympathetic on the middle meningeal artery.
In the facial canal - with the auricular branch of the vagus; at its exit from the stylomastoid foramen; with the glossopharyngeal; with the vagus; with the great auricular; with the auriculotemporal.
Behind the ear - with the lesser occipital.
On the face - with the trigeminal.
In the neck - with the cutaneous cervical.
In the internal acoustic meatus some minute filaments pass from the facial to the acoustic nerve.
The greater superficial petrosal nerve (large superficial petrosal nerve) arises from the genicular ganglion, and
consists chiefly of sensory branches which are distributed to the mucous membrane of the soft palate; but it probably contains a few motor fibers which form the motor root of the sphenopalatine ganglion. It passes forward through the hiatus of
the facial canal, and runs in a sulcus on the anterior surface of the petrous portion of the temporal bone beneath the semilunar ganglion, to the foramen lacerum. It receives a twig from the tympanic plexus, and in the foramen is joined by the deep
petrosal, from the sympathetic plexus on the internal carotid artery, to form the nerve of the pterygoid canal which passes
forward through the pterygoid canal and ends in the sphenopalatine ganglion. The genicular ganglion is connected with the
otic ganglion by a branch which joins the lesser superficial petrosal nerve, and also with the sympathetic filaments accompanying the middle meningeal artery. According to Arnold, a twig passes back from the ganglion to the acoustic nerve. Just
before the facial nerve emerges from the stylomastoid foramen, it generally receives a twig from the auricular branch of the
vagus.
After its exit from the stylomastoid foramen, the facial nerve sends a twig to the glossopharyngeal, and communicates with the auricular branch of the vagus, with the great auricular nerve of the cervical plexus, with the auriculotemporal
nerve in the parotid gland, and with the lesser occipital behind the ear; on the face with the terminal branches of the trigeminal, and in the neck with the cutaneous cervical nerve.
Branches of Distribution.—The branches of distribution of the facial nerve may be thus arranged:
With the facial canal - nerve to the Stapedius muscle; chorda tympani.
At its exit from the stylomastoid foramen - Posterior auricular; Digastric; Stylohyoid.
On the face – Temporal; Zygomatic; Buccal ; Mandibular; Cervical.
The Nerve to the Stapedius (n. stapedius; tympanic branch) arises opposite the pyramidal eminence; it passes
through a small canal in this eminence to reach the muscle.
The Chorda Tympani Nerve is given off from the facial as it passes downward behind the tympanic cavity, about 6
mm. from the stylomastoid foramen. It runs upward and forward in a canal, and enters the tympanic cavity, through an aperture (iter chordae posterius) on its posterior wall, close to the medial surface of the posterior border of the tympanic
membrane and on a level with the upper end of the manubrium of the malleus. It traverses the tympanic cavity, between the
fibrous and mucous layers of the tympanic membrane, crosses the manubrium of the malleus, and emerges from the cavity
through a foramen situated at the inner end of the petrotympanic fissure, and named the iter chordae anterius (canal of
Huguier). It then descends between the Pterygoideus externus and internus on the medial surface of the spina angularis of
the sphenoid, which it sometimes grooves, and joins, at an acute angle, the posterior border of the lingual nerve. It receives
a few efferent fibers from the motor root; these enter the submaxillary ganglion, and through it are distributed to the submaxillary and sublingual glands; the majority of its fibers are afferent, and are continued onward through the muscular substance of the tongue to the mucous membrane covering its anterior two-thirds; they constitute the nerve of taste for this
portion of the tongue. Before uniting with the lingual nerve the chorda tympani is joined by a small branch from the otic
ganglion.
The Posterior Auricular Nerve (n. auricularis posterior) arises close to the stylo-mastoid foramen, and runs upward in front of the mastoid process; here it is joined by a filament from the auricular branch of the vagus, and communicates with the posterior branch of the great auricular, and with the lesser occipital. As it ascends between the external
acoustic meatus and mastoid process it divides into auricular and occipital branches. The auricular branch supplies the
Auricularis posterior and the intrinsic muscles on the cranial surface of the auricula. The occipital branch, the larger, passes backward along the superior nuchal line of the occipital bone, and supplies the Occipitalis.
The Digastric Branch (ramus digastricus) arises close to the stylomastoid foramen, and divides into several filaments, which supply the posterior belly of the Digastricus; one of these filaments joins the glossopharyngeal nerve.
The Stylohyoid Branch (ramus stylohyoideus) frequently arises in conjunction with the digastric branch; it is long
and slender, and enters the Stylohyoideus about its middle.
The Temporal Branches (rami temporales) cross the zygomatic arch to the temporal region, supplying the Auriculares anterior and superior, and joining with the zygomaticotemporal branch of the maxillary, and with the auriculotemporal
branch of the mandibular. The more anterior branches supply the Frontalis, the Orbicularis oculi, and the Corrugator, and
join the supraorbital and lacrimal branches of the ophthalmic.
The Zygomatic Branches (rami zygomatici; malar branches) run across the zygomatic bone to the lateral angle of
the orbit, where they supply the Orbicularis oculi, and join with filaments from the lacrimal nerve and the zygomaticofacial
branch of the maxillary nerve.
The Buccal Branches (rami buccales; infraorbital branches), of larger size than the rest, pass horizontally forward
to be distributed below the orbit and around the mouth. The superficial branches run beneath the skin and above the superficial muscles of the face, which they supply: some are distributed to the Procerus, joining at the medial angle of the
orbit with the infratrochlear and nasociliary branches of the ophthalmic. The deep branches pass beneath the Zygomaticus
and the Quadratus labii superioris, supplying them and forming an infraorbital plexus with the infraorbital branch of the
maxillary nerve. These branches also supply the small muscles of the nose. The lower deep branches supply the Buccinator
and Orbicularis oris, and join with filaments of the buccinator branch of the mandibular nerve.
The Mandibular Branch (ramus marginalis mandibulae) passes forward beneath the Platysma and Triangularis,
supplying the muscles of the lower lip and chin, and communicating with the mental branch of the inferior alveolar nerve.
The Cervical Branch (ramus colli) runs forward beneath the Platysma, and forms a series of arches across the side
of the neck over the suprahyoid region. One branch descends to join the cervical cutaneous nerve from the cervical plexus;
others supply the Platysma.
The Glossopharyngeal Nerve (IX cranial) is similar to the vagus nerve as regards its central connections and is
usually described with it. It contains somatic sensory, sympathetic afferent, taste, somatic motor and sympathetic efferent
fibers. The afferent sensory fibers arise from cells in the superior ganglion and in the petrosal ganglion. The same uncertainty exists concerning the nuclei of termination and nuclei of origin of the various components as for the vagus.
(1) The somatic sensory fibers are few in number. Some are distributed with the auricular branch of the vagus to
the external ear; others probably pass to the pharynx and fauces. They are supposed to join the spinal tract of the trigeminal
and terminate in its nucleus. The connections are similar to those of the somatic sensory fibers of the vagus.
(2) Sympathetic afferent fibers from the pharynx and middle ear are supposed to terminate in the dorsal nucleus.
Connections are probably established with motor nuclei concerned in chewing and swallowing; very little is known, however, about the connections with other parts of the brain.
(3) Taste fibers from the tongue probably terminate in the nucleus of the tractus solitarius. These fibers together
with similar fibers from the facial (nervus intermedius) and the vagus are supposed to form the tractus solitarius and terminate in its nucleus. The central connections have been considered under the vagus.
(4) Somatic motor fibers to the Sylopharyngeus muscle arise in the upper end of the nucleus ambiguus. The existence of these fibers in the roots of the glossopharyngeal is uncertain, as there are other paths by which such fibers might
reach the glossopharyngeal from the vagus. The sources of impulses passing to the nucleus ambiguus are considered under
the vagus.
(5) Sympathetic efferent fibers (motor and secretory fibers) arise from the nucleus dorsalis. Some authors believe
that the secretory fibers to the parotid gland arise from a distinct nucleus, the inferior salivatory nucleus, situated near the
dorsal nucleus. The preganglionic fibers from this nucleus terminate in the otic ganglion; the postganglionic fibers from the
otic ganglion pass to the parotid gland.
Practice skills
Students are supposed to identify the following structures on the samples:
facial and intermediate nerves (VII pair)
glossopharyngeal nerve (IX pair)
Practice class 11. The vagus nerve (Х). The parasympathetic nervous system.
The aim: to learn the vagus nerve, its branches and objects of innervation; to learn the parasympathetic
nervous system, its differences from the sympathetic one.
Professional orientation: the knowledge of this topic is necessary for doctors of all specialities; it represents special interest for therapists, neurologists, neuropathologists and others.
The plan of the practice class:
A. Checking of the home assignment: oral quiz or written test control – 30 minutes.
B. Summary lecture on the topic by teacher – 30 minutes.
a) The general characteristic of the vagus nerve, its nuclei and ganglia.
b) The branches of the vagus nerve.
c) The characteristic if the parasympathetic nervous system.
C. Students’ self-taught time – 55 minutes
D. Home-task – 5 minutes
The Vagus Nerve (N. Vagus; Tenth Nerve; Pneumogastric Nerve)
The vagus nerve is composed of both motor and sensory fibers, and has a more extensive course and distribution
than any of the other cranial nerves, since it passes through the neck and thorax to the abdomen.
The vagus is attached by eight or ten filaments to the medulla oblongata in the groove between the olive and the inferior peduncle, below the glossopharyngeal. The sensory fibers arise from the cells of the jugular ganglion and ganglion
nodosum of the nerve, and, when traced into the medulla oblongata mostly end by arborizing around the cells of the inferior
part of a nucleus which lies beneath the ala cinerea in the lower part of the rhomboid fossa. These are the sympathetic afferent fibers. Some of the sensory fibers of the glossopharyngeal nerve have been seen to end in the upper part of this nucleus. A few of the sensory fibers of the vagus, probably taste fibers, descend in the fasciculus solitarius and end around its
cells. The somatic sensory fibers, few in number, from the posterior part of the external auditory meatus and the back of
the ear, probably join the spinal tract of the trigeminal as it descends in the medulla. The somatic motor fibers arise from
the cells of the nucleus ambiguus, already referred to in connection with the motor root of the glossopharyngeal nerve.
The sympathetic efferent fibers, distributed probably as preganglionic fibers to the thoracic and abdominal viscera,
i. e., as motor fibers to the bronchial tree, inhibitory fibers to the heart, motor fibers to the esophagus, stomach, small intestine and gall passages, and as secretory fibers to the stomach and pancreas, arise from the dorsal nucleus of the vagus.
The filaments of the nerve unite, and form a flat cord, which passes beneath the flocculus to the jugular foramen,
through which it leaves the cranium. In emerging through this opening, the vagus is accompanied by and contained in the
same sheath of dura mater with the accessory nerve, a septum separating them from the glossopharyngeal which lies in
front. In this situation the vagus presents a well-marked ganglionic enlargement, which is called the jugular ganglion
(ganglion of the root); to it the accessory nerve is connected by one or two filaments. After its exit from the jugular foramen the vagus is joined by the cranial portion of the accessory nerve, and enlarges into a second gangliform swelling,
called the ganglion nodosum (ganglion of the trunk); through this the fibers of the cranial portion of the accessory pass
without interruption, being principally distributed to the pharyngeal and superior laryngeal branches of the vagus, but some
of its fibers descend in the trunk of the vagus, to be distributed with the recurrent nerve and probably also with the cardiac
nerves.
The vagus nerve passes vertically down the neck within the carotid sheath, lying between the internal jugular vein
and internal carotid artery as far as the upper border of the thyroid cartilage, and then between the same vein and the common carotid artery to the root of the neck. The further course of the nerve differs on the two sides of the body.
On the right side, the nerve passes across the subclavian artery between it and the right innominate vein, and descends by the side of the trachea to the back of the root of the lung, where it spreads out in the posterior pulmonary plexus. From the lower part of this plexus two cords descend on the esophagus, and divide to form, with branches from the opposite nerve, the esophageal plexus. Below, these branches are collected into a single cord, which runs along the back of
the esophagus enters the abdomen, and is distributed to the postero-inferior surface of the stomach, joining the left side of
the celiac plexus, and sending filaments to the lienal plexus.
On the left side, the vagus enters the thorax between the left carotid and subclavian arteries, behind the left innominate vein. It crosses the left side of the arch of the aorta, and descends behind the root of the left lung, forming there the
posterior pulmonary plexus. From this it runs along the anterior surface of the esophagus, where it unites with the nerve
of the right side in the esophageal plexus, and is continued to the stomach, distributing branches over its anterosuperior
surface; some of these extend over the fundus, and others along the lesser curvature. Filaments from these branches enter
the lesser omentum, and join the hepatic plexus.
The Jugular Ganglion (ganglion jugulare; ganglion of the root) is of a grayish color, spherical in form, about 4
mm. in diameter.
Branches of Communication.—This ganglion is connected by several delicate filaments to the cranial portion of
the accessory nerve; it also communicates by a twig with the petrous ganglion of the glossopharyngeal, with the facial
nerve by means of its auricular branch, and with the sympathetic by means of an ascending filament from the superior cervical ganglion.
The Ganglion Nodosum (ganglion of the trunk; inferior ganglion) is cylindrical in form, of a reddish color, and 2.5
cm. in length. Passing through it is the cranial portion of the accessory nerve, which blends with the vagus below the ganglion.
Branches of Communication.—This ganglion is connected with the hypoglossal, the superior cervical ganglion of
the sympathetic, and the loop between the first and second cervical nerves.
Branches of Distribution.—The branches of distribution of the vagus are:
In the Jugular Fossa – Meningeal; Auricular.
In the Neck – Pharyngeal; Superior laryngeal; Recurrent; Superior cardiac.
In the Thorax - Inferior cardiac; Anterior bronchial; Posterior bronchial; Esophageal.
In the Abdomen – Gastric; Celiac; Hepatic.
The Meningeal Branch (ramus meningeus; dural branch) is a recurrent filament given off from the jugular ganglion; it is distributed to the dura mater in the posterior fossa of the base of the skull.
The Auricular Branch (ramus auricularis; nerve of Arnold) arises from the jugular ganglion, and is joined soon after its origin by a filament from the petrous ganglion of the glossopharyngeal; it passes behind the internal jugular vein, and
enters the mastoid canaliculus on the lateral wall of the jugular fossa. Traversing the substance of the temporal bone, it
crosses the facial canal about 4 mm. above the stylomastoid foramen, and here it gives off an ascending branch which joins
the facial nerve. The nerve reaches the surface by passing through the tympanomastoid fissure between the mastoid process
and the tympanic part of the temporal bone, and divides into two branches: one joins the posterior auricular nerve, the other
is distributed to the skin of the back of the auricula and to the posterior part of the external acoustic meatus.
The Pharyngeal Branch (ramus pharyngeus), the principal motor nerve of the pharynx, arises from the upper part
of the ganglion nodosum, and consists principally of filaments from the cranial portion of the accessory nerve. It passes
across the internal carotid artery to the upper border of the Constrictor pharyngis medius, where it divides into numerous
filaments, which join with branches from the glossopharyngeal, sympathetic, and external laryngeal to form the pharyngeal plexus. From the plexus, branches are distributed to the muscles and mucous membrane of the pharynx and the muscles
of the soft palate, except the Tensor veli palatini. A minute filament descends and joins the hypoglossal nerve as it winds
around the occipital artery.
The Superior Laryngeal Nerve (n. laryngeus superior) larger than the preceding, arises from the middle of the
ganglion nodosum and in its course receives a branch from the superior cervical ganglion of the sympathetic. It descends,
by the side of the pharynx, behind the internal carotid artery, and divides into two branches, external and internal.
The external branch (ramus externus), the smaller, descends on the larynx, beneath the Sternothyreoideus, to supply the Cricothyreoideus. It gives branches to the pharyngeal plexus and the Constrictor pharyngis inferior, and communicates with the superior cardiac nerve, behind the common carotid artery.
The internal branch (ramus internus) descends to the hyothyroid membrane, pierces it in company with the superior laryngeal artery, and is distributed to the mucous membrane of the larynx. Of these branches some are distributed to the
epiglottis, the base of the tongue, and the epiglottic glands; others pass backward, in the aryepiglottic fold, to supply the
mucous membrane surrounding the entrance of the larynx, and that lining the cavity of the larynx as low down as the vocal
folds. A filament descends beneath the mucous membrane on the inner surface of the thyroid cartilage and joins the recurrent nerve.
The Recurrent Nerve (n. recurrens; inferior or recurrent laryngeal nerve) arises, on the right side, in front of the
subclavian artery; winds from before backward around that vessel, and ascends obliquely to the side of the trachea behind
the common carotid artery, and either in front of or behind the inferior thyroid artery. On the left side, it arises on the left of
the arch of the aorta, and winds below the aorta at the point where the ligamentum arteriosum is attached, and then ascends
to the side of the trachea. The nerve on either side ascends in the groove between the trachea and esophagus, passes under
the lower border of the Constrictor pharyngis inferior, and enters the larynx behind the articulation of the inferior cornu of
the thyroid cartilage with the cricoid; it is distributed to all the muscles of the larynx, excepting the Cricothyreoideus. It
communicates with the internal branch of the superior laryngeal nerve, and gives off a few filaments to the mucous membrane of the lower part of the larynx.
As the recurrent nerve hooks around the subclavian artery or aorta, it gives off several cardiac filaments to the deep
part of the cardiac plexus. As it ascends in the neck it gives off branches, more numerous on the left than on the right side,
to the mucous membrane and muscular coat of the esophagus; branches to the mucous membrane and muscular fibers of
the trachea; and some pharyngeal filaments to the Constrictor pharyngis inferior.
The Superior Cardiac Branches (rami cardiaci superiores; cervical cardiac branches), two or three in number,
arise from the vagus, at the upper and lower parts of the neck.
The upper branches are small, and communicate with the cardiac branches of the sympathetic. They can be traced
to the deep part of the cardiac plexus.
The lower branch arises at the root of the neck, just above the first rib. That from the right vagus passes in front or
by the side of the innominate artery, and proceeds to the deep part of the cardiac plexus; that from the left runs down across
the left side of the arch of the aorta, and joins the superficial part of the cardiac plexus.
The Inferior Cardiac Branches (rami cardiaci inferiores; thoracic cardiac branches), on the right side, arise from
the trunk of the vagus as it lies by the side of the trachea, and from its recurrent nerve; on the left side from the recurrent
nerve only; passing inward, they end in the deep part of the cardiac plexus.
The Anterior Bronchial Branches (rami bronchiales anteriores; anterior or ventral pulmonary branches), two or
three in number, and of small size, are distributed on the anterior surface of the root of the lung. They join with filaments
from the sympathetic, and form the anterior pulmonary plexus.
The Posterior Bronchial Branches (rami bronchiales posteriores; posterior or dorsal pulmonary branches), more
numerous and larger than the anterior, are distributed on the posterior surface of the root of the lung; they are joined by
filaments from the third and fourth (sometimes also from the first and second) thoracic ganglia of the sympathetic trunk,
and form the posterior pulmonary plexus. Branches from this plexus accompany the ramifications of the bronchi through
the substance of the lung.
The Esophageal Branches (rami aesophagei) are given off both above and below the bronchial branches; the lower
are numerous and larger than the upper. They form, together with the branches from the opposite nerve, the esophageal
plexus. From this plexus filaments are distributed to the back of the pericardium.
The Gastric Branches (rami gastrici) are distributed to the stomach. The right vagus forms the posterior gastric
plexus on the postero-inferior surface of the stomach and the left the anterior gastric plexus on the antero-superior surface.
The Celiac Branches (rami caeliaci) are mainly derived from the right vagus: they join the celiac plexus and
through it supply branches to the pancreas, spleen, kidneys, suprarenal bodies, and intestine.
The Hepatic Branches (rami hepatici) arise from the left vagus: they join the hepatic plexus and through it are
conveyed to the liver.
Parasympathetic system. The fibers of the central parasympathetic neurons pass to parasympathetic ganglia in the head
region in various cranial nerves. There a relay takes place to postganglionic fibers, which innervate the effector organ The
vagus, as the principal nerve of the parasympathetic system, descends together with the large cervical vessels (neurovascular trunk of the neck) and, after passing through the superior aperture of the thorax, it divides into a plexus in the region of
the thoracic and abdominal viscera.
Cells situated in the intermediolateral nucleus and the intermediomedial nucleus of the sacral cord send their axons through
the 3rd and 4th sacral nerves, to the pudendal nerve from which they pass as the pelvic nerves into the inferior hypogastric
plexus and to the pelvic organs (bladder, rectum and genitalia) Synapses with postganglionic fibers are found in the inferior
hypogastric plexus, or in small ganglia in the various organ plexuses
The Cranial Parasympathetics—The cranial parasympathetics include parasympathetic efferent fibers in the oculomotor, facial, glossopharyngeal and vagus nerves, as well as parasympathetic afferent in the last three nerves.
The Oculomotor Nerve (III cranial) contains somatic motor fibers to the Obliquus inferior, Rectus inferior, Rectus
superior, Levator palpebrae superioris and Rectus medialis muscles and parasympathetic efferent fibers (preganglionic fibers) to the ciliary ganglion. The postganglionic fibers connected with these supply the ciliary muscle and the sphincter of
the iris. The axons arise from the nucleus of the oculomotor nerve and pass in bundles through the posterior longitudinal
bundle, the tegmentum, the red nucleus and the medial margin of the substantia nigra in a series of curves and finally
emerge from the oculomotor sulcus on the medial side of the cerebral peduncle.
The Parasympathetic Efferent Fibers of the Oculomotor Nerve probably arise from cells in the anterior part of
the oculomotor nucleus which is located in the tegmentum of the mid-brain. These preganglionic fibers run with the third
nerve into the orbit and pass to the ciliary ganglion where they terminate by forming synapses with parasympathetic motor
neurons whose axons, postganglionic fibers, proceed as the short ciliary nerves to the eyeball. Here they supply motor fibers to the Ciliaris muscle and the Sphincter pupillae muscle. So far as known there are no parasympathetic afferent fibers
connected with the nerve.
The oculomotor nucleus lies in the gray substance of the floor of the cerebral aqueduct subjacent to the superior
colliculus and extends in front of the aqueduct a short distance into the floor of the third ventricle. The inferior end is continuous with the trochlear nucleus. It is from 6 to 10 mm. in length. It is intimately related to the posterior longitudinal bundle which lies against its ventro-lateral aspect and many of its cells lie among the fibers of the posterior longitudinal bundle. The nucleus of the oculomotor nerve contains several distinct groups of cells which differ in size and appearance from
each other and are supposed to send their axons each to a separate muscle. Much uncertainty still exists as to which group
supplies which muscle. There are seven of these groups or nuclei on either side of the midline and one medial nucleus. The
cells of the anterior nuclei are smaller and are supposed to give off the parasympathetic efferent axons. The majority of
fibers arise from the nucleus of the same side some, however, cross from the opposite side and are supposed to supply the
Rectus medialis muscle. Since oculomotor and abducens nuclei are intimately connected by the posterior longitudinal bundle this decussation of fibers to the Medial rectus may facilitate the conjugate movements of the eyes in which the Medial
and Lateral recti are especially involved.
Many collaterals and terminals are given off to the oculomotor nucleus from the posterior longitudinal bundle and
thus connect it with the vestibular nucleus, the trochlear and abducens nuclei and probably with other cranial nuclei. Fibers
from the visual reflex center in the superior colliculus pass to the nucleus. It is also connected with the cortex of the occipital lobe of the cerebrum by fibers which pass through the optic radiation. The pathway for voluntary motor impulses is
probably similar to that for the abducent nerve.
The Facial Nerve.
The Parasympathetic Efferent Fibers of the Facial Nerve are supposed to arise from the small cells of the facial
nucleus. According to some authors the fibers to the salivary glands arise from a special nucleus, the superior salivatory
nucleus, consisting of cells scattered in the reticular formation, dorso-medial to the facial nucleus. These preganglionic fibers are distributed partly through the chorda tympani and lingual nerves to the submaxillary ganglion where they terminate
about the cell bodies of neurons whose axons as postganglionic fibers conduct secretory and vasodilotar impulses to the
submaxillary and sublingual glands. Other preganglionic fibers of the facial nerve pass via the great superficial petrosal
nerve to the sphenopalatine ganglion where they form synapses with neurons whose postganglionic fibers are distributed
with the superior maxillary nerve as vasodilator and secretory fibers to the mucous membrane of the nose, soft palate, tonsils, uvula, roof of the mouth, upper lips and gums, parotid and orbital glands.
There are supposed to be a few parasympathetic afferent fibers connected with the facial nerve, whose cell bodies lie
in the geniculate ganglion, but very little is known about them.
Parasympathetic efferent fibers (preganglionic fibers) arise according to some authors from the small cells of the facial nucleus, or according to others from a special nucleus of cells scattered in the reticular formation, dorso-medial to the
facial nucleus. This is sometimes called the superior salivatory nucleus. These preganglionic fibers are distributed partly
via the chorda tympani and lingual nerves to the submaxillary ganglion, thence by postganglionic (vasodilator) fibers to the
submaxillary and sublingual glands. Some of the preganglionic fibers pass to the sphenopalatine ganglion via the great superficial petrosal nerve.
The parasympathetic afferent fibers are likewise few in number and of unknown termination.
The Glossopharyngeal Nerve.
The Parasympathetic Afferent Fibers of the Glossopharyngeal Nerve are supposed to arise either in the dorsal
nucleus (nucleus ala cinerea) or in a distinct nucleus, the inferior salivatory nucleus, situated near the dorsal nucleus. These
preganglionic fibers pass into the tympanic branch of the glossopharyngeal and then with the small superficial petrosal
nerve to the otic ganglion. Postganglionic fibers, vasodilator and secretory fibers, are distributed to the parotid gland, to the
mucous membrane and its glands on the tongue, the floor of the mouth, and the lower gums.
Parasympathetic Afferent Fibers, whose cells of origin lie in the superior or inferior ganglion of the trunk, are
supposed to terminate in the dorsal nucleus. Very little is known of the peripheral distribution of these fibers.
Parasympathetic afferent fibers from the pharynx and middle ear are supposed to terminate in the dorsal nucleus.
Connections are probably established with motor nuclei concerned in chewing and swallowing; very little is known, however, about the connections with other parts of the brain.
Parasympathetic efferent fibers (motor and secretory fibers) arise from the nucleus dorsalis. Some authors believe
that the secretory fibers to the parotid gland arise from a distinct nucleus, the inferior salivatory nucleus, situated near the
dorsal nucleus. The preganglionic fibers from this nucleus terminate in the otic ganglion; the postganglionic fibers from the
otic ganglion pass to the parotid gland.
The Vagus Nerve.
Parasympathetic efferent fibers arise from cells in the dorsal nucleus (nucleus of the ala cinerea). These are preganglionic fibers of the parasympathetic system and all terminate in parasympathetic ganglia from which postganglionic
fibers are distributed to various organs, i. e., motor fibers to the esophagus, stomach, small intestine, gallbladder, and to the
lungs; inhibitory fibers to the heart; secretory fibers to the stomach and pancreas. The dorsal nucleus not only receives terminals of parasympathetic afferent fibers for reflexes but undoubtedly receives terminals and collaterals from many other
sources, but the exact pathways are at present unknown.
The Parasympathetic Efferent Fibers of the Vagus Nerve are supposed to arise in the dorsal nucleus (nucleus ala cinerea). These preganglionic fibers are all supposed to end in parasympathetic ganglia situated in or near the organs supplied
by the vagus parasympathetics. The inhibitory fibers to the heart probably terminate in the small ganglia of the heart wall
especially the atrium, from which inhibitory postganglionic fibers are distributed to the musculature. The preganglionic
motor fibers to the esophagus, the stomach, the small intestine, and the greater part of the large intestine are supposed to
terminate in the plexuses of Auerbach, from which postganglionic fibers are distributed to the smooth muscles of these organs. Other fibers pass to the smooth muscles of the bronchial tree and to the gall-bladder and its ducts. In addition the vagus is believed to contain secretory fibers to the stomach and pancreas. It probably contains many other efferent fibers than
those enumerated above.
The parasympathetic afferent fibers are usually described as terminating in the dorsal nucleus of the vagus and
glossopharyngeal. Some authors, however, believe they join the tractus solitarius and terminate in its nucleus. These afferent fibers convey impulses from the heart, the pancreas, and probably from the stomach, esophagus and respiratory tract.
Their terminals in the dorsal nucleus come into relation with neurons whose axons probably descend into the spinal cord,
conveying impulses to the motor nuclei supplying fibers to the muscles of respiration, i. e., the phrenic nerve and the nerves
to the intercostal and levatores costarum muscles. Other axons probably convey vasomotor impulses to certain parasympathetic efferent neurons throughout the spinal cord. The dorsal nucleus (nucleus of the ala cinerea) and the posterior continuation of it into the commissural nucleus of the ala cinerea constitute probably the so-called respiratory and vaso-motor center of the medulla. The shorter reflex neurons of the dorsal nucleus probably effect connections either directly or indirectly
with motor cells of the vagus itself and other cranial nerves.
Parasympathetic Afferent Fibers of the Vagus, whose cells of origin lie in the jugular ganglion or the ganglion
nodosum, probably terminate in the dorsal nucleus of the medulla oblongata or according to some authors in the nucleus of
the tractus solitarius. Peripherally the fibers are supposed to be distributed to the various organs supplied by the parasympathetic efferent fibers.
The Sacral Parasympathetics—The Sacral Parasympathetic Efferent Fibers leave the spinal cord with the anterior roots of the second, third and fourth sacral nerves. These small medullated preganglionic fibers are collected together
in the pelvis into the nervus erigentes or pelvic nerve which proceeds to the hypogastric or pelvic plexuses from which
postganglionic fibers are distributed to the pelvic viscera. Motor fibers pass to the smooth muscle of the descending colon,
rectum, anus and bladder. Vasodilators are distributed to these organs and to the external genitalia, while inhibitory fibers
probably pass to the smooth muscles of the external genitalia. Afferent parasympathetic fibers conduct impulses from the
pelvic viscera to the second, third and fourth sacral nerves. Their cells of origin lie in the spinal ganglia.
Practice skills
Students are supposed to identify the following structures on the samples:
Vagus nerve (X pair)
- anterior et posterior vagal trunks
- recurrent laryngeal nerve
Self-taught class 8. Review of the peripheral nervous system. Review of cranial nerves.
The aim: to learn the general characteristic of the peripheral nervous system and cranial nerves.
Professional orientation: the knowledge of this topic is necessary for doctors of all specialities; it represents special interest for therapists, neurologists, neuropathologists and others.
The plan of the self-taught class:
A. Revise the division of the nervous system into the central and peripheral.
B. Revise the general characteristic of spinal nerves.
C. Revise the projection of cranial nerves’ nuclei on the dorsal surface of the brainstem and the places where
cranial nerves leave the brain.
D. Learn the general characteristic of the cranial nerves.
E. Compare the spinal and cranial nerves.
F. Find out the connection of cranial nerves’ nuclei with other subcortical ganglia.
The cranial nerves.
The cranial nerves are more varied in their composition than the spinal nerves. Some, for example, contain somatic
motor fibers only, others contain the various types of fibers found in the spinal nerves, namely, somatic motor, sympathetic
efferent, somatic sensory and sympathetic sensory. In addition there are included the nerves of the special senses, namely,
the nerves of smell, sight, hearing, equilibration and taste.
The Hypoglossal Nerve (XII cranial) consists of somatic motor fibers only and supplies the muscles of the tongue.
Its axons arise from cells in the hypoglossal nucleus and pass forward between the white reticular formation and the gray
reticular formation to emerge from the antero-lateral sulcus of the medulla. The hypoglossal nuclei of the two sides are
connected by many commissural fibers and also by dendrites of motor cells which extend across the midline to the opposite
nucleus. The hypoglossal nucleus receives either directly or indirectly numerous collaterals and terminals from the opposite
pyramidal tract (cortico-bulbar or cerebrobulbar fibers) which convey voluntary motor impulses from the cerebral cortex.
Many reflex collaterals enter the nucleus from the secondary sensory paths of the trigeminal and vagus and probably also
from the nervus intermedius and the glossopharyngeal. Collaterals from the posterior longitudinal bundle and the ventral
longitudinal bundle are said to pass to the nucleus.
The Accessory Nerve (XI cranial) contains somatic motor fibers. The spinal part arises from lateral cell groups in
the anterior column near its dorso-lateral margin in the upper five or six segments of the cord, its roots pass through the
lateral funiculus to the lateral surface of the cord. It supplies the Trapezius and Sternocleidomastoideus. The cranial part
arises from the nucleus ambiguus, the continuation in the medulla oblongata of the lateral cell groups of the anterior column of the spinal cord from which the spinal part has origin. The upper part of the nucleus ambiguus gives motor fibers to
the vagus and glossopharyngeal nerves. The cranial part sends it fibers through the vagus to the laryngeal nerves to supply
the muscles of the larynx. The root fibers of the cranial part of the accessory nerve pass anterior to the spinal tract of the
trigeminal while those of the vagus pass through or dorsal to the trigeminal root, and emerge in the line of the posterolateral sulcus. The nucleus of origin of the spinal part undoubtedly receives either directly or indirectly terminals and collaterals controlling voluntary movements from the pyramidal tracts. It is probable that terminals and collaterals reach the
nucleus either directly or indirectly from the rubrospinal and the vestibulospinal tracts. It is also connected indirectly with
the spinal somatic sensory nerves by association fibers of the proper fasciculi. The cranial part receives indirectly or directly terminals and collaterals from the opposite pyramidal tract and form the terminal sensory nuclei of the cranial nerves. A
few fibers of the cranial part are said to arise in the dorsal nucleus of the vagus and are thus sympathetic efferent. They are
said to join the vagus nerve.
The Vagus Nerve (X cranial) contains somatic sensory, sympathetic afferent, somatic motor, sympathetic efferent
and (taste fibers?). The afferent fibers (somatic sensory, sympathetic, and taste) have their cells of origin in the jugular ganglion and in the nodosal ganglion (ganglion of the trunk) and on entering the medulla divide into ascending and descending
branches as do the sensory fibers of the posterior roots of the spinal nerves after they enter the spinal cord.
(1) The somatic sensory fibers are few in number, convey impulses from a limited area of the skin on the back of
the ear and posterior part of the external auditory meatus, and probably join the spinal tract of the trigeminal nerve to terminate in its nucleus. Connections are probably established through the central path of the trigeminal with the thalamus and
somatic sensory area of the cortex for the conscious recognition of impulses. The descending fibers in the spinal tract of the
trigeminal terminating in the nucleus of the tract probably establish relations through connecting neurons with motor nuclei
in the anterior column of the spinal cord and with motor nuclei of the medulla.
(2) The sympathetic afferent fibers are usually described as terminating in the dorsal nucleus of the vagus and
glossopharyngeal. Some authors, however, believe they join the tractus solitarius and terminate in its nucleus. These afferent fibers convey impulses from the heart, the pancreas, and probably from the stomach, esophagus and respiratory tract.
Their terminals in the dorsal nucleus come into relation with neurons whose axons probably descend into the spinal cord,
conveying impulses to the motor nuclei supplying fibers to the muscles of respiration, i. e., the phrenic nerve and the nerves
to the intercostal and levatores costarum muscles. Other axons probably convey vasomotor impulses to certain sympathetic
efferent neurons throughout the spinal cord. The dorsal nucleus (nucleus of the ala cinerea) and the posterior continuation
of it into the commissural nucleus of the ala cinerea constitute probably the so-called respiratory and vaso-motor center of
the medulla. The shorter reflex neurons of the dorsal nucleus probably effect connections either directly or indirectly with
motor cells of the vagus itself and other cranial nerves.
(3) Taste fibers conducting impulses from the epiglottis and larynx are supposed to pass in the vagus and to join
the tractus solitarius, finally terminating in the nucleus of the tractus solitarius. It is not certain that this nucleus represents
the primary terminal center for taste and some authors maintain that the taste fibers terminate in the dorsal nucleus. The
secondary ascending pathways from the primary gustatory nucleus to the cortex as well as the location of the cortical center
for taste are unknown. A gustatory center has been described near the anterior end of the temporal lobe. The nucleus of the
tractus solitarius is connected with motor centers of the pons, medulla and spinal cord for the reactions of mastication and
swallowing.
(4) Somatic motor fibers to the cross striated muscles of the pharynx and larynx arise in the nucleus ambiguus.
This nucleus undoubtedly receives either directly or indirectly collaterals or terminals from the opposite pyramidal tract
controlling the voluntary movements of the pharynx and larynx. The reflex pathways conveying impulses from the terminal
sensory nuclei are unknown, but probably form part of the intricate maze of fibers constituting the reticular formation.
(5) Sympathetic efferent fibers arise from cells in the dorsal nucleus (nucleus of the ala cinerea). These are preganglionic fibers of the sympathetic system and all terminate in sympathetic ganglia from which postganglionic fibers are
distributed to various organs, i. e., motor fibers to the esophagus, stomach, small intestine, gallbladder, and to the lungs;
inhibitory fibers to the heart; secretory fibers to the stomach and pancreas. The dorsal nucleus not only receives terminals
of sympathetic afferent fibers for reflexes but undoubtedly receives terminals and collaterals from many other sources, but
the exact pathways are at present unknown.
The Glossopharyngeal Nerve (IX cranial) is similar to the vagus nerve as regards its central connections and is
usually described with it. It contains somatic sensory, sympathetic afferent, taste, somatic motor and sympathetic efferent
fibers. The afferent sensory fibers arise from cells in the superior ganglion and in the petrosal ganglion. The same uncertainty exists concerning the nuclei of termination and nuclei of origin of the various components as for the vagus.
(1) The somatic sensory fibers are few in number. Some are distributed with the auricular branch of the vagus to
the external ear; others probably pass to the pharynx and fauces. They are supposed to join the spinal tract of the trigeminal
and terminate in its nucleus. The connections are similar to those of the somatic sensory fibers of the vagus.
(2) Sympathetic afferent fibers from the pharynx and middle ear are supposed to terminate in the dorsal nucleus.
Connections are probably established with motor nuclei concerned in chewing and swallowing; very little is known, however, about the connections with other parts of the brain.
(3) Taste fibers from the tongue probably terminate in the nucleus of the tractus solitarius. These fibers together
with similar fibers from the facial (nervus intermedius) and the vagus are supposed to form the tractus solitarius and terminate in its nucleus. The central connections have been considered under the vagus.
(4) Somatic motor fibers to the Sylopharyngeus muscle arise in the upper end of the nucleus ambiguus. The existence of these fibers in the roots of the glossopharyngeal is uncertain, as there are other paths by which such fibers might
reach the glossopharyngeal from the vagus. The sources of impulses passing to the nucleus ambiguus are considered under
the vagus.
(5) Sympathetic efferent fibers (motor and secretory fibers) arise from the nucleus dorsalis. Some authors believe
that the secretory fibers to the parotid gland arise from a distinct nucleus, the inferior salivatory nucleus, situated near the
dorsal nucleus. The preganglionic fibers from this nucleus terminate in the otic ganglion; the postganglionic fibers from the
otic ganglion pass to the parotid gland.
The Acoustic Nerve (VIII cranial) consists of two distinct nerves the cochlear nerve, the nerve of hearing, and the
vestibular nerve, the nerve of equilibration.
The Cochlear Nerve arises from bipolar cells in the spiral ganglion of the cochlea; the peripheral fibers end in the
organ of Corti, the central fibers bifurcate as they enter the cochlear nucleus; the short ascending branches end in the ventral portion of the nucleus, the longer descending branches terminate in the dorsal portion of the nucleus. From the dorsal
portion of the cochlear nucleus axons arise which pass across the dorsal aspect of the inferior peduncle and the floor of the
fourth ventricle, the striae medullares, to the median sulcus. Here they dip into the substance of the pons, cross the median
plane, and join the lateral lemniscus. Some of the fibers terminate in the superior olivary nucleus. The fibers of the striae
medullares are not always visible on the floor of the rhomboid fossa. From the ventral portion of the cochlear nucleus axons pass into the trapezoid body, here some of them end in the superior olivary nucleus of the same side, others cross the
midline and end in the superior olivary nucleus of the opposite side or pass by these nuclei, giving off collaterals to them,
and join the lateral lemniscus. Other fibers either terminate in or give off collaterals to the nucleus of the trapezoid body of
the same or the opposite side. Other fibers from the ventral portion of the cochlear nucleus pass dorsal to the inferior peduncle and then dip into the substance of the pons to join the trapezoid body or the superior olivary nucleus of the same
side. From the superior olivary nucleus of the same and opposite sides axons join the lateral lemniscus. Collaterals and
probably terminals also pass from the lateral lemniscus to other nuclei in its path and receive in turn axons from these nuclei. They are the accessory nucleus, the medial preolivary nucleus, the lateral preolivary or semilunar nucleus and the nucleus of the lateral lemniscus.
The trapezoid body consists of horizontal fibers in the ventral part of the formatio reticularis of the lower part of
the pons behind its deep transverse fibers and the pyramid bundles. The axons come from the dorsal and ventral portions of
the cochlear nucleus. After crossing the raphé, where they decussate with those from the opposite side, they turn upward to
form the lateral lemniscus. Fibers from the striae medullares contribute to the trapezoid body, in addition it sends terminals
or collaterals to and receives axons from the superior olivary nucleus, the nucleus of the trapezoid body, the lateral preolivary or semilunar nucleus and the mesial preolivary nucleus.
The cochlear nucleus, the terminal nucleus for the nerve of hearing, is usually described as consisting of a larger
dorsal nucleus on the dorsal and lateral aspect of the inferior peduncle forming a prominent projection, the acoustic tubercle, and a ventral or accessory cochlear nucleus more ventral to the inferior peduncle. The two nuclei are continuous and
are merely portions of one large nucleus. The axons from cells of the spiral ganglion of the cochlear nerve on reaching the
nucleus divide into ascending and descending branches which enter the ventral and dorsal nuclei respectively. Axons from
the large fusiform cells of the dorsal nucleus pass partly by way of the striae medullares to the trapezoid body and lateral
lemniscus and the nuclei associated with the former, and partly transversely beneath the inferior peduncle and spinal tract
of the trigeminal to the trapezoid body. Axons from the ventral cochlear nucleus pass partly by the striae medullares but for
the most part horizontally to the trapezoid body.
The superior olivary nucleus is a small mass of gray matter situated on the dorsal surface of the lateral part of the
trapezoid body. Some of its axons pass backward to the abducent nucleus, this bundle is known as the peduncle of the superior olivary nucleus. Other fibers from the nucleus join the posterior longitudinal bundle and terminate in the nuclei of
the trochlear and oculomotor nerves. The majority of its axons, after giving off collaterals to the nucleus itself join the lateral lemniscus of the same side, other axons pass in the trapezoid body toward the ventral portion of the cochlear nucleus.
The nucleus of the trapezoid body lies between the root fibers of the abducent nerve and the superior olivary nucleus. Its cells lie among the fibers of the trapezoid body. In it terminate fibers and collaterals of the trapezoid body which
come from the cochlear nucleus of the opposite and probably the same side and from the opposite trapezoid nucleus. They
terminate in the nucleus of the trapezoid body in diffuse arborizations and peculiar end plaques or acoustic calyces of yellowish color which fuse with the cell bodies. Its cells are round and of medium size; their axons pass into the trapezoid
body, cross the median line and probably join the lateral fillet.
The lateral preolivary or semilunar nucleus lies ventral to the superior olivary nucleus. In it end terminals and collaterals of the trapezoid body and probably fibers of the opposite cochlear nucleus. Its axons mingle with the trapezoid
body and join the lateral fillet.
The mesial preolivary nucleus is in contact with the ventral side of the nucleus of the trapezoid body. It receives
many collaterals from the trapezoid body. Its cells are smaller than those of the trapezoid nucleus, their axons join the lateral fillet.
The lateral lemniscus (lateral fillet), the continuation upward of the central path of hearing, consists of fibers which
come from the cochlear nuclei of the same and the opposite side by way of the trapezoid body and from the preolivary nuclei. It lies in the ventral or ventro-lateral part of the reticular formation of the pons, at first ventral then lateral to the median fillet. Above the pons these ascending fibers come to the surface at the side of the reticular formation in the trigonum
lemnisci and are covered by a layer of ependyma. This part of the lateral lemniscus is known as the fillet of Reil. On reaching the level of the inferior colliculus the dorsal fibers which overlie the superior peduncle decussate in the velum medullare anterius with similar fibers of the opposite side. Numerous small masses of cells are scattered along the path of the
lateral lemniscus above the superior olivary nucleus and constitute lower and upper nuclei of the lateral lemniscus. They
are supplied with many collaterals and possibly terminals from the fibers of the lemniscus. The axons of the lower nucleus
of the lateral lemniscus, which arise from the larger stellate or spindle-shaped cells, with long, smooth, much branched
dendrites, are said by some authors to join the lateral lemniscus, but according to Cajal they pass medially toward the
raphé; their termination is unknown. The cells of the upper nucleus of the lateral lemniscus are more scattered. The same
uncertainty exists in regard to their termination.
The fibers of the lateral lemniscus end by terminals or collaterals in the inferior colliculus and the medial geniculate
body. A few of the fibers are said to pass by the inferior colliculus to terminate in the middle portion of the stratum griseum
of the superior colliculus, and are probably concerned with reflex movements of the eyes depending on acoustic stimuli.
The inferior colliculi (lower or posterior quadrigeminal bodies) are important auditory reflex centers. Each consists
of a compact nucleus of gray matter covered by a superficial white layer and separated from the central gray matter about
the aqueduct by a thin, deep, white layer. Many of the axons which appear in the superficial white layer ascend through the
inferior brachium to the medial geniculate body. Others mainly from large cells in the dorso-mesial part of the nucleus pass
through the deep white layer into the tegmentum of the same and the opposite side and descend. Their termination is unknown, but they probably constitute an auditory reflex path to the lower motor centers, perhaps descending into the spinal
cord with the tectospinal fasciculus. Other axons are said to descend in the lateral lemniscus to the various nuclei in the
auditory path (Held) and probably to motor nuclei of the medulla and spinal cord.
The medial geniculate body receives terminals and collaterals from the lateral lemniscus (the central auditory path)
and also large numbers of axons from the inferior colliculus of the same side and a few from the opposite side. It is thus a
station in the central auditory path. A large proportion of its axons pass forward beneath the optic tract to join the corona
radiata and then sweep backward and lateralward as the auditory radiation to terminate in the cortex of the superior temporal gyrus. V. Monakow holds that Golgi cells type II are interpolated between the terminations of the incoming fibers to
the medial geniculate body and the cells located there which give rise to the fibers of the auditory radiation. the medial geniculate bodies are united by the long, slender commissure of Gudden. These fibers join the optic tract as it passes over
the edge of the medial geniculate and passes through the posterior part of the optic chiasma. It is probably a commissure
connected with the auditory system.
The Vestibular Nerve (vestibular root, VIII cranial) arise from the bipolar cells in the vestibular ganglion (Scarpa’s
ganglion). The peripheral fibers end in the semicircular canals, the saccule and the utricle, the end-organs concerned with
mechanism for the maintenance of bodily equilibrium. The central fibers enter the medulla oblongata and pass between the
inferior peduncle and the spinal tract of the trigeminal. They bifurcate into ascending and descending branches as do the
dorsal root fibers of all the spinal nerves and all afferent cranial nerves. The descending branches terminate in the dorsal
(medial) vestibular nucleus, the principal nucleus of the vestibular nerve. This nucleus is prolonged downward into a descending portion in which end terminals and collaterals of the descending branch. The ascending branches pass to Deiters’s
nucleus, to Bechterew’s nucleus and through the inferior peduncle of the cerebellum to the nucleus tecti of the opposite
side.
The dorsal vestibular nucleus (medial or principal nucleus) is a large mass of small cells in the floor of the fourth
ventricle under the area acustica, located partly in the medulla and partly in the pons. The striae medullares cross the upper
part of it. It is separated from the median plane by the nucleus intercalatus. Its axons pass into the posterior longitudinal
bundle of the same and the opposite side and ascend to terminate in the nucleus abducens of the same side and in the trochlear nucleus and the oculo-motor nucleus of the opposite side, and to the motor nuclei of the trigeminal on both sides. The
descending portion, the nucleus of the descending tract extends downward as far as the upper end of the nucleus gracilis,
and the decussation of the medial lemniscus. It is sometimes called the inferior vestibular nucleus. Many of its axons
cross the midline and probably ascend with the medial lemniscus to the ventro-lateral region of the thalamus.
The lateral vestibular nucleus (Deiters’s nucleus) is the continuation upward and lateralward of the principal nucleus, and in it terminate many of the ascending branches of the vestibular nerve. It consists of very large multipolar cells
whose axons form an important part of the posterior longitudinal bundle of the same and the opposite side. The axons bi-
furcate as they enter the posterior longitudinal bundle, the ascending branches send terminals and collaterals to the motor
nuclei of the abducens, trochlear and oculomotor nerves, and are concerned in coördinating the movements of the eyes with
alterations in the position of the head; the descending branches pass down in the posterior longitudinal bundle into the anterior funiculus of the spinal cord as the vestibulospinal fasciculus (anterior marginal bundle) and are distributed to motor
nuclei of the anterior column by terminals and collaterals. Other fibers are said to pass directly to the vestibulospinal fasciculus without passing into the posterior longitudinal bundle. The fibers which pass into the vestibulospinal fasciculus are
intimately concerned with equilibratory reflexes. Other axons from Deiters’s nucleus are supposed to cross and ascend in
the opposite medial lemniscus to the ventro-lateral nuclei of the thalamus; still other fibers pass into the cerebellum with
the inferior peduncle and are distributed to the cortex of the vermis and the roof nuclei of the cerebellum; according to Cajal they merely pass through the nucleus fastigii on their way to the cortex of the vermis and the hemisphere.
The superior vestibular nucleus (Bechterew’s nucleus) is the dorso-lateral part of the vestibular nucleus and receives collaterals and terminals from the ascending branches of the vestibular nerve. Its axons terminate in much the same
manner as do those from the lateral nucleus.
The Facial Nerve (VII cranial) consists of somatic sensory, sympathetic afferent, taste, somatic motor and sympathetic efferent fibers. The afferent or sensory fibers arise from cells in the geniculate ganglion. This portion of the nerve is
often described as the nervus intermedius.
(1) The somatic sensory fibers are few in number and convey sensory impulses from the middle ear region. Their
existence has not been fully confirmed. Their central termination is likewise uncertain, it is possible that they join the spinal
tract of the trigeminal as do the somatic sensory fibers of the vagus and glossopharyngeal.
(2) The sympathetic afferent fibers are likewise few in number and of unknown termination.
(3) Taste fibers convey impulses from the anterior two-thirds of the tongue via the chorda tympani. They are supposed to join the tractus solitarius and terminate in its nucleus. The central connections of this nucleus have already been
considered.
(4) Somatic motor fibers, supplying the muscles derived from the hyoid arch, arise from the large multipolar cells
of the nucleus of the facial nerve. This nucleus is serially homologous with the nucleus ambiguus and lateral part of the
anterior column of the spinal cord. Voluntary impulses from the cerebral cortex are conveyed by terminals and collaterals
of the pyramidal tract of the opposite side, indirectly, that is with the interpolation of a connecting neuron, to the facial nucleus. This nucleus undoubtedly receives many reflex fibers from various sources, i. e., from the superior colliculus via the
ventral longitudinal bundle (tectospinal fasciculus) for optic reflexes; from the inferior colliculus via the auditory reflex
path; and indirectly from the terminal sensory nuclei of the brain-stem. Through the posterior longitudinal bundle it is intimately connected with other motor nuclei of the brain-stem.
(5) Sympathetic efferent fibers (preganglionic fibers) arise according to some authors from the small cells of the
facial nucleus, or according to others from a special nucleus of cells scattered in the reticular formation, dorso-medial to the
facial nucleus. This is sometimes called the superior salivatory nucleus. These preganglionic fibers are distributed partly
via the chorda tympani and lingual nerves to the submaxillary ganglion, thence by postganglionic (vasodilator) fibers to the
submaxillary and sublingual glands. Some of the preganglionic fibers pass to the sphenopalatine ganglion via the great superficial petrosal nerve.
The Abducens Nerve (VI cranial) contains somatic motor fibers only which supply the lateral rectus muscle of the
eye. The fibers arise from the nucleus of the abducens nerve and pass ventrally through the formatio reticularis of the pons
to emerge in the transverse groove between the caudal edge of the pons and the pyramid. The nucleus is serially homologous with the nuclei of the trochlear and oculomotor above and with the hypoglossal and medial part of the anterior column
of the spinal cord below. It is situated close to the floor of the fourth ventricle, just above the level of the striae medullares.
Voluntary impulses from the cerebral cortex are conducted by the pyramidal tract fibers (corticopontine fibers). These
fibers probably terminate in relation with association neurons which control the coördinated action of all the eye muscles.
This association and coördination mechanism is interposed between the terminals and collaterals of the voluntary fibers and
the neurons within the nuclei of origin of the motor fibers to the eye muscles. The fibers of the posterior longitudinal bundle are supposed to play an important role in the coördination of the movements of the eyeball. Whether it is concerned
only with coördinations between the vestibular apparatus and the eye or with more extensive coördinations is unknown.
Many fibers of the posterior longitudinal bundle have their origin in the terminal nuclei of the vestibular nerve and from the
posterior longitudinal bundle many collaterals and terminals are given off to the abducent nucleus as well as to the trochlear
and oculomotor nuclei. The abducens nucleus probably receives collaterals and terminals from the ventral longitudinal
bundle (tectospinal fasciculus); fibers which have their origin in the superior colliculus, the primary visual center, and are
concerned with visual reflexes. Others probably come from the reflex auditory center in the inferior colliculus and from
other sensory nuclei of the brain-stem.
The Trigeminal Nerve (V cranial) contains somatic motor and somatic sensory fibers. The motor fibers arise in the
motor nucleus of the trigeminal and pass ventro-laterally through the pons to supply the muscles of mastication. The sensory fibers arise from the unipolar cells of the semilunar ganglion; the peripheral branches of the T-shaped fibers are distributed to the face and anterior two-thirds of the head; the central fibers pass into the pons with the motor root and bifurcate
into ascending and descending branches which terminate in the sensory nuclei of the trigeminal.
The motor nucleus of the trigeminal is situated in the upper part of the pons beneath the lateral angle of the fourth
ventricle. It is serially homologous with the facial nucleus and the nucleus ambiguus (motor nucleus of the vagus and glossopharyngeal) which belong to the motor nuclei of the lateral somatic group. The axons arise from large pigmented multipolar cells. The motor nucleus receives reflex collaterals and terminals, (1) from the terminal nucleus of the trigeminal of
the same and a few from the opposite side, via the central sensory tract (trigeminothalamic tract); (2) from the mesencephalic root of the trigeminal; (3) from the posterior longitudinal bundle; (4) and probably from fibers in the formatio reticu-
laris. It also receives collaterals and terminals from the opposite pyramidal tract (corticopontine fibers) for voluntary
movements. There is probably a connecting or association neuron interposed between these fibers and the motor neurons.
The terminal sensory nucleus consists of an enlarged upper end, the main sensory nucleus, and a long more slender descending portion which passes down through the pons and medulla to become continuous with the dorsal part of the
posterior column of the gray matter especially the substantia gelatinosa of the spinal cord. This descending portion consists
mainly of substantia gelatinosa and is called the nucleus of the spinal tract of the trigeminal nerve.
The main sensory nucleus lies lateral to the motor nucleus beneath the superior peduncle. It receives the short ascending branches of the sensory root. The descending branches which form the tractus spinalis, pass down through the
pons and medulla on the lateral side of the nucleus of the tractus spinalis, in which they end by collaterals and terminals,
into the spinal cord on the level of the second cervical segment. It decreases rapidly in size as it descends. At first it is located between the emergent part of the facial nerve and the vestibular nerve, then between the nucleus of the facial nerve
and the inferior peduncle. Lower down in the upper part of the medulla it lies beneath the inferior peduncle and is broken
up into bundles by the olivocerebellar fibers and the roots of the ninth and tenth cranial nerves. Finally it comes to the surface of the medulla under the tubercle of Rolando and continues in this position lateral to the fasciculus cuneatus as far as
the upper part of the cervical region where it disappears.
The cells of the sensory nucleus are of large and medium size and send their axons into the formatio reticularis
where they form a distinct bundle, the central path of the trigeminal (trigeminothalamic tract), which passes upward
through the formatio reticularis and tegmentum to the ventro-lateral part of the thalamus. Most of the fibers cross to the
trigeminothalamic tract of the opposite side. This tract lies dorsal to the medial fillet; approaches close to it in the tegmentum and terminates in a distinct part of the thalamus. From the thalamus impulses are conveyed to the somatic sensory area
of the cortex by axons of cells in the thalamus through the internal capsule and corona radiata. Many collaterals are given
off in the medulla and pass from the trigeminothalamic tract to the motor nuclei, especially to the nucleus ambiguus, the
facial nucleus and the motor nucleus of the trigeminal.
The somatic sensory fibers of the vagus, the glossopharyngeal and the facial nerves probably end in the nucleus of
the descending tract of the trigeminal and their cortical impulses are probably carried up in the central sensory path of the
trigeminal.
The mesencephalic root (descending root of the trigeminal) arises from unipolar cells arranged in scattered groups
in a column at the lateral edge of the central gray matter surrounding the upper end of the fourth ventricle and the cerebral
aqueduct. They have usually been considered as motor fibers that join the motor root, but Johnston claims that they join the
sensory root of the trigeminal, that they develop in the alar, not in the basal lamina, and that the pear-shaped unipolar cells
are sensory in type.
The Trochlear Nerve (IV cranial) contains somatic motor fibers only. It supplies the superior oblique muscle of the
eye. Its nucleus of origin, trochlear nucleus, is a small, oval mass situated in the ventral part of the central gray matter of
the cerebral aqueduct at the level of the upper part of the inferior colliculus. The axons from the nucleus pass downward in
the tegmentum toward the pons, but turn abruptly dorsalward before reaching it, and pass into the superior medullary velum, in which they cross horizontally, to decussate with the nerve of the opposite side, and emerges from the surface of the
velum, immediately behind the inferior colliculus. The cells of the trochlear nucleus are large, irregular and yellowish in
color. The nuclei of the two sides are separated by the raphé through which dendrites extend from one nucleus to the other.
They receive many collaterals and terminals from the posterior longitudinal bundle which lies on the ventral side of the
nucleus.
There are no branches from the fibers of the pyramidal tracts to these nuclei; the volitional pathway must be an indirect one, as is the case with other motor nuclei.
The Oculomotor Nerve (III cranial) contains somatic motor fibers to the Obliquus inferior, Rectus inferior, Rectus
superior, Levator palpebrae superioris and Rectus medialis muscles and sympathetic efferent fibers (preganglionic fibers)
to the ciliary ganglion. The postganglionic fibers connected with these supply the ciliary muscle and the sphincter of the
iris. The axons arise from the nucleus of the oculomotor nerve and pass in bundles through the posterior longitudinal bundle, the tegmentum, the red nucleus and the medial margin of the substantia nigra in a series of curves and finally emerge
from the oculomotor sulcus on the medial side of the cerebral peduncle.
The oculomotor nucleus lies in the gray substance of the floor of the cerebral aqueduct subjacent to the superior
colliculus and extends in front of the aqueduct a short distance into the floor of the third ventricle. The inferior end is continuous with the trochlear nucleus. It is from 6 to 10 mm. in length. It is intimately related to the posterior longitudinal bundle which lies against its ventro-lateral aspect and many of its cells lie among the fibers of the posterior longitudinal bundle. The nucleus of the oculomotor nerve contains several distinct groups of cells which differ in size and appearance from
each other and are supposed to send their axons each to a separate muscle. Much uncertainty still exists as to which group
supplies which muscle. There are seven of these groups or nuclei on either side of the midline and one medial nucleus. The
cells of the anterior nuclei are smaller and are supposed to give off the sympathetic efferent axons. The majority of fibers
arise from the nucleus of the same side some, however, cross from the opposite side and are supposed to supply the Rectus
medialis muscle. Since oculomotor and abducens nuclei are intimately connected by the posterior longitudinal bundle this
decussation of fibers to the Medial rectus may facilitate the conjugate movements of the eyes in which the Medial and Lateral recti are especially involved.
Many collaterals and terminals are given off to the oculomotor nucleus from the posterior longitudinal bundle and
thus connect it with the vestibular nucleus, the trochlear and abducens nuclei and probably with other cranial nuclei. Fibers
from the visual reflex center in the superior colliculus pass to the nucleus. It is also connected with the cortex of the occipital lobe of the cerebrum by fibers which pass through the optic radiation. The pathway for voluntary motor impulses is
probably similar to that for the abducent nerve.
The Optic Nerve or Nerve of Sight (II cranial) consists chiefly of coarse fibers which arise from the ganglionic
layer of the retina. They constitute the third neuron in the series composing the visual path and are supposed to convey only
visual impressions. A number of fine fibers also pass in the optic nerve from the retina to the primary centers and are supposed to be concerned in the pupillary reflexes. There are in addition a few fibers which pass from the brain to the retina;
they are supposed to control chemical changes in the retina and the movements of the pigment cells and cones. Each optic
nerve has, according to Salzer, about 500,000 fibers.
In the optic chiasma the nerves from the medial half of each retina cross to enter the opposite optic tract, while the
nerves from the lateral half of each retina pass into the optic tract of the same side. The crossed fibers tend to occupy the
medial side of each optic nerve, but in the chiasma and in the optic tract they are more intermingled. The optic tract is attached to the tuber cinereum and lamina terminalis and also to the cerebral peduncle as it crosses obliquely over its under
surface. These are not functional connections. A small band of fibers from the medial geniculate body joins the optic tract
as the latter passes over it and crosses to the opposite tract and medial geniculate body in the posterior part of the chiasma.
This is the commissure of Gudden and is probably connected with the auditory system.
Most of the fibers of the optic tract terminate in the lateral geniculate body, some pass through the superior brachium to the superior colliculus, and others either pass over or through the lateral geniculate body to the pulvinar of the thalamus. These end-stations are often called the primary visual centers.
The lateral geniculate body consists of medium-sized pigmented nerve cells arranged in several layers by the penetrating fibers of the optic tract. Their axons pass upward beneath the longer fibers of the optic tract, the taenia semicircularis, the caudate nucleus and the posterior horn of the lateral ventricle where they join the optic radiation of Gratiolet. They
pass backward and medially to terminate in the visuo-sensory cortex in the immediate neighborhood of the calcarine fissure
of the occipital lobe. This center is connected with the one in the opposite side by commissural fibers which course in the
optic radiation and the splenium of the corpus callosum. Association fibers connect it with other regions of the cortex of the
same side.
The region of the pulvinar in which optic tract fibers terminate resembles in structure the lateral geniculate body. Its
axons also have a similar course though in a somewhat more dorsal plane.
The superior colliculus receives fibers from the optic tract through the superior brachium. Some enter by the superficial white layer (stratum zonale), others appear to dip down into the gray cap (stratum cinereum) while others probably
decussate across the midline to the opposite colliculus. Other fibers from the superior brachium pass into the stratum opticum (upper gray-white layer). Some of these turn upward into the gray cap while others terminate among the cells of this
layer. Since the superior colliculi appear to be the central organs concerned in the control of eye-muscle movements and
eye-muscle reflexes we should expect to find them receiving fibers from other sensory paths. Many fibers pass to the superior colliculus from the medial fillet as the latter passes through the tegmentum bringing the superior colliculus into relation
with the sensory fibers of the spinal cord. Fibers from the central sensory path of the trigeminal probably pass with these.
Part of the ventral spinocerebellar tract (Gowers) is said to pass up through the reticular formation of the pons and midbrain toward the superior colliculus and the thalamus. The superior colliculus is intimately connected with the central auditory path (the lateral lemniscus), as part of its fibers pass the inferior colliculus and terminate in the superior colliculus.
They are probably concerned with reflex movements of the eyes depending on auditory stimuli. The superior colliculus is
said to receive fibers from the stria medullaris thalamis of the opposite side which pass through the commissura habenulae
and turn back to the roof of the mid-brain, especially to the superior colliculus. By this path both the primary and cortical
olfactory centers are brought into relation with the eye-muscle reflex apparatus.
The fibers which pass to the nuclei of the eye muscles arise from large cells in the stratum opticum and stratum lemnisci and pass around the ventral aspect of the central gray matter where most of them cross the midline in the fountain decussation of Meynert, and then turn downward to form the ventral longitudinal bundle. This bundle runs down partly
through the red nucleus, in the formatio reticularis, ventral to the posterior longitudinal bundle of the mid-brain, pons and
medulla oblongata into the ventral funiculus of the spinal cord where it is known as the tectospinal fasciculus. Some of the
fibers are said to pass down with the rubrospinal tract in the lateral funiculus. Some fibers do not decussate but pass down
in the ventral longitudinal bundle of the same side on which they arise unless possibly they come from the opposite colliculus over the aqueduct. From the ventral longitudinal bundle collaterals are given off to the nuclei of the eye muscles, the
oculomotor, the trochlear and the abducens. Many collaterals pass to the red nucleus, and are probably concerned with the
reflexes of the rubrospinal tract. The fibers of the tectospinal tract end by collaterals and terminals either directly or indirectly among the motor cells in the anterior column of the spinal cord.
The superior colliculus receives fibers from the visual sensory area of the occipital cortex; they pass in the optic radiation. Probably no fibers pass from the superior colliculus to the visual sensory cortex.
The Olfactory Nerves (I cranial) or nerves of smell arise from spindle-shaped bipolar cells in the surface epithelium of the olfactory region of the nasal cavity. The non-medullated axons pass upward in groups through numerous foramina in the cribriform plate to the olfactory bulb; here several fibers, each ending in a tuft of terminal filaments, come into
relation with the brush-like end of a single dendrite from a mitral cell. This interlacing gives rise to the olfactory glomeruli
of the bulb. The termination of several or many olfactory fibers in a single glomerulus where they form synapses with the
dendrites of one or two mitral cells provides for the summation of stimuli in the mitral cells and accounts in part at least for
the detection by the olfactory organs of very dilute solutions. Lateral arborizations of the dendrites of the mitral cells and
the connection of neighboring glomeruli by the axons of small cells of the glomeruli and the return of impulses of the mitral cells by collaterals either directly or through the interpolation of granule cells to the dendrites of the mitral cells reinforce the discharge of the mitral cells along their axons. The axons turn abruptly backward in the deep fiber layer of the
bulb to form the olfactory tract. The olfactory tract is continued into the olfactory trigone, just in front of the anterior perfo-
rated substance. The axons of the mitral cells on reaching the olfactory trigone separate into three bundles, the lateral olfactory stria, the medial olfactory stria and the less marked intermedial olfactory stria.
The lateral olfactory striae curve lateralward, a few of the fibers end in the olfactory trigone and the antero-lateral
portion of the anterior perforated substance. Most of the fibers, however, pass into the uncus, the anterior end of the hippocampal gyrus, and there end in the complicated cortex of the hippocampal gyri. The lateral striae more or less disappear as
they cross the antero-lateral region of the anterior perforated substance.
The greater mass of the fibers of the olfactory tract pass into the lateral stria. Numerous collaterals are given into the
plexiform layer of the subfrontal cortex, over which the striae pass on their way to the uncus, where they intermingle with
the apical dendrons of the medium-sized and small pyramidal cells of the pyramidal layer of this subfrontal or frontal olfactory cortex. The axons give rise to projection fibers which take an antero-posterior direction to the subthalamic region sending collaterals and terminal branches to the stria medullaris and others toward the thalamus. Some of the fibers extend farther back and are believed to reach the pons and medulla oblongata.
Most of the fibers of the lateral olfactory stria pass to the hippocampal region of the cortex, especially to the gyrus
hippocampi, which may be regarded as the main ending place of the secondary olfactory path derived from axons of the
mitral cells.
The fibers of the medial olfactory striae terminate for the most part in the parolfactory area (Broca’s area), a few
end in the subcallosal gyrus and a few in the anterior perforated substance and the adjoining part of the septum pellucidum.
Some of the fibers pass into the anterior commissure (pars olfactoria) to the olfactory tract of the opposite side where they
end partly within the granular layer and partly in the neighborhood of the glomeruli of the olfactory bulb, thus connecting
the bulbs of the two sides.
The intermediate olfactory striae are as a rule scarcely visible, the fibers terminate in the anterior perforated substance, a few are said to continue to the uncus.
The trigonum olfactorium, anterior perforated substance and the adjoining part of the septum pellucidum are important primary olfactory centers, especially for olfactory reflexes; in these centers terminate many axons from the mitral
cells of the olfactory bulb. In addition the gray substance of the olfactory tract and the gyrus subcallosus receive terminals
of the mitral cells.
The pathways from these centers to lower centers in the brain-stem and spinal cord are only partially known. The
most direct path, the tractus olfactomesencephalicus (basal olfactory bundle of Wallenburg), is supposed to arise from
cells in the gray substance of the olfactory tract, the olfactory trigone, the anterior perforated substance and the adjoining
part of the septum pellucidum. The fibers are said to pass direct to the tuber cinereum, to the corpus mammillare, to the
brainstem and the spinal cord. The fibers which enter the mammillary body probably come into relation with cells whose
axons give rise to the fasciculus mammillo-tegmentalis (mammillo-tegmental bundle of Gudden) which is supposed to
end in the gray substance of the tegmentum and of the aqueduct; some of its fibers are said to join the posterior longitudinal
bundle and others to extend as far as the reticular formation of the pons.
Some of the fibers of the medial olfactory stria came into relation with cells in the parolfactory area of Broca and in
the anterior perforated substance, whose axons course in the medullary stria of the thalamus. As the axons pass through the
lower part of the septum pellucidum they are joined by other fibers whose cells receive impulses from the mitral cells.
These fibers of the medullary stria end for the most part in the habenular nucleus of the same side, some, however, cross in
the habenular commissure (dorsal part of the posterior commissure) to the habenular nucleus of the opposite side. A few
fibers of the medullary stria are said to pass by the habenular nucleus to the roof of the mid-brain, especially the superior
colliculus, while a few others come into relation with the posterior longitudinal bundle and association tracts of the mesencephalon.
The ganglion of the habenulae located in the trigonum habenulae just in front of the superior colliculus contains a
mesial nucleus with small cells and a lateral nucleus with larger cells. The axons of these cells are grouped together in a
bundle, the fasciculus retroflexus of Meynert, which passes ventrally medial to the red nucleus and terminates in a small
medial ganglion in the substantia perforata posterior, immediately in front of the pons, called the interpeduncular ganglion.
The interpeduncular ganglion has rather large nerve cells whose axons curve backward and downward as the tegmental bundle of Gudden, to end partly in the dorsal tegmental nucleus and surrounding gray substance where they come
into relation with association neurons and the dorsal longitudinal bundle of Schütz.
The majority of the axons that arise from the mitral cells of the olfactory bulb and course in the olfactory tract
course in the lateral olfactory stria to the uncus and hippocampal gyrus, and terminate in the cortex. Other fibers probably
pass to the uncus and hippocampal gyrus from the primary olfactory centers in the trigonum and anterior perforated substance. The gyrus hippocampus is continued through the isthmus into the gyrus cinguli which passes over the corpus callosum to the area parolfactoria. The cortical portions of these gyri are connected together by a thick association bundle, the
cingulum, that lies buried in the depth of the gyrus cinguli extending forward to the parolfactory area and backward into
the hippocampal region. The axons from the gyrus cinguli pass into the cingulum, many of them bifurcate, the anterior
branches together with the axons which run in that direction are traceable as far forward as the anterior part of the septum
pellucidum and the anterior end of the corpus striatum, where some of them are incorporated with projection fibers passing
toward the internal capsule. The branches and axons which pass backward terminate partly in the hippocampus, the dentate
gyrus and hippocampal gyrus. Shorter association fibers connect various sections of the gyrus fornicatus (cingulate gyrus,
isthmus, and hippocampal gyrus) and these with other regions of the cortex. These gyri constitute the cortical center for
smell.
The dentate gyrus which may be considered as a modified part of the hippocampus is partially separated from the
gyrus hippocampus by the hippocampal fissure and from the fimbria by the fimbrio-dentate sulcus; it is intimately connect-
ed with the hippocampal gyrus and the hippocampus. When followed backward the dentate gyrus separates from the fimbria at the splenium, loses its incisions and knobs, and as the fasciola cinerea passes over the splenium onto the dorsal surface of the corpus callosum and spreads out into a thin layer of gray substance known as the indusium, which can be traced
forward around the genu of the corpus callosum into the gyrus subcallosus. The white matter of the indusium known as the
medial longitudinal striae (nerves of Lancisi) and the lateral longitudinal striae, are related to the indusium somewhat as
the cingulum is to the gyrus cinguli. Axons from the indusium pass into the longitudinal striae, some running forward and
others backward while some after entering the medial longitudinal stria, pierce the corpus callosum to join the fornix. Some
of the fibers which pass forward extend around the front of the corpus callosum and the anterior commissure, then curve
downward, according to Cajal, to enter the corpus striatum where they join the olfactory projection-path. Other fibers are
said to arise in the parolfactory area, the gyrus subcallosus and the anterior perforated substance (diagonal band of Broca) and course backward in the longitudinal striae to the dentate gyrus and the hippocampal region. The indusium is usually
considered as a rudimentary part of the rhinencephalon.
The olfactory projection fibers which arise from the pyramid cells of the uncus and hippocampus and from the
polymorphic cells of the dentate gyrus form a dense stratum on the ventricular surface, especially on the hippocampus,
called the alveus. These fibers pass over into the fimbria and are continued into the fornix. About one-fourth of all the fibers of the fimbria are large projection fibers, the other three-fourths consist of fine commissural fibers which pass from the
hippocampus of one side through the fimbria and hippocampal commissure (ventral psalterium or lyre), to the fimbria
and hippocampus of the opposite side where they penetrate the pyramidal layer and terminate in the stratum radiatum. The
fibers which course in the fornix pass forward and downward into the corpora mammillare where numerous collaterals are
given off and a few terminate. Most of the fibers in the fornix, however, pass through the corpora, cross the middle line and
turn downward in the reticular formation in which they are said to be traceable as far as the pons and possibly farther. As
the fornix passes beneath the corpus callosum it receives fibers from the longitudinal striae of the indusium and from the
cingulum; these are the perforating fibers of the fornix which pass through the corpus callosum and course in the fornix
toward the mammillary body. As the fornix passes the anterior end of the thalamus a few fibers are given off to the stria
medullaris of the thalamus and turn back in the stria to the habenular ganglion of the same and the opposite side, having
probably the same relation that the reflex fibers have which arise from the primary centers and course in the stria medullaries of the thalamus. Aside from the fibers of the fornix which pass through the mammillary body to decussate and descend
(as the mammillo-mesencephalic fasciculus), many fibers are said to pass into the bundle of Vicq d’Azyr, and one bundle
of fibers is said to pass from the fornix to the tuber cinereum.
The mammillary bodies receive collaterals and terminals then from the cortical centers via the fornix and probably
other collaterals and terminals are received directly from the primary centers through the tractus olfactomesencephalicus.
According to Cajal fibers also reach the mammillary body through the peduncle of the corpus mammillare from the arcuate
fibers of the tegmentum and from the main fillet. The fornix probably brings the cortical centers into relation with the reflex path that runs from the primary centers to the mammillary body and the tuber cinereum.
The bundle of Vicq d’Azyr (mammillo-thalamic fasciculus) arises from cells in both the medial and lateral nuclei
of the mammillary body and by fibers that are directly continued from the fornix. There axons divide within the gray matter; the coarser branches pass into the anterior nucleus of the thalamus as the bundle of Vicq d’Azyr, the finer branches pass
downward as the mammillo-tegmental bundle of Gudden. The bundle of Vicq d’Azyr spreads out fan-like as it terminates
in the anterior or dorsal nucleus of the thalamus. A few of the fibers pass through the dorsal nucleus to the angular nucleus
of the thalamus. The axons from these nuclei are supposed to form part of the thalamocortical system.
The mammillo-tegmental bundle has already been considered under the olfactory reflex paths.
The amygdaloid nucleus and the taenia semicircularis (stria terminalis) probably belong to the central olfactory
apparatus. The taenia semicircularis extends from the region of the anterior perforated substance to the nucleus amygdalae.
Its anterior connections are not clearly understood. Fibers are said to arise from cells in the anterior perforated substance;
some of the fibers pass in front of the anterior commissure, others join the fornix for a short distance as they pass behind
the anterior commissure. The two strands ultimately join to form the taenia and pass backward in the groove between the
caudate nucleus and the thalamus to the amygdaloid nucleus. Other fibers are said to pass in the opposite direction from the
amygdaloid nucleus to the thalamus.
Practice skills
Students are supposed to identify the following structures on the samples:
Self-taught class 9. Parasympathetic supplement of the head and neck.
The aim: to learn the parasympathetic supplement of head and heck.
Professional orientation: the knowledge of this topic is necessary for doctors of all specialities; it represents special interest for therapists, neurologists, neuropathologists and others.
The plan of the self-taught class:
A. Revise the division of the parasympathetic nervous system into the cranial and pelvic parts.
B. Learn the structures composing the cranial part of the parasympathetic nervous system.
C. Learn the parasympathetic part of the oculomotor nerve – the accessory oculomotor nucleus – and the
course of fibers arising from it.
D. Learn the composition and topography of the ciliary ganglion. Find out the organs innervated from the ciliary ganglion and the course of its fibers to these organs.
E. Learn the parasympathetic part of the facial nerve – the superior salivatory nucleus – and the course of fi-
bers arising from it.
F. Learn the composition and topography of the pterygopalatine, submandibular and sublingual ganglia. Find
out the organs innervated from these ganglia and the course of the fibers from the ganglia to these organs.
G. Learn the parasympathetic part of the glossopharyngeal nerve – the inferior salivatory nucleus – and the
course of fibers arising from it.
H. Learn the composition and topography of the otic ganglion. Find out the organ innervated from the otic
ganglion and the course of its fibers to this organ.
I. Learn the parasympathetic part of the vagus nerve – the dorsal nucleus – and the course of fibers arising
from it. Find out the organs of head and neck, innervated by the vagus nerve.
For more information see the practice classes 8 (Review of cranial nerves. I, II, ІІІ, ІV, VI, ХІ, ХІІ pairs
of cranial nerves), 10 (The facial nerve (VIІ). The glossopharyngeal (ІХ) nerve), 11 (The vagus nerve (Х). The
parasympathetic nervous system) and self-taught class 8 (Review of the peripheral nervous system. Review of
cranial nerves).
Self-taught class 10. Sympathetic supplement of the head and neck.
The aim: to learn the sympathetic supplement of head and heck.
Professional orientation: the knowledge of this topic is necessary for doctors of all specialities; it represents special interest for therapists, neurologists, neuropathologists and others.
The plan of the self-taught class:
A. Revise the structure of the sympathetic nervous system, the localization of its centers and ganglia.
B. Find out which sympathetic ganglia send fibers to the organs of head and neck.
C. Learn the cervical portion of the sympathetic system.
D. Learn the cephalic portion of the sympathetic system.
The Cervical Portion of the Sympathetic System
(Pars Cervicalis S. Sympathici)
The cervical portion of the sympathetic trunk consists of three ganglia, distinguished, according to their positions,
as the superior, middle, and inferior ganglia, connected by intervening cords. This portion receives no white rami communicantes from the cervical spinal nerves; its spinal fibers are derived from the white rami of the upper thoracic nerves,
and enter the corresponding thoracic ganglia of the sympathetic trunk, through which they ascend into the neck.
The superior cervical ganglion (ganglion cervicale superius), the largest of the three, is placed opposite the second
and third cervical vertebrae. It is of a reddishgray color, and usually fusiform in shape; sometimes broad and flattened, and
occasionally constricted at intervals; it is believed to be formed by the coalescence of four ganglia, corresponding to the
upper four cervical nerves. It is in relation, in front, with the sheath of the internal carotid artery and internal jugular vein;
behind, with the Longus capitis muscle.
Its branches may be divided into inferior, lateral, medial, and anterior.
The Inferior Branch communicates with the middle cervical ganglion.
The Lateral Branches (external branches) consist of gray rami communicantes to the upper four cervical nerves
and to certain of the cranial nerves. Sometimes the branch to the fourth cervical nerve may come from the trunk connecting
the upper and middle cervical ganglia. The branches to the cranial nerves consist of delicate filaments, which run to the
ganglion nodosum of the vagus, and to the hypoglossal nerve. A filament, the jugular nerve, passes upward to the base of
the skull, and divides to join the petrous ganglion of the glossopharyngeal, and the jugular ganglion of the vagus.
The Medial Branches (internal branches) are peripheral, and are the larnygopharyngeal branches and the superior cardiac nerve.
The laryngopharyngeal branches (rami laryngopharyngei) pass to the side of the pharynx, where they join with
branches from the glossopharyngeal, vagus, and external laryngeal nerves to form the pharyngeal plexus.
The superior cardiac nerve (n. cardiacus superior) arises by two or more branches from the superior cervical ganglion, and occasionally receives a filament from the trunk between the first and second cervical ganglia. It runs down the
neck behind the common carotid artery, and in front of the Longus colli muscle; and crosses in front of the inferior thyroid
artery, and recurrent nerve. The course of the nerves on the two sides then differ. The right nerve, at the root of the neck,
passes either in front of or behind the subclavian artery, and along the innominate artery to the back of the arch of the aorta,
where it joins the deep part of the cardiac plexus. It is connected with other branches of the sympathetic; about the middle
of the neck it receives filaments from the external laryngeal nerve; lower down, one or two twigs from the vagus; and as it
enters the thorax it is joined by a filament from the recurrent nerve. Filaments from the nerve communicate with the thyroid
branches from the middle cervical ganglion. The left nerve, in the thorax, runs in front of the left common carotid artery
and across the left side of the arch of the aorta, to the superficial part of the cardiac plexus.
The Anterior Branches (nn. carotici externi) ramify upon the common carotid artery and upon the external carotid
artery and its branches, forming around each a delicate plexus, on the nerves composing which small ganglia are occasionally found. The plexuses accompanying some of these arteries have important communications with other nerves. That surrounding the external maxillary artery communicates with the submaxillary ganglion by a filament; and that accompanying
the middle meningeal artery sends an offset to the otic ganglion, and a second, the external petrosal nerve, to the genicular ganglion of the facial nerve.
The middle cervical ganglion (ganglion cervicale medium) is the smallest of the three cervical ganglia, and is occasionally wanting. It is placed opposite the sixth cervical vertebra, usually in front of, or close to, the inferior thyroid artery.
It is probably formed by the coalescence of two ganglia corresponding to the fifth and sixth cervical nerves.
It sends gray rami communicantes to the fifth and sixth cervical nerves, and gives off the middle cardiac nerve.
The Middle Cardiac Nerve (n. cardiacus medius; great cardiac nerve), the largest of the three cardiac nerves, arises from the middle cervical ganglion, or from the trunk between the middle and inferior ganglia. On the right side it descends behind the common carotid artery, and at the root of the neck runs either in front of or behind the subclavian artery;
it then descends on the trachea, receives a few filaments from the recurrent nerve, and joins the right half of the deep part of
the cardiac plexus. In the neck, it communicates with the superior cardiac and recurrent nerves. On the left side, the middle
cardiac nerve enters the chest between the left carotid and subclavian arteries, and joins the left half of the deep part of the
cardiac plexus.
The inferior cervical ganglion (ganglion cervicale inferius) is situated between the base of the transverse process
of the last cervical vertebra and the neck of the first rib, on the medial side of the costocervical artery. Its form is irregular;
it is larger in size than the preceding, and is frequently fused with the first thoracic ganglion. It is probably formed by the
coalescence of two ganglia which correspond to the seventh and eighth cervical nerves. It is connected to the middle cervical ganglion by two or more cords, one of which forms a loop around the subclavian artery and supplies offsets to it. This
loop is named the ansa subclavia (Vieussenii).
The ganglion sends gray rami communicantes to the seventh and eighth cervical nerves.
It gives off the inferior cardiac nerve, and offsets to bloodvessels.
The inferior cardiac nerve (n. cardiacus inferior) arises from either the inferior cervical or the first thoracic ganglion. It descends behind the subclavian artery and along the front of the trachea, to join the deep part of the cardiac plexus.
It communicates freely behind the subclavian artery with the recurrent nerve and the middle cardiac nerve.
The offsets to bloodvessels form plexuses on the subclavian artery and its branches. The plexus on the vertebral artery is continued on to the basilar, posterior cerebral, and cerebellar arteries. The plexus on the inferior thyroid artery accompanies the artery to the thyroid gland, and communicates with the recurrent and external laryngeal nerves, with the superior cardiac nerve, and with the plexus on the common carotid artery.
The Cephalic Portion of the Sympathetic System (Pars Cephalica S. Sympathici)
The cephalic portion of the sympathetic system begins as the internal carotid nerve, which appears to be a direct
prolongation of the superior cervical ganglion. It is soft in texture, and of a reddish color. It ascends by the side of the internal carotid artery, and, entering the carotid canal in the temporal bone, divides into two branches, which lie one on the lateral and the other on the medial side of that vessel.
The lateral branch, the larger of the two, distributes filaments to the internal carotid artery, and forms the internal
carotid plexus.
The medial branch also distributes filaments to the internal carotid artery, and, continuing onward, forms the cavernous plexus.
The internal carotid plexus (plexus caroticus internus; carotid plexus) is situated on the lateral side of the internal
carotid artery, and in the plexus there occasionally exists a small gangliform swelling, the carotid ganglion, on the under
surface of the artery. The internal carotid plexus communicates with the semilunar ganglion, the abducent nerve, and the
sphenopalatine ganglion; it distributes filaments to the wall of the carotid artery, and also communicates with the tympanic
branch of the glossopharyngeal nerve.
The communicating branches with the abducent nerve consist of one or two filaments which join that nerve as it lies
upon the lateral side of the internal carotid artery. The communication with the sphenopalatine ganglion is effected by a
branch, the deep petrosal, given off from the plexus on the lateral side of the artery; this branch passes through the cartilage filling up the foramen lacerum, and joins the greater superficial petrosal to form the nerve of the pterygoid canal (Vidian nerve), which passes through the pterygoid canal to the sphenopalatine ganglion. The communication with the tympanic
branch of the glossopharyngeal nerve is effected by the caroticotympanic, which may consist of two or three delicate filaments.
The cavernous plexus (plexus cavernosus) is situated below and medial to that part of the internal carotid artery
which is placed by the side of the sella turcica in the cavernous sinus, and is formed chiefly by the medial division of the
internal carotid nerve. It communicates with the oculomotor, the trochlear, the ophthalmic and the abducent nerves, and
with the ciliary ganglion, and distributes filaments to the wall of the internal carotid artery. The branch of communication
with the oculomotor nerve joins that nerve at its point of division; the branch to the trochlear nerve joins it as it lies on the
lateral wall of the cavernous sinus; other filaments are connected with the under surface of the ophthalmic nerve; and a second filament joins the abducent nerve.
The filaments of connection with the ciliary ganglion arise from the anterior part of the cavernous plexus and enter
the orbit through the superior orbital fissure; they may join the nasociliary branch of the ophthalmic nerve, or be continued
forward as a separate branch.
The terminal filaments from the internal carotid and cavernous plexuses are prolonged as plexuses around the anterior and middle cerebral arteries and the ophthalmic artery; along the former vessels, they may be traced to the pia mater;
along the latter, into the orbit, where they accompany each of the branches of the vessel. The filaments prolonged on to the
anterior communicating artery connect the sympathetic nerves of the right and left sides.
Written tests of cranial nerves
I. Tests of basic theory
1. Nerve fibers belonging to which cranial
nerve(s) are found in the pterygopalatine fossa?
A. CN V
B. CN VII
C. CN IX
D. a and b
E. *a, b and c
2. The mucosa covering most of the lingual tonsil
would have sensory innervation by neurons
whose cell bodies are in the
A. geniculate ganglion
B. *glossopharyngeal ganglion
C. submandibular ganglion
D. trigeminal ganglion
E. vagal ganglion
3. Which of the following statements is/are
TRUE?
A. *the hypoglossal nerve passes lateral to the
internal and external carotid arteries
B. the hypoglossal nerve passes superior, lateral, inferior and medial to the submandibular duct
C. sensory innervation to the tongue travels in
the hypoglossal nerve
D. a and b
E. a and c
4. The gag reflex involves pharyngeal stimulation
followed by contraction of the pharyngeal constrictors. A successful reflex requires functioning
A. glossopharyngeal nerves
B. vagus nerves
C. *both
D. neither
5. Touching the upper eyelid or the corneal caused
a blink reflex, but touching the lower eyelid did
not. The problem is non-function of the
A. entire ophthalmic nerve
B. entire trigeminal nerve
C. frontal nerve
D. *infraorbital nerve
E. nasociliary nerve
6. The temporomandibular joint syndrome is
characterized by pain from the joint. The cell
bodies of the pain fibers are in the:
A. geniculate ganglion
B. glossopharyngeal ganglion
C. vagus ganglion
D. otic ganglion
E. *trigeminal ganglion
7. The facial nerve:
A. *exits the skull through the stylomastoid
foramen
B. divides into three major trunks in the parotid gland
C. supplies the parotid gland with parasympathetic fibers
8.
9.
10.
11.
12.
13.
D. a and b
E. None of the above are true concerning the
facial nerve
Pain from swelling of the parotid gland, as in a
case of mumps, is transmitted towards the central nervous system in which nerve?
A. lesser occipital
B. ascending branch of transverse cervical
C. descending branch of transverse cervical
D. temporal branch of facial
E. *auriculotemporal
All the following are true for the trigeminal
nerve EXCEPT:
A. *it supplies motor innervation to the buccinator muscle
B. it supplies general sense to the conjunctiva
in the orbit
C. it supplies general sense to the mucosa of
the mouth
D. it supplies general sense to the nasal mucosa
E. it supplies general sense to the skin of the
face
During surgery of the right neck the accessory
nerve was cut. The ends were brought together
and sutured. The surgery was completed. What
signs and symptoms would be expected to be
observed following the surgery but prior to regeneration of the nerve?
A. difficulty in elevating the right shoulder
B. difficulty in abduction of the right arm
C. difficulty in turning the head to the left
D. a and c
E. *a, b, and c
To reach the intrinsic muscles of the larynx,
their major nerve pierces the
A. conus elasticus
B. cricotracheal membrane
C. *quadrangular membrane
D. thyrohyoid membrane
E. none of the above
Cell bodies of preganglionic fibers in the pterygoid canal are located in the
A. geniculate ganglion
B. pterygopalatine ganglion
C. superior cervical ganglion
D. *superior salivatory nucleus
E. c and d
An infection in the sublingual gland spreads to
form an abscess around the gland beside the
tongue. The nerve/s exposed to the abscess
would be the:
A. Glossopharyngeal
B. Hypoglossal
C. Lingual
D. *b and c
E. a, b and c
14. The pharyngeal plexus innervates all of the following EXCEPT:
A. pharyngeal constrictors
B. *stylopharyngeus muscle
C. palatopharyngeus muscle
D. salpingopharyngeus muscle
E. palatoglossus muscle
15. The nasociliary nerve:
A. is a branch of the maxillary nerve
B. *is made up of sensory fibers
C. gives rise to the supratrochlear and supraorbital nerves
D. its branches remain in the orbit
E. all of the above
16. An acoustic neuroma (a space occupying tumor) in the internal acoustic meatus can produce all of the following symptoms EXCEPT:
A. decrease in salivation
B. *increased lacrimation
C. loss of hearing
D. loss of taste to the anterior two-thirds of the
tongue
E. paralysis of the buccinator muscle
17. The chorda tympani nerve:
A. is a branch of the facial nerve
B. traverses through the middle ear
C. contains parasympathetic and somatic motor fibers
D. *a and b
E. b and c
18. A patient had his mouth opened too wide while
having a breathing tube inserted, causing the
posterior part of the temporomandibular joint
capsule to be tom. When he awakes, he will be
conscious of pain impulses traveling in the:
A. *auriculotemporal nerve
B. buccal nerve
C. inferior alveolar nerve
D. nerve to the masseter muscle
E. nerve to the medial pterygoid muscle
19. A deep vertical slash on the face extending
from the zygomatic arch to the mid point of the
inferior border of the mandible could result in:
A. loss of ability to close the ipsilateral eye
B. a severed parotid duct
C. loss of taste over the anterior two-thirds of
the tongue
D. *a and b
E. a, b, and c
20. A hard slap to the eye causes a "blow out" fracture of the floor of the orbit If the nerve traveling in the floor is severed, there will be sensory
loss to all the following EXCEPT:
A. ala of the nose
B. lower eyelid
C. *tip of the nose
D. upper lip
E. all of the above
21. The recurrent (or inferior) laryngeal nerve innervates all the intrinsic laryngeal muscles,
EXCEPT:
A. lateral cricoarytenoid
B. posterior cricoarytenoid
C. cricothyroid
D. vocalis
E. aryepiglottis
22. The submandibular ganglion contains preganglionic parasympathetic axons from cranial
nerve:
A. III
B. V
C. VII
D. IX
E. X
23. A lesion of the facial nerve at its exit from the
skull would result in:
A. an ipsilateral loss of taste to the anterior
tongue
B. a decrease in saliva delivered directly onto
the floor of the mouth
C. a sensory loss to the tongue
D. all of the above
E. none of the above
24. The oculomotor nerve supplies motor innervation to all the following muscles, EXCEPT:
A. levator palpebrae superioris
B. orbicularis oculi
C. superior rectus
D. medial rectus
E. inferior oblique
25. The parasympathetic nervous system has origin
in all the following cranial nerves, EXCEPT:
A. oculumotor
B. facial
C. glossopharyngeal
D. vagus
E. trigeminal
26. The following statements concerning the facial
nerve or its named branches are true, EXCEPT:
A. The ganglion of the facial nerve is the geniculate ganglion.
B. The buccinator muscle is innervated by a
branch of the facial nerve.
C. The greater petrosal N. is joined by a postganglionic sympathetic nerve.
D. Salivary glands are innervated by parasympathetic fibers of the facial nerve.
E. The anterior and posterior bellies of the digastric are innervated by branches of the
facial nerve.
27. The motor division of the trigeminal nerve
leaves the skull through the:
A. Foramen rotundum
B. Foramen ovale
C. Superior orbital fissure
D. Inferior orbital fissure
E. Foramen spinosum
28. Pick the discordant pair:
A. optic canal : optic nerve
B. foramen ovale: mandibular division of the
trigeminal nerve
C. jugular foramen : glossopharyngeal nerve
D. superior orbital fissure : oculomotor n.
E. internal acoustic meatus : abducens n.
29. The right recurrent laryngeal nerve usually
loops around which of the following structures:
A. aortic arch
B. axillary A
C. ligamentum arteriosum
D. subclavian A
E. ansa cervicalis
30. The nerve of the pterygoid canal contains:
A. preganglionic parasympathetic fibers from
CNVII.
B. postganglionic parasympathetic fibers from
CNVII.
C. special sensory fibers from CNVII
D. preganglionic sympathetic fibers
E. none of the above
31. "Branches of the CNV include all of the following, EXCEPT:"
A. lesser petrosal
B. zygomatic
C. frontal
D. ethmoidal
E. lacrimal
"Each group of questions below consists of
lettered headings followed by a list of numbered
word or phrase, select the one heading that is most
closely related to it. A particular answer may be
used once, more than once or not at all."
(a) stylomastoid foramen
(b) jugular foramen
(c) superior orbital fissure
(d) carotid canal
(e) foramen rotundum
32. a b c d e --maxillary nerve
33. a b c d e --trochlear nerve
34. a b c d e --postganglionic sympathetics
35. a b c d e --facial nerve
36. a b c d e --glossopharyngeal nerve
37.
Matching Type
(a) cranial nerve II
(b) cranial nerve V
(c) cranial nerve VI
(d) cranial nerve VII
(e) cranial nerve XI
38. a b c d e --longest cranial nerve running in bone
39. a b c d e --has extra-cranial components
40. a b c d e --largest nerve seen in the skull
41. a b c d e --special sensory only
42. a b c d e --most sensitive to increased intracranial pressure
43. Which of the following is a branch of the maxillary division of the trigeminal nerve?
A. nasociliary N.
B. mental N.
C. lacrimal N.
D. infraorbital N.
E. chorda tympana N.
44. Ptosis of the eyelid may be caused by injury to
the:
A. nerve to the levator palpebrae superioris M.
B. abducens N.
C. superior oblique M.
D. superior rectus M.
E. facial N.
II. Tests from “Step-1” database (with explanation)
1. A physician is performing a cranial nerve examination on a patient. While testing the gag reflex, it is noted that when the right side of the
pharyngeal mucosa is touched, the patient's
uvula deviates to the right. When the left side of
the pharyngeal mucosa is touched, the patient
does not gag. Which of the following is the
most likely location of his lesion?
A. Left glossopharyngeal nerve and left vagus
nerve
B. Left glossopharyngeal nerve only
C. Left vagus nerve only
D. Right glossopharyngeal nerve and right vagus nerve
E. Right glossopharyngeal nerve only
F. Right vagus nerve only
Explanation:
The correct answer is A. The gag reflex requires the
glossopharyngeal nerve for the sensory limb of the
reflex (unilateral) and the vagus nerve for the motor
limb of the reflex (bilateral). A lesion of the left
glossopharyngeal nerve will denervate the sensory
receptors on the left side of the pharynx. Thus when
the left side is touched, the patient does not feel it
and does not gag. The gag reflex requires the vagus
nerve for the motor limb of the reflex. If the left
vagus nerve is lesioned, the left side of the soft palate will not elevate during a gag and the uvula will
deviate to the right. In this case, the patient only
feels the touch on the right side and only elevates
the right side of the palate. Thus there is a lesion of
both the left glossopharyngeal nerve and the left
vagus nerve.
If the patient had a lesion of the left glossopharyngeal nerve only (choice B), there would have been
no gag when the left side is touched but there would
be a normal gag, without deviation of the uvula,
when the right side was touched.
If the patient had a lesion of the left vagus nerve
only (choice C), the patient would have deviation of
the uvula to the right when a gag was elicited, but
touching either side of the pharynx would elicit a
gag.
If the patient had a lesion of the right glossopharyngeal nerve and the right vagus nerve (choice D),
touching the right side of the pharynx would not
elicit a gag and touching the left side of the pharynx
would elicit a gag with the uvula deviating to the
left.
If the patient had a lesion of the right glossopharyngeal nerve only (choice E), there would be no gag
when the right side is touched but there would be a
normal gag, without deviation of the uvula, when
the left side was touched.
If the patient had a lesion of the right vagus nerve
only (choice F), the patient would have deviation of
the uvula to the left when a gag was elicited and
touching either side of the pharynx would elicit a
gag.
2. A patient's left hypoglossal nerve (CN XII) is
injured during a carotid endarterectomy. Which
of the following would most likely result from
this injury?
A. Decreased gag reflex on the left
B. Decreased salivation from the left submandibular and sublingual salivary glands
C. Deviation of the tongue to the left on protrusion
D. Inability to elevate the pharynx on the left
during swallowing
E. Inability to perceive sweet and salt taste
sensation on the anterior part of the left side
of the tongue
Explanation:
The correct answer is C. The hypoglossal nerve is a
pure motor nerve (general somatic efferent) to the
intrinsic muscles of the tongue. If the nerve is damaged, denervation atrophy of the affected side will
permit the intact musculature of the opposite side to
operate unopposed, thereby protruding the tongue
to the side of the injury.
The gag reflex (choice A) is mediated by the glossopharyngeal nerve (CN IX; afferent limb) and the
vagus nerve (CN X; efferent limb).
Choice B is incorrect because the preganglionic
parasympathetic fibers that regulate these two salivary glands are carried by the chorda tympani
(which joins with the lingual nerve) to the submandibular ganglion. Postganglionic fibers are then distributed to these glands.
The muscles responsible for elevation of the pharynx (choice D) are innervated primarily by the vagus nerve (CN X).
Choice E is incorrect because taste fibers for the
anterior two-thirds of the tongue are carried via the
chorda tympani to the facial nerve (CN VII) and
hence to the brainstem.
3. A patient develops an excruciatingly painful
infection of the anterior half of the external ear
canal. Which of the following nerves transmits
this impulse?
A. Auricular branch of the vagus
B. Auriculotemporal nerve
C. Greater auricular nerve
D. Lesser occipital nerve
E. Vestibulocochlear nerve
Explanation:
The correct answer is B. The ear has a complex
sensory nerve supply, which includes all of the
nerves listed. A consequence of this complexity is
that pain actually originating in other sites (teeth
and sinuses are notorious) may be misinterpreted as
ear pain or (less commonly) pain originating in the
ear may be misinterpreted as arising from other
sites. The anterior half of the external ear canal is
supplied by the auriculotemporal nerve, which also
supplies the facial surface of the upper part of the
auricle.
The auricular branch of the vagus (choice A) supplies the posterior half of the external ear canal.
The greater auricular nerve (choice C) supplies both
surfaces of the lower part of the auricle.
The lesser occipital nerve (choice D) supplies the
cranial surface of the upper part of the auricle.
The vestibulocochlear nerve (choice E) supplies
hearing and motion sense.
4. A 55-year-old male mechanic suffers a stroke
while trying to replace a flat tire on the road. He
has a history of hypertension, but had not been
taking his medications regularly. In addition, he
is a heavy smoker, and drinks a six-pack of beer
every weekend. On examination, he is conscious and has difficulty speaking clearly. A
right upper motor neuron paralysis of the facial
nerve is noted; the other cranial nerves are
normal. He has a dense hemiplegia on the right
side, with equal paralysis of the arm and leg.
His lesion most likely involves the
A. convexity of the left frontal lobe
B. convexity of the right frontal lobe
C. corticospinal tract in the upper cervical spinal cord
D. left internal capsule
E. right internal capsule
Explanation:
The correct answer is D. This patient has sustained
a hemorrhage of the left internal capsule secondary
to uncontrolled hypertension. The internal capsule
receives its blood supply from the lenticulostriate
arteries, which are prone to rupture in uncontrolled
hypertension. The anterior limb of the internal capsule conveys frontopontine fibers, the genu conducts corticobulbar fibers, and the posterior limb of
the internal capsule conveys corticospinal fibers to
the contralateral arm and leg. Hemorrhage of the
left internal capsule results in right-sided dense
hemiplegia in which paralysis of the arm and leg
are of the same intensity.
The convexity of the frontal lobe (choices A and B)
does not control the leg. This is done by the medial
aspect of the cerebral hemisphere. Also, a hemorrhage involving the right frontal lobe (choice B)
would affect the left side of the body. This patient
has right-sided paralysis.
Lesions of the corticospinal tract in the upper cervical spinal cord (choice C) would result in hemi- or
quadriparesis/plegia. The cranial nerves would not
be involved.
Hemorrhage involving the right internal capsule
(choice E) would result in left-sided paralysis.
5. A 22-year-old woman presents to her physician
with amenorrhea, weight loss, anxiety, tremor,
heat intolerance and palpitations. Laboratory
examination is consistent with hyperthyroidism,
and the physician prescribes propylthiouracil.
The patient's response to propylthiouracil is
disappointing, and the symptoms recur, then
worsen. Subtotal thyroidectomy is successfully
performed, but following the surgery, the woman is extremely hoarse, and can barely speak
above a whisper. This hoarseness is most probably related to damage to a branch which of the
following cranial nerves?
A. Facial
B. Glossopharyngeal
C. Hypoglossal
D. Trigeminal
E. Vagus
Explanation:
The correct answer is E. The recurrent laryngeal
nerves are branches of the vagus (CN X), and supply all intrinsic muscles of the larynx except the
cricothyroid. The right recurrent laryngeal nerve
recurs around the right subclavian artery. The left
recurrent laryngeal nerve recurs in the thorax
around the arch of the aorta and ligamentum arteriosum. Both nerves ascend to the larynx by passing
between the trachea and esophagus, in close proximity to the thyroid gland. The recurrent laryngeal
nerves are therefore particularly vulnerable during
thyroid surgery, and damage may cause extreme
hoarseness.
The facial nerve (choice A) innervates the muscles
of facial expression, the stapedius muscle, and the
lacrimal, submandibular and sublingual glands. It
also mediates taste sensation from the anterior twothirds of the tongue.
The glossopharyngeal nerve (choice B) innervates
the stylopharyngeus muscle and the parotid gland.
Visceral afferents supply the carotid sinus baroreceptors and carotid body chemoreceptors, and mediate taste from the posterior one-third of the
tongue. Somatosensory fibers supply pain, temperature, and touch information from the posterior onethird of the tongue, upper pharynx, middle ear, and
eustachian tube.
The hypoglossal nerve (choice C) innervates the
intrinsic muscles of the tongue, the genioglossus,
hypoglossus, and styloglossus muscles.
The trigeminal nerve (choice D) receives sensory
information from the face and also innervates the
muscles of mastication.
6. A 12-year-old is seen by a pediatrician for a
severe sore throat. Physical examination reveals
a brightly erythematous patch in the upper posterior pharynx. Which of the following cranial
nerves would most likely carry the pain sensation associated with this lesion?
A. III
B. V
C. VII
D. IX
E. X
Explanation:
The correct answer is D. The glossopharyngeal
nerve (IX) carries general somatic sensation from
the posterior part of the upper pharynx, eustachian
tube, and posterior one-third of the tongue. It also
carries taste sensation from the posterior one-third
of the tongue, and conveys afferent fibers from the
carotid sinus baroreceptors and carotid body chemoreceptors, and efferent fibers to the stylopharyngeus muscle.
The oculomotor nerve (III, choice A) supplies the
extraocular muscles (superior, inferior, and medial
recti, and inferior oblique) and levator palpebrae
superioris muscle, and sends parasympathetic fibers
to the ciliary muscle and iris.
The trigeminal nerve (V, choice B) receives somatic
sensation information from the face, lips, gums,
teeth, palate, and anterior two-thirds of the tongue.
The facial nerve (VII, choice C) carries taste sensation from the anterior two-thirds of the tongue. It
supplies motor innervation to the muscles of facial
expression and to the stapedius muscle, and sends
parasympathetic fibers to the lacrimal, submandibular, and sublingual glands.
The vagus nerve (X, choice E) carries sensation
from the lower part of the posterior pharynx, larynx, trachea, and esophagus. It supplies parasympathetic innervation to the thoracic and abdominal
viscera to the left colic flexure.
7. As part of a complete neurological examination,
a medical student takes a cotton-tipped applicator and touches the patient's left eye with a thin
wisp of cotton as the patient looks to the right.
The patient closes both of his eyelids in response. Which of the following cranial nerves
is responsible for the motor limb of this reflex?
A. Abducens
B. Facial
C. Optic
D. Trigeminal
E. Trochlear
Explanation:
The correct answer is B. The corneal reflex is tested
by touching the cornea of one eye with a cotton
wisp; this causes both eyes to close. The afferent, or
sensory, component of the corneal reflex is mediated by the ophthalmic division of the ipsilateral trigeminal nerve (V-1). The efferent, or motor, component is mediated by the facial nerve (CN VII),
bilaterally.
The abducens nerve (CN VI; choice A) innervates
the lateral rectus muscles, which abduct the eyes.
The optic nerve (CN II; choice C) is responsible for
vision, providing the afferent limb of the pupillary
light reflex.
The trigeminal nerve (CN V; choice D) is responsible for the afferent limb of the corneal reflex. It also
innervates the muscles of mastication and provides
sensory innervation to the face.
The trochlear nerve (CN IV; choice E) innervates
the superior oblique muscles, which depress, intort,
and abduct the eyes.
III. Tests from “Krok-1” database
1. A 54-year-old man was admitted to a neurosurgery department with complaints of skin sensitivity absence of the inferior eyelid, lateral surface of the nose, upper lip. During examination
the doctor determined the inflammation of the
second branch of the trigeminal nerve. Through
what cranial foramen does this branch come
out?
A. Spinal.
B. Lacerated.
C. Oval.
D. *Round.
E. Superior orbital fissure.
2. A man of 45 appealed to a clinic complaining
of sensitivity loss in the back third of the
tongue. The function of which pair of crainal
nerves was affected?
A. VIII.
B. X.
C. *IX
D. V
E. XII.
3. Which nerve is damaged, if the right nasolabial
fold is smoothed, right orbital fissure is dilated
(it cannot be screwed up because eyelids don't
close), difficulties arouse while talking and eating (food sticks between the cheek and teeth)?
A. N. trigeminus dexter.
B. N. abducens dexter.
C. N. glossopharyngeus sinister.
D. N. vagus dexter.
E. *N. facialis dexter.
4. After a cranial trauma with the damage of the
superior wall of the right eyesocket a patient
lost the possibility to lift up the upper eyelid of
the right eye and look up. Which nerve was
damaged?
A. N. ophtalmicus.
B. R. inferior n. oculomotorius.
C. N. trochlearis.
D. N. abducens.
E. *R. superior n. oculomotorius.
5. A patient with aneurism of the right subclavian
artery has a husky voice. Irritation of which
nerve can it be connected with?
A. N. laryngeus superior dexter.
B. *N. laryngeus recurrens dexter.
C. N. laryngeus recurrens sinister.
D. N. laryngeus superior sinister.
E. N. laryngeus inferior sinister.
6. A patient was admitted to a neurological department with deflection of the tongue to the
side when extruded, atrophic changes of the
half of the tongue, logopathy, deglutitive problem. Which nerve was damaged?
A. Vagus.
B. Lingual.
C. Chorda tympani.
D. Glossopharyngeal.
E. *Hypoglossal.
7. A patient can not lift an eyebrow on one half of
his face, close eyelids, and bare his teeth.
Which nerve is injured?
A. Maxillary.
B. Ophthalmic.
C. *Facial.
D. Mandibular.
E. Oculomotor.
8. A 60-year-old patient has difficulties forming
and moving a bolus. The tongue is immovable,
logopathy is observed. Which nerve has been
injured?
A. *Sublingual.
B. Accessory.
C. Glossopharyngeal.
D. Trigeminal.
E. Facial.
9. After a cold a patient had incomplete eyeball
abduction. Which nerve was injured?
A. Facial.
B. Glossopharyngeal.
C. Trochlear.
D. Optic.
E. *Abducent.
10. A patient has a tongue motor function disorder.
Which nerve was injured?
A. Accessory.
B. Vagus.
C. Glossopharyngeal.
D. Facial.
E. *Hypoglossal.
11. After a cold a patient had disorder of pain and
temperature sensitivity of anterior 2/3 of the
tongue. Which nerve was injured?
A. Sublingual.
B. *Trigeminal.
C. Phrenic.
D. Vagus.
E. Chorda tympani.
12. After a cold a patient has a feeling of facial
numbness on the right. Examination has shown
disorders of pain and temperature sensitivity of
the right half of the face. Which nerve has been
injured?
A. Sublingual.
B. Facial.
C. Glossopharyngeal.
D. Vagus.
E. *Trigeminal.
13. A patient with epidemic encephalitis has uni- or
bilateral ptosis (blepharoptosis), divergent strabismus, accommodation disorder, mydriatic
pupils. The nuclei of what pair of cranial nerves
have been affected?
A. *III.
B. IV.
C. V.
D. VI.
E. VII.
14. As a result of a pathological process the function of the efferent part central link of the vegetative nervous system sympathetic department
was affected. Point out possible localization of
the process in the spinal cord.
A. *Lateral intermediate nucleus of lateral
horns.
B. Medial intermediate nucleus of lateral
horns.
C. Dorsal nucleus of posterior horns.
D. Proper nucleus of posterior horns.
E. Central nucleus of anterior horns.
15. After an oral cavity soft tissues injure a patient
lost gustation of the posterior third of the
tongue. What nerve was injured?
A. *Glossopharyngeal.
B. Facial.
C. Hypoglossal.
D. Lingual.
E. Chorda tympani.
16. A head trauma caused a hematoma in the zone
of the middle cranial fossa on the left which led
to a mydriatic pupil on the affected side. What
nerve was injured?
A. Trigeminal.
B. Abducent.
C. Ophthalmic.
D. Trochlear.
E. *Oculomotor.
17. During the initial examination a patient does
not have general sensitivity of the anterior 2/3
of the tongue. Gustation is preserved. What
nerve was injured?
A. *Lingual branch of trigeminal nerve up to
its conjugation with chorda tympani.
B. Sublingual nerve.
C. Lingual branch of trigeminal nerve after its
conjugation with chorda tympani.
D. Chorda tympani of facial nerve.
E. Glossopharyngeal nerve.
18. A patient has lacrimation and increased salivation. In combination with other symptoms this
state is considered to be an irritation of fibers of
a cranial nerve. Which nerve is this, and what
fibers are these?
A. *Parasympathetic fibres of facial nerve.
B. Parasympathetic fibres of oculomotor
nerve.
C. Somatic motor fibres of oculomotor nerve.
D. Parasympathetic fibres of vagus nerve.
E. Somatic motor fibres of facial nerve.
19. Examination of pupillary reflex has shown asthenocoria. Which nucleus function is damaged?
A. *Accessory nucleus of oculomotor nerve.
B. Nucleus of trochlear nerve.
C. Nucleus of abducent nerve.
D. Nucleus of superior tubercles of tectum of
mesencephalon.
E. Nucleus of oculomotor nerve.
UNIT 14. THE VESSELS OF HEAD AND NECK
Practice class 12. Written tests and examination of practice skills of cranial nerves. Examination of self-taught tasks. The arch of aorta. The common carotid and subclavian arteries.
The aim: to learn the characteristic of the arch of aorta; to learn the topography, branches and area of
blood supply of the subclavian and common carotid artery .
Professional orientation: the knowledge of this topic is necessary for doctors of all specialities; it represents special interest for therapists.
The plan of the practice class:
A. Checking of the home assignment: oral quiz or written test control – 30 minutes.
B. Summary lecture on the topic by teacher – 30 minutes.
a) The arch of aorta, its topography, peculiarities and branches.
b) The subclavian artery, its topography, peculiarities and branches.
c) The common carotid artery, its topography, peculiarities and branches.
C. Students’ self-taught time – 55 minutes
D. Home-task – 5 minutes
The Arch of the Aorta (Arcus Aortae; Transverse Aorta).—The arch of the aorta begins at the level of the upper border of the second sternocostal articulation of the right side, and runs at first upward, backward, and to the left in
front of the trachea; it is then directed backward on the left side of the trachea and finally passes downward on the left side
of the body of the fourth thoracic vertebra, at the lower border of which it becomes continuous with the descending aorta. It
thus forms two curvatures: one with its convexity upward, the other with its convexity forward and to the left. Its upper
border is usually about 2.5 cm. below the superior border to the manubrium sterni.
Relations.—The arch of the aorta is covered anteriorly by the pleurae and anterior margins of the lungs, and by the
remains of the thymus. As the vessel runs backward its left side is in contact with the left lung and pleura. Passing downward on the left side of this part of the arch are four nerves; in order from before backward these are, the left phrenic, the
lower of the superior cardiac branches of the left vagus, the superior cardiac branch of the left sympathetic, and the trunk of
the left vagus. As the last nerve crosses the arch it gives off its recurrent branch, which hooks around below the vessel and
then passes upward on its right side. The highest left intercostal vein runs obliquely upward and forward on the left side of
the arch, between the phrenic and vagus nerves. On the right are the deep part of the cardiac plexus, the left recurrent nerve,
the esophagus, and the thoracic duct; the trachea lies behind and to the right of the vessel. Above are the innominate, left
common carotid, and left subclavian arteries, which arise from the convexity of the arch and are crossed close to their origins by the left innominate vein. Below are the bifurcation of the pulmonary artery, the left bronchus, the ligamentum arteriosum, the superficial part of the cardiac plexus, and the left recurrent nerve. As already stated, the ligamentum arteriosum
connects the commencement of the left pulmonary artery to the aortic arch.
Between the origin of the left subclavian artery and the attachment of the ductus arteriosus the lumen of the fetal
aorta is considerably narrowed, forming what is termed the aortic isthmus, while immediately beyond the ductus arteriosus
the vessel presents a fusiform dilation which His has named the aortic spindle—the point of junction of the two parts being
marked in the concavity of the arch by an indentation or angle. These conditions persist, to some extent, in the adult, where
His found that the average diameter of the spindle exceeded that of the isthmus by 3 mm.
Distinct from this diffuse and moderate stenosis at the isthmus is the condition known as coarctation of the aorta, or
marked stenosis often amounting to complete obliteration of its lumen, seen in adults and occuring at or near, oftenest a
little below, the insertion of the ligamentum arteriosum into the aorta. According to Bonnet 96 this coarctation is never
found in the fetus or at birth, and is due to an abnormal extension of the peculiar tissue of the ductus into the aortic wall,
which gives rise to a simultaneous stenosis of both vessels as it contracts after birth—the ductus is usually obliterated in
these cases. An extensive collateral circulation is set up, by the costocervicals, internal mammaries, and the descending
branches of the transverse cervical above the stenosis, and below it by the first four aortic intercostals, the pericardiacophrenics, and the superior and inferior epigastrics.
Peculiarities.—The height to which the aorta rises in the thorax is usually about 2.5 cm. below the upper border of
the sternum; but it may ascend nearly to the top of the bone. Occasionally it is found 4 cm., more rarely from 5 to 8 cm.
below this point. Sometimes the aorta arches over the root of the right lung (right aortic arch) instead of over that of the
left, and passes down on the right side of the vertebral column, a condition which is found in birds. In such cases all the
thoracic and abdominal viscera are transposed. Less frequently the aorta, after arching over the root of the right lung, is
directed to its usual position on the left side of the vertebral column; this peculiarity is not accompanied by transposition of
the viscera. The aorta occasionally divides, as in some quadrupeds, into an ascending and a descending trunk, the former of
which is directed vertically upward, and subdivides into three branches, to supply the head and upper extremities. Sometimes the aorta subdivides near its origin into two branches, which soon reunite. In one of these cases the esophagus and
trachea were found to pass through the interval between the two branches; this is the normal condition of the vessel in the
reptilia.
Branches.—The branches given off from the arch of the aorta are three in number: the innominate, the left common carotid, and the left subclavian.
Peculiarities.—Position of the Branches.—The branches, instead of arising from the highest part of the arch, may
spring from the commencement of the arch or upper part of the ascending aorta; or the distance between them at their ori-
gins may be increased or diminished, the most frequent change in this respect being the approximation of the left carotid
toward the innominate artery.
The number of the primary branches may be reduced to one, or more commonly two; the left carotid arising from
the innominate artery; or (more rarely) the carotid and subclavian arteries of the left side arising from a left innominate artery. But the number may be increased to four, from the right carotid and subclavian arteries arising directly from the aorta,
the innominate being absent. In most of these latter cases the right subclavian has been found to arise from the left end of
the arch; in other cases it is the second or third branch given off, instead of the first. Another common form in which there
are four primary branches is that in which the left vertebral artery arises from the arch of the aorta between the left carotid
and subclavian arteries. Lastly, the number of trunks from the arch may be increased to five or six; in these instances, the
external and internal carotids arise separately from the arch, the common carotid being absent on one or both sides. In some
few cases six branches have been found, and this condition is associated with the origin of both vertebral arteries from the
arch.
Number Usual, Arrangement Different.—When the aorta arches over to the right side, the three branches have an
arrangement the reverse of what is usual; the innominate artery is a left, one, and the right carotid and subclavian arise separately. In other cases, where the aorta takes its usual course, the two carotids may be joined in a common trunk, and the
subclavians arise separately from the arch, the right subclavian generally arising from the left end of the arch.
In some instances other arteries spring from the arch of the aorta. Of these the most common are the bronchial, one
or both, and the thyreoidea ima; but the internal mammary and the inferior thyroid have been seen to arise from this vessel.
The Subclavian Artery (A. Subclavia).—On the right side the subclavian artery arises from the innominate artery behind the right sternoclavicular articulation; on the left side it springs from the arch of the aorta. The two vessels,
therefore, in the first part of their course, differ in length, direction, and relation with neighboring structures.
In order to facilitate the description, each subclavian artery is divided into three parts. The first portion extends from
the origin of the vessel to the medial border of the Scalenus anterior; the second lies behind this muscle; and the third extends from the lateral margin of the muscle to the outer border of the first rib, where it becomes the axillary artery. The first
portions of the two vessels require separate descriptions; the second and third parts of the two arteries are practically alike.
First Part of the Right Subclavian Artery.—The first part of the right subclavian artery arises from the innominate artery, behind the upper part of the right sternoclavicular articulation, and passes upward and lateralward to the medial
margin of the Scalenus anterior. It ascends a little above the clavicle, the extent to which it does so varying in different cases.
Relations.—It is covered, in front, by the integument, superficial fascia, Platysma, deep fascia, the clavicular origin
of the Sternocleidomastoideus, the Sternohyoideus, and Sternothyreoideus, and another layer of the deep fascia. It is
crossed by the internal jugular and vertebral veins, by the vagus nerve and the cardiac branches of the vagus and sympathetic, and by the subclavian loop of the sympathetic trunk which forms a ring around the vessel. The anterior jugular vein
is directed lateralward in front of the artery, but is separated from it by the Sternohyoideus and Sternothyreoideus. Below
and behind the artery is the pleura, which separates it from the apex of the lung; behind is the sympathetic trunk, the Longus collie and the first thoracic vertebra. The right recurrent nerve winds around the lower and back part of the vessel.
First Part of the Left Subclavian Artery.—The first part of the left subclavian artery arises from the arch of the
aorta, behind the left common carotid, and at the level of the fourth thoracic vertebra; it ascends in the superior mediastinal
cavity to the root of the neck and then arches lateralward to the medial border of the Scalenus anterior.
Relations.—It is in relation, in front, with the vagus, cardiac, and phrenic nerves, which lie parallel with it, the left
common carotid artery, left internal jugular and vertebral veins, and the commencement of the left innominate vein, and is
covered by the Sternothyreoideus, Sternohyoideus, and Sternocleidomastoideus; behind, it is in relation with the esophagus,
thoracic duct, left recurrent nerve, inferior cervical ganglion of the sympathetic trunk, and Longus colli; higher up, however, the esophagus and thoracic duct lie to its right side; the latter ultimately arching over the vessel to join the angle of union between the subclavian and internal jugular veins. Medial to it are the esophagus, trachea, thoracic duct, and left recurrent nerve; lateral to it, the left pleura and lung.
Second and Third Parts of the Subclavian Artery.—The second portion of the subclavian artery lies behind the
Scalenus anterior; it is very short, and forms the highest part of the arch described by the vessel.
Relations.—It is covered, in front, by the skin, superficial fascia, Platysma, deep cervical fascia, Sternocleidomastoideus, and Scalenus anterior. On the right side of the neck the phrenic nerve is separated from the second part of the artery by the Scalenus anterior, while on the left side it crosses the first part of the artery close to the medial edge of the muscle. Behind the vessel are the pleura and the Scalenus medius; above, the brachial plexus of nerves; below, the pleura. The
subclavian vein lies below and in front of the artery, separated from it by the Scalenus anterior.
The third portion of the subclavian artery runs downward and lateralward from the lateral margin of the Scalenus
anterior to the outer border of the first rib, where it becomes the axillary artery. This is the most superficial portion of the
vessel, and is contained in the subclavian triangle.
Relations.—It is covered, in front, by the skin, the superficial fascia, the Platysma, the supraclavicular nerves, and
the deep cervical fascia. The external jugular vein crosses its medial part and receives the transverse scapular, transverse
cervical, and anterior jugular veins, which frequently form a plexus in front of the artery. Behind the veins, the nerve to the
Subclavius descends in front of the artery. The terminal part of the artery lies behind the clavicle and the Subclavius and is
crossed by the transverse scapular vessels. The subclavian vein is in front of and at a slightly lower level than the artery.
Behind, it lies on the lowest trunk of the brachial plexus, which intervenes between it and the Scalenus medius. Above and
to its lateral side are the upper trunks of the brachial plexus and the Omohyoideus. Below, it rests on the upper surface of
the first rib.
Peculiarities.—The subclavian arteries vary in their origin, their course, and the height to which they rise in the
neck.
The origin of the right subclavian from the innominate takes place, in some cases, above the sternoclavicular articulation, and occasionally, but less frequently, below that joint. The artery may arise as a separate trunk from the arch of the
aorta, and in such cases it may be either the first, second, third, or even the last branch derived from that vessel; in the majority, however, it is the first or last, rarely the second or third. When it is the first branch, it occupies the ordinary position
of the innominate artery; when the second or third, it gains its usual position by passing behind the right carotid; and when
the last branch, it arises from the left extremity of the arch, and passes obliquely toward the right side, usually behind the
trachea, esophagus, and right carotid, sometimes between the esophagus and trachea, to the upper border of the first rib,
whence it follows its ordinary course. In very rare instances, this vessel arises from the thoracic aorta, as low down as the
fourth thoracic vertebra. Occasionally, it perforates the Scalenus anterior; more rarely it passes in front of that muscle.
Sometimes the subclavian vein passes with the artery behind the Scalenus anterior. The artery may ascend as high as 4 cm.
above the clavicle, or any intermediate point between this and the upper border of the bone, the right subclavian usually
ascending higher than the left.
The left subclavian is occasionally joined at its origin with the left carotid.
The left subclavian artery is more deeply placed than the right in the first part of its course, and, as a rule, does not
reach quite as high a level in the neck. The posterior border of the Sternocleidomastoideus corresponds pretty closely to the
lateral border of the Scalenus anterior, so that the third portion of the artery, the part most accessible for operation, lies immediately lateral to the posterior border of the Sternocleidomastoideus.
Collateral Circulation.—After ligature of the third part of the subclavian artery, the collateral circulation is established mainly by three sets of vessels, thus described in a dissection:
1. A posterior set, consisting of the transverse scapular and the descending ramus of the transverse cervical branches
of the subclavian, anastomosing with the subscapular from the axillary.
2. A medial set, produced by the connection of the internal mammary on the one hand, with the highest intercostal
and lateral thoracic arteries, and the branches from the subscapular on the other.
3. A middle or axillary set, consisting of a number of small vessels derived from branches of the subclavian, above,
and, passing through the axilla, terminating either in the main trunk, or some of the branches of the axillary below. This last
set presented most conspicuously the peculiar character of newly formed or, rather, dilated arteries, being excessively tortuous, and forming a complete plexus.
The chief agent in the restoration of the axillary artery below the tumor was the subscapular artery, which communicated most freely with the internal mammary, transverse scapular and descending ramus of the transverse cervical branches
of the subclavian, from all of which it received so great an influx of blood as to dilate it to three times its natural size.
When a ligature is applied to the first part of the subclavian artery, the collateral circulation is carried on by: (1) the
anastomosis between the superior and inferior thyroids; (2) the anastomosis of the two vertebrals; (3) the anastomosis of the
internal mammary with the inferior epigastric and the aortic intercostals; (4) the costocervical anastomosing with the aortic
intercostals; (5) the profunda cervicis anastomosing with the descending branch of the occipital; (6) the scapular branches
of the thyrocervical trunk anastomosing with the branches of the axillary, and (7) the thoracic branches of the axillary anastomosing with the aortic intercostals.
Branches.—The branches of the subclavian artery are: Vertebral, Internal mammary, Thyrocervical, Costocervical.
On the left side all four branches generally arise from the first portion of the vessel; but on the right side the
costocervical trunk usually springs from the second portion of the vessel. On both sides of the neck, the first three branches
arise close together at the medial border of the Scalenus anterior; in the majority of cases, a free interval of from 1.25 to 2.5
cm. exists between the commencement of the artery and the origin of the nearest branch.
1. The vertebral artery (a. vertebralis), is the first branch of the subclavian, and arises from the upper and back
part of the first portion of the vessel. It is surrounded by a plexus of nerve fibers derived from the inferior cervical ganglion
of the sympathetic trunk, and ascends through the foramina in the transverse processes of the upper six cervical vertebrae it
then winds behind the superior articular process of the atlas and, entering the skull through the foramen magnum, unites, at
the lower border of the pons, with the vessel of the opposite side to form the basilar artery.
Relations.—The vertebral artery may be divided into four parts: The first part runs upward and backward between
the Longus colli and the Scalenus anterior. In front of it are the internal jugular and vertebral veins, and it is crossed by the
inferior thyroid artery; the left vertebral is crossed by the thoracic duct also. Behind it are the transverse process of the seventh cervical vertebra, the sympathetic trunk and its inferior cervical ganglion. The second part runs upward through the
foramina in the transverse processes of the upper six cervical vertebrae, and is surrounded by branches from the inferior
cervical sympathetic ganglion and by a plexus of veins which unite to form the vertebral vein at the lower part of the neck.
It is situated in front of the trunks of the cervical nerves, and pursues an almost vertical course as far as the transverse process of the atlas, above which it runs upward and lateralward to the foramen in the transverse process of the atlas. The third
part issues from the latter foramen on the medial side of the Rectus capitis lateralis, and curves backward behind the superior articular process of the atlas, the anterior ramus of the first cervical nerve being on its medial side; it then lies in the
groove on the upper surface of the posterior arch of the atlas, and enters the vertebral canal by passing beneath the posterior
atlantoöccipital membrane. This part of the artery is covered by the Semispinalis capitis and is contained in the suboccipital triangle—a triangular space bounded by the Rectus capitis posterior major, the Obliquus superior, and the Obliquus
inferior. The first cervical or suboccipital nerve lies between the artery and the posterior arch of the atlas. The fourth part
pierces the dura mater and inclines medialward to the front of the medulla oblongata; it is placed between the hypoglossal
nerve and the anterior root of the first cervical nerve and beneath the first digitation of the ligamentum denticulatum. At the
lower border of the pons it unites with the vessel of the opposite side to form the basilar artery.
Branches.—The branches of the vertebral artery may be divided into two sets: those given off in the neck, and those
within the cranium.
Cervical Branches. Spinal. Meningeal. Muscular.
Cranial Branches. Posterior Spinal. Anterior Spinal. Posterior Inferior Cerebellar. Medullary.
Spinal Branches (rami spinales) enter the vertebral canal through the intervertebral foramina, and each divides into
two branches. Of these, one passes along the roots of the nerves to supply the medulla spinalis and its membranes, anastomosing with the other arteries of the medulla spinalis; the other divides into an ascending and a descending branch, which
unite with similar branches from the arteries above and below, so that two lateral anastomotic chains are formed on the
posterior surfaces of the bodies of the vertebrae, near the attachment of the pedicles. From these anastomotic chains
branches are supplied to the periosteum and the bodies of the vertebrae, and others form communications with similar
branches from the opposite side; from these communications small twigs arise which join similar branches above and below, to form a central anastomotic chain on the posterior surface of the bodies of the vertebrae.
Muscular Branches are given off to the deep muscles of the neck, where the vertebral artery curves around the articular process of the atlas. They anastomose with the occipital, and with the ascending and deep cervical arteries.
The Meningeal Branch (ramus meningeus; posterior meningeal branch) springs from the vertebral opposite the foramen magnum, ramifies between the bone and dura mater in the cerebellar fossa, and supplies the falx cerebelli. It is frequently represented by one or two small branches.
The Posterior Spinal Artery (a. spinalis posterior; dorsal spinal artery) arises from the vertebral, at the side of the
medulla oblongata; passing backward, it descends on this structure, lying in front of the posterior roots of the spinal nerves,
and is reinforced by a succession of small branches, which enter the vertebral canal through the intervertebral foramina; by
means of these it is continued to the lower part of the medulla spinalis, and to the cauda equina. Branches from the posterior spinal arteries form a free anastomosis around the posterior roots of the spinal nerves, and communicate, by means of
very tortuous transverse branches, with the vessels of the opposite side. Close to its origin each gives off an ascending
branch, which ends at the side of the fourth ventricle.
The Anterior Spinal Artery (a. spinalis anterior; ventral spinal artery) is a small branch, which arises near the
termination of the vertebral, and, descending in front of the medulla oblongata, unites with its fellow of the opposite side at
the level of the foramen magnum. One of these vessels is usually larger than the other, but occasionally they are about
equal in size. The single trunk, thus formed, descends on the front of the medulla spinalis, and is reinforced by a succession
of small branches which enter the vertebral canal through the intervertebral foramina; these branches are derived from the
vertebral and the ascending cervical of the inferior thyroid in the neck; from the intercostals in the thorax; and from the
lumbar, iliolumbar, and lateral sacral arteries in the abdomen and pelvis. They unite, by means of ascending and descending
branches, to form a single anterior median artery, which extend as far as the lower part of the medulla spinalis, and is continued as a slender twig on the filum terminale. This vessel is placed in the pia mater along the anterior median fissure; it
supplies that membrane, and the substance of the medulla spinalis, and sends off branches at its lower part to be distributed
to the cauda equina.
The Posterior Inferior Cerebellar Artery (a. cerebelli inferior posterior), the largest branch of the vertebral,
winds backward around the upper part of the medulla oblongata, passing between the origins of the vagus and accessory
nerves, over the inferior peduncle to the under surface of the cerebellum, where it divides into two branches. The medial
branch is continued backward to the notch between the two hemispheres of the cerebellum; while the lateral supplies the
under surface of the cerebellum, as far as its lateral border, where it anastomoses with the anterior inferior cerebellar and
the superior cerebellar branches of the basilar artery. Branches from this artery supply the choroid plexus of the fourth ventricle.
The Medullary Arteries (bulbar arteries) are several minute vessels which spring from the vertebral and its
branches and are distributed to the medulla oblongata.
The Basilar Artery (a. basilaris), so named from its position at the base of the skull, is a single trunk formed by the
junction of the two vertebral arteries: it extends from the lower to the upper border of the pons, lying in its median groove,
under cover of the arachnoid. It ends by dividing into the two posterior cerebral arteries.
Its branches, on either side, are the following: Pontine. Anterior Inferior Cerebellar. Internal Auditory. Superior
Cerebellar. Posterior Cerebral.
The pontine branches (rami ad pontem; transverse branches) are a number of small vessels which come off at right
angles from either side of the basilar artery and supply the pons and adjacent parts of the brain.
The internal auditory artery (a. auditiva interna; auditory artery), a long slender branch, arises from near the
middle of the artery; it accompanies the acoustic nerve through the internal acoustic meatus, and is distributed to the internal ear.
The anterior inferior cerebellar artery (a. cerebelli inferior anterior) passes backward to be distributed to the anterior part of the under surface of the cerebellum, anastomosing with the posterior inferior cerebellar branch of the vertebral.
The superior cerebellar artery (a. cerebelli superior) arises near the termination of the basilar. It passes lateralward, immediately below the oculomotor nerve, which separates it from the posterior cerebral artery, winds around the cerebral peduncle, close to the trochlear nerve, and, arriving at the upper surface of the cerebellum, divides into branches
which ramify in the pia mater and anastomose with those of the inferior cerebellar arteries. Several branches are given to
the pineal body, the anterior medullary velum, and the tela chorioidea of the third ventricle.
The posterior cerebral artery (a. cerebri posterior) is larger than the preceding, from which it is separated near its
origin by the oculomotor nerve. Passing lateralward, parallel to the superior cerebellar artery, and receiving the posterior
communicating from the internal carotid, it winds around the cerebral peduncle, and reaches the tentorial surface of the
occipital lobe of the cerebrum, where it breaks up into branches for the supply of the temporal and occipital lobes.
The branches of the posterior cerebral artery are divided into two sets, ganglionic and cortical:
Ganglionic - Posterior-medial.
Cortical - Anterior Temporal, Posterior Choroidal, Posterior Temporal, Postero-lateral, Calcarine, Parietoöccipital.
Ganglionic.—The postero-medial ganglionic branches are a group of small arteries which arise at the commencement of the posterior cerebral artery: these, with similar branches from the posterior communicating, pierce the posterior perforated substance, and supply the medial surfaces of the thalami and the walls of the third ventricle. The posterior
choroidal branches run forward beneath the splenium of the corpus callosum, and supply the tela chorioidea of the third
ventricle and the choroid plexus. The postero-lateral ganglionic branches are small arteries which arise from the posterior cerebral artery after it has turned around the cerebral peduncle; they supply a considerable portion of the thalamus.
Cortical.—The cortical branches are: the anterior temporal, distributed to the uncus and the anterior part of the fusiform gyrus; the posterior temporal, to the fusiform and the inferior temporal gyri; the calcarine, to the cuneus and gyrus
lingualis and the back part of the convex surface of the occipital lobe; and the parietoöccipital, to the cuneus and the
precuneus.
2. The thyrocervical trunk (truncus thyreocervicalis; thyroid axis) is a short thick trunk, which arises from the
front of the first portion of the subclavian artery, close to the medial border of the Scalenus anterior, and divides almost
immediately into three branches, the inferior thyroid, transverse scapular, and transverse cervical.
The Inferior Thyroid Artery (a. thyreoidea inferior) passes upward, in front of the vertebral artery and Longus
colli; then turns medialward behind the carotid sheath and its contents, and also behind the sympathetic trunk, the middle
cervical ganglion resting upon the vessel. Reaching the lower border of the thyroid gland it divides into two branches,
which supply the postero-inferior parts of the gland, and anastomose with the superior thyroid, and with the corresponding
artery of the opposite side. The recurrent nerve passes upward generally behind, but occasionally in front, of the artery.
The branches of the inferior thyroid are: Inferior Laryngeal, Esophageal, Tracheal, Ascending Cervical, Muscular.
The inferior laryngeal artery (a. laryngea inferior) ascends upon the trachea to the back part of the larynx under
cover of the Constrictor pharyngis inferior, in company with the recurrent nerve, and supplies the muscles and mucous
membrane of this part, anastomosing with the branch from the opposite side, and with the superior laryngeal branch of the
superior thyroid artery.
The tracheal branches (rami tracheales) are distributed upon the trachea, and anastomose below with the bronchial
arteries.
The esophageal branches (rami aesophagei) supply the esophagus, and anastomose with the esophageal branches
of the aorta.
The ascending cervical artery (a. cervicalis ascendens) is a small branch which arises from the inferior thyroid as
that vessel is passing behind the carotid sheath; it runs up on the anterior tubercles of the transverse processes of the cervical vertebrae in the interval between the Scalenus anterior and Longus capitis. To the muscles of the neck it gives twigs
which anastomose with branches of the vertebral, and it sends one or two spinal branches into the vertebral canal through
the intervertebral foramina to be distributed to the medulla spinalis and its membranes, and to the bodies of the vertebrae, in
the same manner as the spinal branches from the vertebral. It anastomoses with the ascending pharyngeal and occipital arteries.
The muscular branches supply the depressors of the hyoid bone, and the Longus colli, Scalenus anterior, and Constrictor pharyngis inferior.
The Transverse Scapular Artery (a. transversa scapulae suprascapular artery) passes at first downward and lateralward across the Scalenus anterior and phrenic nerve, being covered by the Sternocleidomastoideus; it then crosses the
subclavian artery and the brachial plexus, and runs behind and parallel with the clavicle and Subclavius, and beneath the
inferior belly of the Omohyoideus, to the superior border of the scapula; it passes over the superior transverse ligament of
the scapula which separates it from the suprascapular nerve, and enters the supraspinatous fossa. In this situation it lies
close to the bone, and ramifies between it and the Supraspinatus, to which it supplies branches. It then descends behind the
neck of the scapula, through the great scapular notch and under cover of the inferior transverse ligament, to reach the infraspinatous fossa, where it anastomoses with the scapular circumflex and the descending branch of the transverse cervical.
Besides distributing branches to the Sternocleidomastoideus, Subclavius, and neighboring muscles, it gives off a suprasternal branch, which crosses over the sternal end of the clavicle to the skin of the upper part of the chest; and an acromial
branch, which pierces the Trapezius and supplies the skin over the acromion, anastomosing with the thoracoacromial artery. As the artery passes over the superior transverse ligament of the scapula, it sends a branch into the subscapular fossa,
where it ramifies beneath the Subscapularis, and anastomoses with the subscapular artery and with the descending branch
of the transverse cervical. It also sends articular branches to the acromioclavicular and shoulder-joints, and a nutrient artery
to the clavicle.
The Transverse Cervical Artery (a. transversa colli; transversalis colli artery) lies at a higher level than the transverse scapular; it passes transversely above the inferior belly of the Omohyoideus to the anterior margin of the Trapezius,
beneath which it divides into an ascending and a descending branch. It crosses in front of the phrenic nerve and the Scaleni, and in front of or between the divisions of the brachial plexus, and is covered by the Platysma and Sternocleidomastoideus, and crossed by the Omohyoideus and Trapezius.
The ascending branch (ramus ascendens; superficial cervical artery) ascends beneath the anterior margin of the
Trapezius, distributing branches to it, and to the neighboring muscles and lymph glands in the neck, and anastomosing with
the superficial branch of the descending ramus of the occipital artery.
The descending branch (ramus descendens; posterior scapular artery) passes beneath the Levator scapulae to the
medial angle of the scapula, and then descends under the Rhomboidei along the vertebral border of that bone as far as the
inferior angle. It supplies the Rhomboidei, Latissimus dorsi and Trapezius, and anastomoses with the transverse scapular
and subscapular arteries, and with the posterior branches of some of the intercostal arteries.
Peculiarities.—The ascending branch of the transverse cervical frequently arises directly from the thyrocervical
trunk; and the descending branch from the third, more rarely from the second, part of the subclavian.
3. The internal mammary artery (a. mammaria interna) arises from the under surface of the first portion of the
subclavian, opposite the thyrocervical trunk. It descends behind the cartilages of the upper six ribs at a distance of about
1.25 cm. from the margin of the sternum, and at the level of the sixth intercostal space divides into the musculophrenic
and superior epigastric arteries.
Relations.—It is directed at first downward, forward, and medialward behind the sternal end of the clavicle, the
subclavian and internal jugular veins, and the first costal cartilage, and passes forward close to the lateral side of the innominate vein. As it enters the thorax the phrenic nerve crosses from its lateral to its medial side. Below the first costal cartilage
it descends almost vertically to its point of bifurcation. It is covered in front by the cartilages of the upper six ribs and the
intervening Intercostales interni and anterior intercostal membranes, and is crossed by the terminal portions of the upper six
intercostal nerves. It rests on the pleura, as far as the third costal cartilage; below this level, upon the Transversus thoracis.
It is accompanied by a pair of veins; these unite above to form a single vessel, which runs medial to the artery and ends in
the corresponding innominate vein.
Branches.—The branches of the internal mammary are: Pericardiacophrenic, Intercostal, Anterior Mediastinal, Perforating, Pericardial, Musculophrenic, Sternal, Superior Epigastric.
The Pericardiacophrenic Artery (a. pericardiacophrenica; a. comes nervi phrenici) is a long slender branch,
which accompanies the phrenic nerve, between the pleura and pericardium, to the diaphragm, to which it is distributed; it
anastomoses with the musculophrenic and inferior phrenic arteries.
The Anterior Mediastinal Arteries (aa. mediastinales anteriores; mediastinal arteries) are small vessels, distributed to the areolar tissue and lymph glands in the anterior mediastinal cavity, and to the remains of the thymus.
The Pericardial Branches supply the upper part of the anterior surface of the pericardium; the lower part receives
branches from the musculophrenic artery.
The Sternal Branches (rami sternales) are distributed to the Transversus thoracis, and to the posterior surface of the
sternum.
The anterior mediastinal, pericardial, and sternal branches, together with some twigs from the pericardiacophrenic,
anastomose with branches from the intercostal and bronchial arteries, and form a subpleural mediastinal plexus.
The Intercoastal Branches (rami intercostales; anterior intercostal arteries) supply the upper five or six intercostal
spaces. Two in number in each space, these small vessels pass lateralward, one lying near the lower margin of the rib
above, and the other near the upper margin of the rib below, and anastomose with the intercostal arteries from the aorta.
They are at first situated between the pleura and the Intercostales interni, and then between the Intercostales interni and
externi. They supply the Intercostales and, by branches which perforate the Intercostales externi, the Pectorales and the
mamma.
The Perforating Branches (rami perforantes) correspond to the five or six intercostal spaces. They pass forward
through the intercostal spaces, and, curving lateralward, supply the Pectoralis major and the integument. Those which correspond to the second, third, and fourth spaces give branches to the mamma, and during lactation are of large size.
The Musculophrenic Artery (a. musculophrenica) is directed obliquely downward and lateralward, behind the cartilages of the false ribs; it perforates the diaphragm at the eighth or ninth costal cartilage, and ends, considerably reduced in
size, opposite the last intercostal space. It gives off intercostal branches to the seventh, eighth, and ninth intercostal spaces;
these diminish in size as the spaces decrease in length, and are distributed in a manner precisely similar to the intercostals
from the internal mammary. The musculophrenic also gives branches to the lower part of the pericardium, and others which
run backward to the diaphragm, and downward to the abdominal muscles.
The Superior Epigastric Artery (a. epigastrica superior) continues in the original direction of the internal mammary; it descends through the interval between the costal and sternal attachments of the diaphragm, and enters the sheath of
the Rectus abdominis, at first lying behind the muscle, and then perforating and supplying it, and anastomosing with the
inferior epigastric artery from the external iliac. Branches perforate the anterior wall of the sheath of the Rectus, and supply
the muscles of the abdomen and the integument, and a small branch passes in front of the xiphoid process and anastomoses
with the artery of the opposite side. It also gives some twigs to the diaphragm, while from the artery of the right side small
branches extend into the falciform ligament of the liver and anastomose with the hepatic artery.
4. The costocervical trunk (truncus costocervicalis; superior intercostal artery) arises from the upper and back
part of the subclavian artery, behind the Scalenus anterior on the right side, and medial to that muscle on the left side. Passing backward, it gives off the profunda cervicalis, and, continuing as the highest intercostal artery, descends behind the
pleura in front of the necks of the first and second ribs, and anastomoses with the first aortic intercostal. As it crosses the
neck of the first rib it lies medial to the anterior division of the first thoracic nerve, and lateral to the first thoracic ganglion
of the sympathetic trunk.
In the first intercostal space, it gives off a branch which is distributed in a manner similar to the distribution of the
aortic intercostals. The branch for the second intercostal space usually joins with one from the highest aortic intercostal
artery. This branch is not constant, but is more commonly found on the right side; when absent, its place is supplied by an
intercostal branch from the aorta. Each intercostal gives off a posterior branch which goes to the posterior vertebral muscles, and sends a small spinal branch through the corresponding intervertebral foramen to the medulla spinalis and its
membranes.
The Profunda Cervicalis (a. cervicalis profunda; deep cervical branch) arises, in most cases, from the costocervical trunk, and is analogous to the posterior branch of an aortic intercostal artery: occasionally it is a separate branch from
the subclavian artery. Passing backward, above the eighth cervical nerve and between the transverse process of the seventh
cervical vertebra and the neck of the first rib, it runs up the back of the neck, between the Semispinales capitis and colli, as
high as the axis vertebra, supplying these and adjacent muscles, and anastomosing with the deep division of the descending
branch of the occipital, and with branches of the vertebral. It gives off a spinal twig which enters the canal through the intervertebral foramen between the seventh cervical and first thoracic vertebrae.
Note. The vertebral artery sometimes enters the foramen in the transverse process of the fifth vertebra, and has been
seen entering that of the seventh vertebra.
The Common Carotid Artery
The principal arteries of supply to the head and neck are the two common carotids; they ascend in the neck and
each divides into two branches, viz., (1) the external carotid, supplying the exterior of the head, the face, and the greater
part of the neck; (2) the internal carotid, supplying to a great extent the parts within the cranial and orbital cavities.
The Common Carotid Artery (A. Carotis Communis)—The common carotid arteries differ in length and in
their mode of origin. The right begins at the bifurcation of the innominate artery behind the sternoclavicular joint and is
confined to the neck. The left springs from the highest part of the arch of the aorta to the left of, and on a plane posterior to
the innominate artery, and therefore consists of a thoracic and a cervical portion.
The thoracic portion of the left common carotid artery ascends from the arch of the aorta through the superior
mediastinum to the level of the left sternoclavicular joint, where it is continuous with the cervical portion.
1. Relations.—In front, it is separated from the manubrium sterni by the Sternohyoideus and Sternothyreoideus,
the anterior portions of the left pleura and lung, the left innominate vein, and the remains of the thymus; behind, it lies on
the trachea, esophagus, left recurrent nerve, and thoracic duct. To its right side below is the innominate artery, and above,
the trachea, the inferior thyroid veins, and the remains of the thymus; to its left side are the left vagus and phrenic nerves,
left pleura, and lung. The left subclavian artery is posterior and slightly lateral to it.
The cervical portions of the common carotids resemble each other so closely that one description will apply to
both. Each vessel passes obliquely upward, from behind the sternoclavicular articulation, to the level of the upper border of
the thyroid cartilage, where it divides into the external and internal carotid arteries.
At the lower part of the neck the two common carotid arteries are separated from each other by a very narrow interval which contains the trachea; but at the upper part, the thyroid gland, the larynx and pharynx project forward between
the two vessels. The common carotid artery is contained in a sheath, which is derived from the deep cervical fascia and
encloses also the internal jugular vein and vagus nerve, the vein lying lateral to the artery, and the nerve between the artery
and vein, on a plane posterior to both. On opening the sheath, each of these three structures is seen to have a separate fibrous investment.
Relations.—At the lower part of the neck the common carotid artery is very deeply seated, being covered by the
integument, superficial fascia, Platysma, and deep cervical fascia, the Sternocleidomastoideus, Sternohyoideus, Sternothyreoideus, and Omohyoideus; in the upper part of its course it is more superficial, being covered merely by the integument,
the superficial fascia, Platysma, deep cervical fascia, and medial margin of the Sternocleidomastoideus. When the latter
muscle is drawn backward, the artery is seen to be contained in a triangular space, the carotid triangle, bounded behind by
the Sternocleidomastoideus, above by the Stylohyoideus and posterior belly of the Digastricus, and below by the superior
belly of the Omohyoideus. This part of the artery is crossed obliquely, from its medial to its lateral side, by the sternocleidomastoid branch of the superior thyroid artery; it is also crossed by the superior and middle thyroid veins which end
in the internal jugular; descending in front of its sheath is the descending branch of the hypoglossal nerve, this filament
being joined by one or two branches from the cervical nerves, which cross the vessel obliquely. Sometimes the descending
branch of the hypoglossal nerve is contained within the sheath. The superior thyroid vein crosses the artery near its termination, and the middle thyroid vein a little below the level of the cricoid cartilage; the anterior jugular vein crosses the artery
just above the clavicle, but is separated from it by the Sternohyoideus and Sternothyreoideus. Behind, the artery is separated from the transverse processes of the cervical vertebrae by the Longus colli and Longus capitis, the sympathetic trunk
being interposed between it and the muscles. The inferior thyroid artery crosses behind the lower part of the vessel. Medially, it is in relation with the esophagus, trachea, and thyroid gland (which overlaps it), the inferior thyroid artery and recurrent nerve being interposed; higher up, with the larynx and pharynx. Lateral to the artery are the internal jugular vein and
vagus nerve.
At the lower part of the neck, the right recurrent nerve crosses obliquely behind the artery; the right internal jugular vein diverges from the artery, but the left approaches and often overlaps the lower part of the artery.
Behind the angle of bifurcation of the common carotid artery is a reddish-brown oval body, known as the glomus
caroticum (carotid body). It is similar in structure to the glomus coccygeum (coccygeal body) which is situated on the
middle sacral artery.
Peculiarities as to Origin.—The right common carotid may arise above the level of the upper border of the sternoclavicular articulation; this variation occurs in about 12 per cent. of cases. In other cases the artery may arise as a separate branch from the arch of the aorta, or in conjunction with the left carotid. The left common carotid varies in its origin
more than the right. In the majority of abnormal cases it arises with the innominate artery; if that artery is absent, the two
carotids arise usually by a single trunk. It is rarely joined with the left subclavian, except in cases of transposition of the
aortic arch.
Peculiarities as to Point of Division.—In the majority of abnormal cases this occurs higher than usual, the artery
dividing opposite or even above the hyoid bone; more rarely, it occurs below, opposite the middle of the larynx, or the lower border of the cricoid cartilage; one case is related by Morgagni, where the artery was only 4 cm. in length and divided at
the root of the neck. Very rarely, the common carotid ascends in the neck without any subdivision, either the external or the
internal carotid being wanting; and in a few cases the common carotid has been found to be absent, the external and internal
carotids arising directly from the arch of the aorta. This peculiarity existed on both sides in some instances, on one side in
others.
Occasional Branches.—The common carotid usually gives off no branch previous to its bifurcation, but it occasionally gives origin to the superior thyroid or its laryngeal branch, the ascending pharyngeal, the inferior thyroid, or, more
rarely, the vertebral artery.
Collateral Circulation.—After ligature of the common carotid, the collateral circulation can be perfectly established, by the free communication which exists between the carotid arteries of opposite sides, both without and within the
cranium, and by enlargement of the branches of the subclavian artery on the side corresponding to that on which the vessel
has been tied. The chief communications outside the skull take place between the superior and inferior thyroid arteries, and
the profunda cervicis and ramus descendens of the occipital; the vertebral takes the place of the internal carotid within the
cranium.
Practice skills
Students are supposed to identify the following structures on the samples:
Aorta
Subclavian artery (right, left)
- aortic bulb
- vertebral artery
- ascending aorta
- basilar artery
- arch of aorta
- posterior cerebral artery
- branches of aortic arch
- internal thoracic artery
- descending aorta
- thyrocervical trunk
- thoracic aorta
- inferior thyroid artery
Brachiocephalic trunk
- costocervical trunk
- right common carotid artery
- transverse cervical artery
- right subclavian artery
- cerebral arterial circle
Common carotid artery (right, left)
Practice class 13. The internal carotid arteries: relations, anastomoses, branches. The supplement of the brain and meninges.
The aim: to learn the characteristic of the internal carotid artery, to learn its topography, branches and area of blood supply.
Professional orientation: the knowledge of this topic is necessary for doctors of all specialities; it represents special interest for therapists.
The plan of the practice class:
A. Checking of the home assignment: oral quiz or written test control – 30 minutes.
B. Summary lecture on the topic by teacher – 30 minutes.
a) The course and relations of the internal carotid artery.
b) The branches of the internal carotid artery.
c) Blood supply of the brain and meninges.
C. Students’ self-taught time – 55 minutes
D. Home-task – 5 minutes
The Internal Carotid Artery (A. Carotis Interna)
The internal carotid artery supplies the anterior part of the brain, the eye and its appendages, and sends branches to
the forehead and nose. Its size, in the adult, is equal to that of the external carotid, though, in the child, it is larger than that
vessel. It is remarkable for the number of curvatures that it presents in different parts of its course. It occasionally has one
or two flexures near the base of the skull, while in its passage through the carotid canal and along the side of the body of
the sphenoid bone it describes a double curvature and resembles the italic letter S.
Course and Relations.—In considering the course and relations of this vessel it may be divided into four portions:
cervical, petrous, cavernous, and cerebral.
Cervical Portion.—This portion of the internal carotid begins at the bifurcation of the common carotid, opposite the
upper border of the thyroid cartilage, and runs perpendicularly upward, in front of the transverse processes of the upper
three cervical vertebrae, to the carotid canal in the petrous portion of the temporal bone. It is comparatively superficial at its
commencement, where it is contained in the carotid triangle, and lies behind and lateral to the external carotid, overlapped
by the Sternocleidomastoideus, and covered by the deep fascia, Platysma, and integument: it then passes beneath the parotid gland, being crossed by the hypoglossal nerve, the Digastricus and Stylohyoideus, and the occipital and posterior auricular arteries. Higher up, it is separated from the external carotid by the Styloglossus and Stylopharyngeus, the tip of the styloid process and the stylohyoid ligament, the glossopharyngeal nerve and the pharyngeal branch of the vagus. It is in relation, behind, with the Longus capitis, the superior cervical ganglion of the sympathetic trunk, and the superior laryngeal
nerve; laterally, with the internal jugular vein and vagus nerve, the nerve lying on a plane posterior to the artery; medially,
with the pharynx, superior laryngeal nerve, and ascending pharyngeal artery. At the base of the skull the glossopharyngeal,
vagus, accessory, and hypoglossal nerves lie between the artery and the internal jugular vein.
Petrous Portion.—When the internal carotid artery enters the canal in the petrous portion of the temporal bone, it
first ascends a short distance, then curves forward and medialward, and again ascends as it leaves the canal to enter the cavity of the skull between the lingula and petrosal process of the sphenoid. The artery lies at first in front of the cochlea and
tympanic cavity; from the latter cavity it is separated by a thin, bony lamella, which is cribriform in the young subject, and
often partly absorbed in old age. Farther forward it is separated from the semilunar ganglion by a thin plate of bone, which
forms the floor of the fossa for the ganglion and the roof of the horizontal portion of the canal. Frequently this bony plate is
more or less deficient, and then the ganglion is separated from the artery by fibrous membrane. The artery is separated from
the bony wall of the carotid canal by a prolongation of dura mater, and is surrounded by a number of small veins and by
filaments of the carotid plexus, derived from the ascending branch of the superior cervical ganglion of the sympathetic
trunk.
Cavernous Portion.—In this part of its course, the artery is situated between the layers of the dura mater forming
the cavernous sinus, but covered by the lining membrane of the sinus. It at first ascends toward the posterior clinoid process, then passes forward by the side of the body of the sphenoid bone, and again curves upward on the medial side of the
anterior clinoid process, and perforates the dura mater forming the roof of the sinus. This portion of the artery is surrounded
by filaments of the sympathetic nerve, and on its lateral side is the abducent nerve.
Cerebral Portion.—Having perforated the dura mater on the medial side of the anterior clinoid process, the internal
carotid passes between the optic and oculomotor nerves to the anterior perforated substance at the medial extremity of the
lateral cerebral fissure, where it gives off its terminal or cerebral branches.
Peculiarities.—The length of the internal carotid varies according to the length of the neck, and also according to
the point of bifurcation of the common carotid. It arises sometimes from the arch of the aorta; in such rare instances, this
vessel has been found to be placed nearer the middle line of the neck than the external carotid, as far upward as the larynx,
when the latter vessel crossed the internal carotid. The course of the artery, instead of being straight, may be very tortuous.
A few instances are recorded in which this vessel was altogether absent; in one of these the common carotid passed up the
neck, and gave off the usual branches of the external carotid; the cranial portion of the internal carotid was replaced by two
branches of the internal maxillary, which entered the skull through the foramen rotundum and foramen ovale, and joined to
form a single vessel.
Branches.—The cervical portion of the internal carotid gives off no branches. Those from the other portions are:
From the Petrous Portion – Caroticotympanic, Artery of the Pterygoid Canal.
From the Cavernous Portion – Cavernous, Hypophyseal, Semilunar, Anterior Meningeal, Ophthalmic.
From the Cerebral Portion - Anterior Cerebral, Middle Cerebral, Posterior Communicating, Choroidal.
1. The caroticotympanic branch (ramus caroticotympanicus; tympanic branch) is small; it enters the tympanic
cavity through a minute foramen in the carotid canal, and anastomoses with the anterior tympanic branch of the internal
maxillary, and with the stylomastoid artery.
2. The artery of the pterygoid canal (a. canilis pterygoidei [Vidii]; Vidian artery) is a small, inconstant branch
which passes into the pterygoid canal and anastomoses with a branch of the internal maxillary artery.
3. The cavernous branches are numerous small vessels which supply the hypophysis, the semilunar ganglion, and
the walls of the cavernous and inferior petrosal sinuses. Some of them anastomose with branches of the middle meningeal.
4. The hypophyseal branches are one or two minute vessels supplying the hypophysis.
5. The semilunar branches are small vessels to the semilunar ganglion.
6. The anterior meningeal branch (a. meningea anterior) is a small branch which passes over the small wing of the
sphenoid to supply the dura mater of the anterior cranial fossa; it anastomoses with the meningeal branch from the posterior
ethmoidal artery.
7. The ophthalmic artery (a. ophthalmica) (Fig. 514) arises from the internal carotid, just as that vessel is emerging
from the cavernous sinus, on the medial side of the anterior clinoid process, and enters the orbital cavity through the optic
foramen, below and lateral to the optic nerve. It then passes over the nerve to reach the medial wall of the orbit, and thence
horizontally forward, beneath the lower border of the Obliquus superior, and divides it into two terminal branches, the
frontal and dorsal nasal. As the artery crosses the optic nerve it is accompanied by the nasociliary nerve, and is separated
from the frontal nerve by the Rectus superior and Levator palpebrae superioris.
Branches.—The branches of the ophthalmic artery may be divided into an orbital group, distributed to the orbit
and surrounding parts; and an ocular group, to the muscles and bulb of the eye.
Orbital Group - Lacrimal. Supraorbital. Posterior Ethmoidal. Anterior Ethmoidal. Medial Palpebral. Frontal. Dorsal
Nasal.
Ocular Group - Central Artery of the Retina. Short Posterior Ciliary. Long Posterior Ciliary. Anterior Ciliary. Muscular.
The Lacrimal Artery (a. lacrimalis) arises close to the optic foramen, and is one of the largest branches derived
from the ophthalmic: not infrequently it is given off before the artery enters the orbit. It accompanies the lacrimal nerve
along the upper border of the Rectus lateralis, and supplies the lacrimal gland. Its terminal branches, escaping from the
gland, are distributed to the eyelids and conjunctiva: of those supplying the eyelids, two are of considerable size and are
named the lateral palpebral arteries; they run medialward in the upper and lower lids respectively and anastomose with
the medial palpebral arteries, forming an arterial circle in this situation. The lacrimal artery give off one or two zygomatic
branches, one of which passes through the zygomatico-temporal foramen, to reach the temporal fossa, and anastomoses
with the deep temporal arteries; another appears on the cheek through the zygomatico-facial foramen, and anastomoses
with the transverse facial. A recurrent branch passes backward through the lateral part of the superior orbital fissure to the
dura mater, and anastomoses with a branch of the middle meningeal artery. The lacrimal artery is sometimes derived from
one of the anterior branches of the middle meningeal artery.
The Supraorbital Artery (a. supraorbitalis) springs from the ophthalmic as that vessel is crossing over the optic
nerve. It passes upward on the medial borders of the Rectus superior and Levator palpebrae, and meeting the supraorbital
nerve accompanies it between the periosteum and Levator palpebrae to the supraorbital foramen; passing through this it
divides into a superficial and a deep branch, which supply the integument, the muscles, and the pericranium of the forehead, anastomosing with the frontal, the frontal branch of the superficial temporal, and the artery of the opposite side. This
artery in the orbit supplies the Rectus superior and the Levator palpebrae, and sends a branch across the pulley of the
Obliquus superior, to supply the parts at the medial palpebral commissure. At the supraorbital foramen it frequently transmits a branch to the diploë.
The Ethmoidal Arteries are two in number: posterior and anterior. The posterior ethmoidal artery, the smaller,
passes through the posterior ethmoidal canal, supplies the posterior ethmoidal cells, and, entering the cranium, gives off a
meningeal branch to the dura mater, and nasal branches which descend into the nasal cavity through apertures in the cribriform plate, anastomosing with branches of the sphenopalatine. The anterior ethmoidal artery accompanies the nasociliary
nerve through the anterior ethmoidal canal, supplies the anterior and middle ethmoidal cells and frontal sinus, and, entering
the cranium, gives off a meningeal branch to the dura mater, and nasal branches; these latter descend into the nasal cavity
through the slit by the side of the crista galli, and, running along the groove on the inner surface of the nasal bone, supply
branches to the lateral wall and septum of the nose, and a terminal branch which appears on the dorsum of the nose between the nasal bone and the lateral cartilage.
The Medial Palpebral Arteries (aa. palpebrales mediales; internal palpebral arteries), two in number, superior
and inferior, arise from the ophthalmic, opposite the pulley of the Obliquus superior; they leave the orbit to encircle the
eyelids near their free margins, forming a superior and an inferior arch, which lie between the Orbicularis oculi and the
tarsi. The superior palpebral anastomoses, at the lateral angle of the orbit, with the zygomaticoörbital branch of the temporal artery and with the upper of the two lateral palpebral branches from the lacrimal artery; the inferior palpebral anastomoses, at the lateral angle of the orbit, with the lower of the two lateral palpebral branches from the lacrimal and with the
transverse facial artery, and, at the medial part of the lid, with a branch from the angular artery. From this last anastomoses
a branch passes to the nasolacrimal duct, ramifying in its mucous membrane, as far as the inferior meatus of the nasal cavity.
The Frontal Artery (a. frontalis), one of the terminal branches of the ophthalmic, leaves the orbit at its medial angle
with the supratrochlear nerve, and, ascending on the forehead, supplies the integument, muscles, and pericranium, anastomosing with the supraorbital artery, and with the artery of the opposite side.
The Dorsal Nasal Artery (a. dorsalis nasi; nasal artery), the other terminal branch of the ophthalmic, emerges from
the orbit above the medial palpebral ligament, and, after giving a twig to the upper part of the lacrimal sac, divides into two
branches, one of which crosses the root of the nose, and anastomoses with the angular artery, the other runs along the dorsum of the nose, supplies its outer surface; and anastomoses with the artery of the opposite side, and with the lateral nasal
branch of the external maxillary.
The Central Artery of the Retina (a. centralis retinœ) is the first and one of the smallest branches of the ophthalmic artery. It runs for a short distance within the dural sheath of the optic nerve, but about 1.25 cm. behind the eyeball it
pierces the nerve obliquely, and runs forward in the center of its substance to the retina. Its mode of distribution will be
described with the anatomy of the eye.
The Ciliary Arteries (aa. ciliares) are divisible into three groups, the long and short, posterior, and the anterior. The
short posterior ciliary arteries from six to twelve in number, arise from the ophthalmic, or its branches; they pass forward
around the optic nerve to the posterior part of the eyeball, pierce the sclera around the entrance of the nerve, and supply the
choroid and ciliary processes. The long posterior ciliary arteries, two in number, pierce the posterior part of the sclera at
some little distance from the optic nerve, and run forward, along either side of the eyeball, between the sclera and choroid,
to the ciliary muscle, where they divide into two branches; these form an arterial circle, the circulus arteriosus major,
around the circumference of the iris, from which numerous converging branches run, in the substance of the iris, to its pupillary margin, where they form a second arterial circle, the circulus arteriosus minor. The anterior ciliary arteries are
derived from the muscular branches; they run to the front of the eyeball in company with the tendons of the Recti, form a
vascular zone beneath the conjunctiva, and then pierce the sclera a short distance from the cornea and end in the circulus
arteriosus major.
The Muscular Branches, (rami musculares), two in number, superior and inferior, frequently spring from a common trunk. The superior, often wanting, supplies the Levator palpebrae superioris, Rectus superior, and Obliquus superior.
The inferior, more constantly present, passes forward between the optic nerve and Rectus inferior, and is distributed to the
Recti lateralis, medialis, and inferior, and the Obliquus inferior. This vessel gives off most of the anterior ciliary arteries.
Additional muscular branches are given off from the lacrimal and supraorbital arteries, or from the trunk of the ophthalmic.
8. The anterior cerebral artery (a. cerebri anterior) arises from the internal carotid, at the medial extremity of the
lateral cerebral fissure. It passes forward and medialward across the anterior perforated substance, above the optic nerve, to
the commencement of the longitudinal fissure. Here it comes into close relationship with the opposite artery, to which it is
connected by a short trunk, the anterior communicating artery. From this point the two vessels run side by side in the
longitudinal fissure, curve around the genu of the corpus callosum, and turning backward continue along the upper surface
of the corpus callosum to its posterior part, where they end by anastomosing with the posterior cerebral arteries.
Branches.—In its course the anterior cerebral artery gives off the following branches: Antero-medial Ganglionic,
Anterior, Posterior, Inferior, Middle.
The Antero-medial Ganglionic Branches are a group of small arteries which arise at the commencement of the anterior cerebral artery; they pierce the anterior perforated substance and lamina terminalis, and supply the rostrum of the
corpus callosum, the septum pellucidum, and the head of the caudate nucleus. The inferior branches, two or three in number, are distributed to the orbital surface of the frontal lobe, where they supply the olfactory lobe, gyrus rectus, and internal
orbital gyrus. The anterior branches supply a part of the superior frontal gyrus, and send twigs over the edge of the hemisphere to the superior and middle frontal gyri and upper part of the anterior central gyrus. The middle branches supply the
corpus callosum, the cingulate gyrus, the medial surface of the superior frontal gyrus, and the upper part of the anterior
central gyrus. The posterior branches supply the precuneus and adjacent lateral surface of the hemisphere.
The Anterior Communicating Artery (a. communicans anterior) connects the two anterior cerebral arteries across
the commencement of the longitudinal fissure. Sometimes this vessel is wanting, the two arteries joining together to form a
single trunk, which afterward divides; or it may be wholly, or partially, divided into two. Its length averages about 4 mm.,
but varies greatly. It gives off some of the antero-medial ganglionic vessels, but these are principally derived from the anterior cerebral.
9. The middle cerebral artery (a. cerebri media), the largest branch of the internal carotid, runs at first lateralward
in the lateral cerebral or Sylvian fissure and then backward and upward on the surface of the insula, where it divides into a
number of branches which are distributed to the lateral surface of the cerebral hemisphere
Branches.—The branches of this vessel are the: Antero-lateral Ganglionic, Inferior Lateral Frontal, Ascending Parietal, Parietotemporal, Ascending Frontal, Temporal.
The Antero-lateral Ganglionic Branches, a group of small arteries which arise at the commencement of the middle
cerebral artery, are arranged in two sets: one, the internal striate, passes upward through the inner segments of the lentiform nucleus, and supplies it, the caudate nucleus, and the internal capsule; the other, the external striate, ascends through
the outer segment of the lentiform nucleus, and supplies the caudate nucleus and the thalamus. One artery of this group is
of larger size than the rest, and is of special importance, as being the artery in the brain most frequently ruptured; it has
been termed by Charcot the artery of cerebral hemorrhage. It ascends between the lentiform nucleus and the external
capsule, and ends in the caudate nucleus. The inferior lateral frontal supplies the inferior frontal gyrus (Broca’s convolution) and the lateral part of the orbital surface of the frontal lobe. The ascending frontal supplies the anterior central gyrus.
The ascending parietal is distributed to the posterior central gyrus and the lower part of the superior parietal lobule. The
parietotemporal supplies the supramarginal and angular gyri, and the posterior parts of the superior and middle temporal
gyri. The temporal branches, two or three in number, are distributed to the lateral surface of the temporal lobe.
10. The posterior communicating artery (a. communicans posterior) runs backward from the internal carotid, and
anastomoses with the posterior cerebral, a branch of the basilar. It varies in size, being sometimes small, and occasionally
so large that the posterior cerebral may be considered as arising from the internal carotid rather than from the basilar. It is
frequently larger on one side than on the other. From its posterior half are given off a number of small branches, the postero-medial ganglionic branches, which, with similar vessels from the posterior cerebral, pierce the posterior perforated
substance and supply the medial surface of the thalami and the walls of the third ventricle.
11. The anterior choroidal (a. chorioidea; choroid artery) is a small but constant branch, which arises from the internal carotid, near the posterior communicating artery. Passing backward and lateralward between the temporal lobe and
the cerebral peduncle, it enters the inferior horn of the lateral ventricle through the choroidal fissure and ends in the choroid
plexus. It is distributed to the hippocampus, fimbria, tela chorioidea of the third ventricle, and choroid plexus.
Practice skills
Students are supposed to identify the following structures on the samples:
Internal carotid artery
- cerebral part
- cervical part
- ophthalmic artery
- petrous part
- anterior cerebral artery
- cavernous part
- posterior communicating artery
Practice class 14. The innervation and blood supplement of the orbital organs.
The aim: to learn the nerve and blood supply of the orbit and orbital organs.
Professional orientation: the knowledge of this topic is necessary for doctors of all specialities; it represents special interest for therapists, ophthalmologists and others.
The plan of the practice class:
A. Checking of the home assignment: oral quiz or written test control – 30 minutes.
B. Summary lecture on the topic by teacher – 30 minutes.
a) Nerve and blood supply of the walls of orbit.
b) Nerve and blood supply of the eyeball.
c) Nerves and vessels of the retina.
d) Nerve and blood supply of the eyelids.
e) Nerve and blood supply of the muscles of the eye.
f) Nerve and blood supply of the lacrimal gland.
C. Students’ self-taught time – 55 minutes
D. Home-task – 5 minutes
For more information see practice classes 8 (Review of cranial nerves. I, II, ІІІ, ІV, VI, ХІ, ХІІ pairs of
cranial nerves), 9 (V pair of cranial nerves: the trigeminal nerve), 13 (The internal carotid artery) and self-taught
classes 9 (Parasympathetic supplement of the head and neck), 10 (Sympathetic supplement of the head and
neck).
Practice class 15. The external carotid arteries: relations, anastomoses, branches, supplement. The innervation and blood supplement of the nasal cavity.
The aim: to learn the topography, branches and areas of blood supply of the external carotid artery; to
learn nerve and blood supply of the nasal cavity.
Professional orientation: the knowledge of this topic is necessary for doctors of all specialities; it represents special interest for therapists.
The plan of the practice class:
A. Checking of the home assignment: oral quiz or written test control – 30 minutes.
B. Summary lecture on the topic by teacher – 30 minutes.
a) The external carotid artery, its topography, branches and area of blood supply.
b) The anastomoses in the external carotid artery system.
c) The anastomoses between the systems of external carotid and subclavian arteries.
d) The anastomoses between the systems of external and internal carotid arteries.
e) Nerve and blood supply of the nasal cavity.
C. Students’ self-taught time – 55 minutes
D. Home-task – 5 minutes
The External Carotid Artery (A. Carotis Externa)
The external carotid artery begins opposite the upper border of the thyroid cartilage, and, taking a slightly curved
course, passes upward and forward, and then inclines backward to the space behind the neck of the mandible, where it divides into the superficial temporal and internal maxillary arteries. It rapidly diminishes in size in its course up the neck,
owing to the number and large size of the branches given off from it. In the child, it is somewhat smaller than the internal
carotid; but in the adult, the two vessels are of nearly equal size. At its origin, this artery is more superficial, and placed
nearer the middle line than the internal carotid, and is contained within the carotid triangle.
Relations.—The external carotid artery is covered by the skin, superficial fascia, Platysma, deep fascia, and anterior
margin of the Sternocleidomastoideus; it is crossed by the hypoglossal nerve, by the lingual, ranine, common facial, and
superior thyroid veins; and by the Digastricus and Stylohyoideus; higher up it passes deeply into the substance of the parotid gland, where it lies deep to the facial nerve and the junction of the temporal and internal maxillary veins. Medial to it are
the hyoid bone, the wall of the pharynx, the superior laryngeal nerve, and a portion of the parotid gland. Lateral to it, in the
lower part of its course, is the internal carotid artery. Posterior to it, near its origin, is the superior laryngeal nerve; and
higher up, it is separated from the internal carotid by the Styloglossus and Stylopharyngeus, the glossopharyngeal nerve,
the pharyngeal branch of the vagus, and part of the parotid gland.
Branches.—The branches of the external carotid artery may be divided into four sets.
Anterior - Superior Thyroid, Lingual, External Maxillary.
Posterior – Occipital, Posterior Auricular.
Ascending – Ascending Pharyngeal.
Terminal – Superficial Temporal, Internal Maxillary.
1. The superior thyroid artery (a. thyreoidea superior) arises from the external carotid artery just below the level
of the greater cornu of the hyoid bone and ends in the thyroid gland.
Relations.—From its origin under the anterior border of the Sternocleidomastoideus it runs upward and forward for
a short distance in the carotid triangle, where it is covered by the skin, Platysma, and fascia; it then arches downward beneath the Omohyoideus, Sternohyoideus, and Sternothyreoideus. To its medial side are the Constrictor pharyngis inferior
and the external branch of the superior laryngeal nerve.
Branches.—It distributes twigs to the adjacent muscles, and numerous branches to the thyroid gland, anastomosing
with its fellow of the opposite side, and with the inferior thyroid arteries. The branches to the gland are generally two in
number; one, the larger, supplies principally the anterior surface; on the isthmus of the gland it anastomoses with the corresponding artery of the opposite side: a second branch descends on the posterior surface of the gland and anastomoses with
the inferior thyroid artery.
Besides the arteries distributed to the muscles and to the thyroid gland, the branches of the superior thyroid are: Hyoid. Superior Laryngeal. Sternocleidomastoid. Cricothyroid.
The Hyoid Branch (ramus hyoideus; infrahyoid branch) is small and runs along the lower border of the hyoid bone
beneath the Thyreohyoideus and anastomoses with the vessel of the opposite side.
The Sternocleidomastoid Branch (ramus sternocleidomastoideus; sternomastoid branch) runs downward and lateralward across the sheath of the common carotid artery, and supplies the Sternocleidomastoideus and neighboring muscles
and integument; it frequently arises as a separate branch from the external carotid.
The Superior Laryngeal Artery (a. laryngea superior), larger than either of the preceding, accompanies the internal laryngeal branch of the superior laryngeal nerve, beneath the Thyreohyoideus; it pierces the hyothyroid membrane, and
supplies the muscles, mucous membrane, and glands of the larynx, anastomosing with the branch from the opposite side.
The Cricothyroid Branch (ramus cricothyreoideus) is small and runs transversely across the cricothyroid membrane, communicating with the artery of the opposite side.
2. The lingual artery (a. lingualis) arises from the external carotid between the superior thyroid and external maxillary; it first runs obliquely upward and medialward to the greater cornu of the hyoid bone; it then curves downward and
forward, forming a loop which is crossed by the hypoglossal nerve, and passing beneath the Digastricus and Stylohyoideus
it runs horizontally forward, beneath the Hyoglossus, and finally, ascending almost perpendicularly to the tongue, turns
forward on its lower surface as far as the tip, under the name of the profunda linguae.
Relations.—Its first, or oblique, portion is superficial, and is contained within the carotid triangle; it rests upon the
Constrictor pharyngis medius, and is covered by the Platysma and the fascia of the neck. Its second, or curved, portion also
lies upon the Constrictor pharyngis medius, being covered at first by the tendon of the Digastricus and by the Stylohyoideus, and afterward by the Hyoglossus. Its third, or horizontal, portion lies between the Hyoglossus and Genioglossus. The
fourth, or terminal part, under the name of the profunda linguae (ranine artery) runs along the under surface of the tongue
to its tip; here it is superficial, being covered only by the mucous membrane; above it is the Longitudinalis inferior, and on
the medial side the Genioglossus. The hypoglossal nerve crosses the first part of the lingual artery, but is separated from the
second part by the Hyoglossus.
Branches.—The branches of the lingual artery are: Hyoid. Sublingual. Dorsales linguae. Profunda linguae.
The Hyoid Branch (ramus hyoideus; suprahyoid branch) runs along the upper border of the hyoid bone, supplying
the muscles attached to it and anastomosing with its fellow of the opposite side.
The Arteriae Dorsales Linguae (rami dorsales linguae) consist usually of two or three small branches which arise
beneath the Hyoglossus; they ascend to the back part of the dorsum of the tongue, and supply the mucous membrane in this
situation, the glossopalatine arch, the tonsil, soft palate, and epiglottis; anastomosing with the vessels of the opposite side.
The Sublingual Artery (a. sublingualis) arises at the anterior margin of the Hyoglossus, and runs forward between
the Genioglossus and Mylohyoideus to the sublingual gland. It supplies the gland and gives branches to the Mylohyoideus
and neighboring muscles, and to the mucous membrane of the mouth and gums. One branch runs behind the alveolar process of the mandible in the substance of the gum to anastomose with a similar artery from the other side; another pierces the
Mylohyoideus and anastomoses with the submental branch of the external maxillary artery.
The Arteria Profunda Linguae (ranine artery; deep lingual artery) is the terminal portion of the lingual artery; it
pursues a tortuous course and runs along the under surface of the tongue, below the Longitudinalis inferior, and above the
mucous membrane; it lies on the lateral side of the Genioglossus, accompanied by the lingual nerve. At the tip of the
tongue, it is said to anastomose with the artery of the opposite side, but this is denied by Hyrtl. In the mouth, these vessels
are placed one on either side of the frenulum linguae.
3. The external maxillary artery (a. maxillaris externa; facial artery), arises in the carotid triangle a little above
the lingual artery and, sheltered by the ramus of the mandible, passes obliquely up beneath the Digastricus and Stylohyoideus, over which it arches to enter a groove on the posterior surface of the submaxillary gland. It then curves upward over
the body of the mandible at the antero-inferior angle of the Masseter; passes forward and upward across the cheek to the
angle of the mouth, then ascends along the side of the nose, and ends at the medial commissure of the eye, under the name
of the angular artery. This vessel, both in the neck and on the face, is remarkably tortuous: in the former situation, to accommodate itself to the movements of the pharynx in deglutition; and in the latter, to the movements of the mandible, lips,
and cheeks.
Relations.—In the neck, its origin is superficial, being covered by the integument, Platysma, and fascia; it then
passes beneath the Digastricus and Stylohyoideus muscles and part of the submaxillary gland, and frequently beneath the
hypoglossal nerve. It lies upon the Constrictores pharyngis medius and superior, the latter of which separates it, at the
summit of its arch, from the lower and back part of the tonsil. On the face, where it passes over the body of the mandible, it
is comparatively superficial, lying immediately beneath the Platysma. In its course over the face, it is covered by the integument, the fat of the cheek, and, near the angle of the mouth, by the Platysma, Risorius, and Zygomaticus. It rests on the
Buccinator and Caninus, and passes either over or under the infraorbital head of the Quadratus labii superioris. The anterior
facial vein lies lateral to the artery, and takes a more direct course across the face, where it is separated from the artery by a
considerable interval. In the neck it lies superficial to the artery. The branches of the facial nerve cross the artery from behind forward.
Branches.—The branches of the artery may be divided into two sets: those given off in the neck (cervical), and
those on the face (facial).
Cervical Branches – Ascending Palatine, Tonsillar, Glandular, Submental, Muscular.
Facial Branches – Inferior Labial, Superior Labial, Lateral Nasal, Angular, Muscular.
The Ascending Palatine Artery (a. palatina ascendens) arises close to the origin of the external maxillary artery
and passes up between the Styloglossus and Stylopharyngeus to the side of the pharynx, along which it is continued between the Constrictor pharyngis superior and the Pterygoideus internus to near the base of the skull. It divides near the Levator veli palatini into two branches: one follows the course of this muscle, and, winding over the upper border of the Constrictor pharyngis superior, supplies the soft palate and the palatine glands, anastomosing with its fellow of the opposite
side and with the descending palatine branch of the internal maxillary artery; the other pierces the Constrictor pharyngis
superior and supplies the palatine tonsil and auditory tube, anastomosing with the tonsillar and ascending pharyngeal arteries.
The Tonsillar Branch (ramus tonsillaris) ascends between the Pterygoideus internus and Styloglossus, and then
along the side of the pharynx, perforating the Constrictor pharyngis superior, to ramify in the substance of the palatine tonsil and root of the tongue.
The Glandular Branches (rami glandulares; submaxillary branches) consist of three or four large vessels, which
supply the submaxillary gland, some being prolonged to the neighboring muscles, lymph glands, and integument.
The Submental Artery (a. submentalis) the largest of the cervical branches, is given off from the facial artery just
as that vessel quits the submaxillary gland: it runs forward upon the Mylohyoideus, just below the body of the mandible,
and beneath the Digastricus. It supplies the surrounding muscles, and anastomoses with the sublingual artery and with the
mylohyoid branch of the inferior alveolar; at the symphysis menti it turns upward over the border of the mandible and divides into a superficial and a deep branch. The superficial branch passes between the integument and Quadratus labii inferioris, and anastomoses with the inferior labial artery; the deep branch runs between the muscle and the bone, supplies the
lip, and anastomoses with the inferior labial and mental arteries.
The Inferior Labial Artery (a. labialis inferior; inferior coronary artery) arises near the angle of the mouth; it
passes upward and forward beneath the Triangularis and, penetrating the Orbicularis oris, runs in a tortuous course along
the edge of the lower lip between this muscle and the mucous membrane. It supplies the labial glands, the mucous membrane, and the muscles of the lower lip; and anastomoses with the artery of the opposite side, and with the mental branch of
the inferior alveolar artery.
The Superior Labial Artery (a. labialis superior; superior coronary artery) is larger and more tortuous than the inferior. It follows a similar course along the edge of the upper lip, lying between the mucous membrane and the Orbicularis
oris, and anastomoses with the artery of the opposite side. It supplies the upper lip, and gives off in its course two or three
vessels which ascend to the nose; a septal branch ramifies on the nasal septum as far as the point of the nose, and an alar
branch supplies the ala of the nose.
The Lateral Nasal branch is derived from the external maxillary as that vessel ascends along the side of the nose. It
supplies the ala and dorsum of the nose, anastomosing with its fellow, with the septal and alar branches, with the dorsal
nasal branch of the ophthalmic, and with the infraorbital branch of the internal maxillary.
The Angular Artery (a. angularis) is the terminal part of the external maxillary; it ascends to the medial angle of
the orbit, imbedded in the fibers of the angular head of the Quadratus labii superioris, and accompanied by the angular vein.
On the cheek it distributes branches which anastomose with the infraorbital; after supplying the lacrimal sac and Orbicularis oculi, it ends by anastomosing with the dorsal nasal branch of the ophthalmic artery.
The Muscular Branches in the neck are distributed to the Pterygoideus internus and Stylohyoideus, and on the face
to the Masseter and Buccinator. The anastomoses of the external maxillary artery are very numerous, not only with the vessel of the opposite side, but, in the neck, with the sublingual branch of the lingual, with the ascending pharyngeal, and by its
ascending palatine and tonsillar branches with the palatine branch of the internal maxillary; on the face, with the mental
branch of the inferior alveolar as it emerges from the mental foramen, with the transverse facial branch of the superficial
temporal, with the infraorbital branch of the internal maxillary, and with the dorsal nasal branch of the ophthalmic.
Peculiarities.—The external maxillary artery not infrequently arises in common with the lingual. It varies in its size
and in the extent to which it supplies the face; it occasionally ends as the submental, and not infrequently extends only as
high as the angle of the mouth or nose. The deficiency is then compensated for by enlargement of one of the neighboring
arteries.
4. The occipital artery (a. occipitalis) arises from the posterior part of the external carotid, opposite the external
maxillary, near the lower margin of the posterior belly of the Digastricus, and ends in the posterior part of the scalp.
Course and Relations.—At its origin, it is covered by the posterior belly of the Digastricus and the Stylohyoideus,
and the hypoglossal nerve winds around it from behind forward; higher up, it crosses the internal carotid artery, the internal
jugular vein, and the vagus and accessory nerves. It next ascends to the interval between the transverse process of the atlas
and the mastoid process of the temporal bone, and passes horizontally backward, grooving the surface of the latter bone,
being covered by the Sternocleidomastoideus, Splenius capitis, Longissimus capitis, and Digastricus, and resting upon the
Rectus capitis lateralis, the Obliquus superior, and Semispinalis capitis. It then changes its course and runs vertically upward, pierces the fascia connecting the cranial attachment of the Trapezius with the Sternocleidomastoideus, and ascends in
a tortuous course in the superficial fascia of the scalp, where it divides into numerous branches, which reach as high as the
vertex of the skull and anastomose with the posterior auricular and superficial temporal arteries. Its terminal portion is accompanied by the greater occipital nerve.
Branches.—The branches of the occipital artery are: Muscular. Sternocleidomastoid. Auricular. Meningeal. Descending.
The Muscular Branches (rami musculares) supply the Digastricus, Stylohyoideus, Splenius, and Longissimus capitis.
The Sternocleidomastoid Artery (a. sternocleidomastoidea; sternomastoid artery) generally arises from the occipital close to its commencement, but sometimes springs directly from the external carotid. It passes downward and backward
over the hypoglossal nerve, and enters the substance of the muscle, in company with the accessory nerve.
The Auricular Branch (ramus auricularis) supplies the back of the concha and frequently gives off a branch, which
enters the skull through the mastoid foramen and supplies the dura mater, the diploë, and the mastoid cells; this latter
branch sometimes arises from the occipital artery, and is then known as the mastoid branch.
The Meningeal Branch (ramus meningeus; dural branch) ascends with the internal jugular vein, and enters the
skull through the jugular foramen and condyloid canal, to supply the dura mater in the posterior fossa.
The Descending Branch (ramus descendens; arteria princeps cervicis), the largest branch of the occipital, descends
on the back of the neck, and divides into a superficial and deep portion. The superficial portion runs beneath the Splenius,
giving off branches which pierce that muscle to supply the Trapezius and anastomose with the ascending branch of the
transverse cervical: the deep portion runs down between the Semispinales capitis and colli, and anastomoses with the vertebral and with the a. profunda cervicalis, a branch of the costocervical trunk. The anastomosis between these vessels assists
in establishing the collateral circulation after ligature of the common carotid or subclavian artery.
The terminal branches of the occipital artery are distributed to the back of the head: they are very tortuous, and lie
between the integument and Occipitalis, anastomosing with the artery of the opposite side and with the posterior auricular
and temporal arteries, and supplying the Occipitalis, the integument, and pericranium. One of the terminal branches may
give off a meningeal twig which passes through the parietal foramen.
5. The posterior auricular artery (a. auricularis posterior) is small and arises from the external carotid, above the
Digastricus and Stylohyoideus, opposite the apex of the styloid process. It ascends, under cover of the parotid gland, on the
styloid process of the temporal bone, to the groove between the cartilage of the ear and the mastoid process, immediately
above which it divides into its auricular and occipital branches.
Branches.—Besides several small branches to the Digastricus, Stylohyoideus, and Sternocleidomastoideus, and to
the parotid gland, this vessel gives off three branches: Stylomastoid. Auricular. Occipital.
The Stylomastoid Artery (a. stylomastoidea) enters the stylomastoid foramen and supplies the tympanic cavity, the
tympanic antrum and mastoid cells, and the semicircular canals. In the young subject a branch from this vessel forms, with
the anterior tympanic artery from the internal maxillary, a vascular circle, which surrounds the tympanic membrane, and
from which delicate vessels ramify on that membrane. It anastomoses with the superficial petrosal branch of the middle
meningeal artery by a twig which enters the hiatus canalis facialis.
The Auricular Branch (ramus auricularis) ascends behind the ear, beneath the Auricularis posterior, and is distributed to the back of the auricula, upon which it ramifies minutely, some branches curving around the margin of the cartilage,
others perforating it, to supply the anterior surface. It anastomoses with the parietal and anterior auricular branches of the
superficial temporal.
The Occipital Branch (ramus occipitalis) passes backward, over the Sternocleidomastoideus, to the scalp above
and behind the ear. It supplies the Occipitalis and the scalp in this situation and anastomoses with the occipital artery.
6. The ascending pharyngeal artery (a. pharyngea ascendens), the smallest branch of the external carotid, is a
long, slender vessel, deeply seated in the neck, beneath the other branches of the external carotid and under the Stylopharyngeus. It arises from the back part of the external carotid, near the commencement of that vessel, and ascends vertically
between the internal carotid and the side of the pharynx, to the under surface of the base of the skull, lying on the Longus
capitis.
Branches.—Its branches are: Pharyngeal. Prevertebral. Palatine. Inferior Tympanic. Posterior Meningeal.
The Pharyngeal Branches (rami pharyngei) are three or four in number. Two of these descend to supply the Constrictores pharyngis medius and inferior and the Stylopharyngeus, ramifying in their substance and in the mucous membrane lining them.
The Palatine Branch varies in size, and may take the place of the ascending palatine branch of the facial artery,
when that vessel is small. It passes inward upon the Constrictor pharyngis superior, sends ramifications to the soft palate
and tonsil, and supplies a branch to the auditory tube.
The Prevertebral Branches are numerous small vessels, which supply the Longi capitis and colli, the sympathetic
trunk, the hypoglossal and vagus nerves, and the lymph glands; they anastomose with the ascending cervical artery.
The Inferior Tympanic Artery (a. tympanica inferior) is a small branch which passes through a minute foramen in
the petrous portion of the temporal bone, in company with the tympanic branch of the glossopharyngeal nerve, to supply
the medial wall of the tympanic cavity and anastomose with the other tympanic arteries.
The Meningeal Branches are several small vessels, which supply the dura mater. One, the posterior meningeal,
enters the cranium through the jugular foramen; a second passes through the foramen lacerum; and occasionally a third
through the canal for the hypoglossal nerve.
7. The superficial temporal artery (a. temporalis superficialis), the smaller of the two terminal branches of the external carotid, appears, from its direction, to be the continuation of that vessel. It begins in the substance of the parotid
gland, behind the neck of the mandible, and corsses over the posterior root of the zygomatic process of the temporal bone;
about 5 cm. above this process it divides into two branches, a frontal and a parietal.
Relations.—As it crosses the zygomatic process, it is covered by the Auricularis anterior muscle, and by a dense
fascia; it is crossed by the temporal and zygomatic branches of the facial nerve and one or two veins, and is accompanied
by the auriculotemporal nerve, which lies immediately behind it.
Branches.—Besides some twigs to the parotid gland, to the temporomandibular joint, and to the Masseter muscle,
its branches are: Transverse Facial. Anterior Auricular. Middle Temporal. Frontal. Parietal.
The Transverse Facial Artery (a. transversa faciei) is givien off from the superficial temporal before that vessel
quits the parotid gland; running forward through the substance of the gland, it passes transversely across the side of the
face, between the parotid duct and the lower border of the zygomatic arch, and divides into numerous branches, which supply the parotid gland and duct, the Masseter, and the integument, and anastomose with the external maxillary, masseteric,
buccinator, and infraorbital arteries. This vessel rests on the Masseter, and is accompanied by one or two branches of the
facial nerve.
The Middle Temporal Artery (a. temporalis media) arises immediately above the zygomatic arch, and, perforating
the temporal fascia, gives branches to the Temporalis, anastomosing with the deep temporal branches of the internal maxillary. It occasionally gives off a zygomaticoörbital branch, which runs along the upper border of the zygomatic arch, between the two layers of the temporal fascia, to the lateral angle of the orbit. This branch, which may arise directly from the
superficial temporal artery, supplies the Orbicularis oculi, and anastomoses with the lacrimal and palpebral branches of the
ophthalmic artery.
The Anterior Auricular Branches (rami auriculares anteriores) are distributed to the anterior portion of the auricula, the lobule, and part of the external meatus, anastomosing with the posterior auricular.
The Frontal Branch (ramus frontalis; anterior temporal) runs tortuously upward and forward to the forehead, supplying the muscles, integument, and pericranium in this region, and anastomosing with the supraorbital and frontal arteries.
The Parietal Branch (ramus parietalis; posterior temporal) larger than the frontal, curves upward and backward on
the side of the head, lying superficial to the temporal fascia, and anastomosing with its fellow of the opposite side, and with
the posterior auricular and occipital arteries.
8. The internal maxillary artery (a. maxillaris interna), the larger of the two terminal branches of the external carotid, arises behind the neck of the mandible, and is at first imbedded in the substance of the parotid gland; it passes forward between the ramus of the mandible and the sphenomandibular ligament, and then runs, either superficial or deep to
the Pterygoideus externus, to the pterygopalatine fossa. It supplies the deep structures of the face, and may be divided into
mandibular, pterygoid, and pterygopalatine portions.
The first or mandibular portion passes horizontally forward, between the ramus of the mandible and the sphenomandibular ligament, where it lies parallel to and a little below the auriculotemporal nerve; it crosses the inferior alveolar
nerve, and runs along the lower border of the Pterygoideus externus.
The second or pterygoid portion runs obliquely forward and upward under cover of the ramus of the mandible and
insertion of the Temporalis, on the superficial (very frequently on the deep) surface of the Pterygoideus externus; it then
passes between the two heads of origin of this muscle and enters the fossa.
The third or pterygopalatine portion lies in the pterygopalatine fossa in relation with the sphenopalatine ganglion.
The branches of this vessel may be divided into three groups, corresponding with its three divisions.
Branches of the First or Mandibular Portions.
Anterior Tympanic. Middle Meningeal. Deep Auricular. Accessory Meningeal. Inferior Alveolar.
The Anterior Tympanic Artery (a. tympanica anterior; tympanic artery) passes upward behind the temporomandibular articulation, enters the tympanic cavity through the petrotympanic fissure, and ramifies upon the tympanic membrane, forming a vascular circle around the membrane with the stylomastoid branch of the posterior auricular, and anastomosing with the artery of the pterygoid canal and with the caroticotympanic branch from the internal carotid.
The Deep Auricular Artery (a. auricularis profunda) often arises in common with the preceding. It ascends in the
substance of the parotid gland, behind the temporomandibular articulation, pierces the cartilaginous or bony wall of the
external acoustic meatus, and supplies its cuticular lining and the outer surface of the tympanic membrane. It gives a branch
to the temporomandibular joint.
The Middle Meningeal Artery (a. meningea media; medidural artery) is the largest of the arteries which supply the
dura mater. It ascends between the sphenomandibular ligament and the Pterygoideus externus, and between the two roots of
the auriculotemporal nerve to the foramen spinosum of the sphenoid bone, through which it enters the cranium; it then runs
forward in a groove on the great wing of the sphenoid bone, and divides into two branches, anterior and posterior. The anterior branch, the larger, crosses the great wing of the sphenoid, reaches the groove, or canal, in the sphenoidal angle of
the parietal bone, and then divides into branches which spread out between the dura mater and internal surface of the cranium, some passing upward as far as the vertex, and others backward to the occipital region. The posterior branch curves
backward on the squama of the temporal bone, and, reaching the parietal some distance in front of its mastoid angle, divides into branches which supply the posterior part of the dura mater and cranium. The branches of the middle meningeal
artery are distributed partly to the dura mater, but chiefly to the bones; they anastomose with the arteries of the opposite
side, and with the anterior and posterior meningeal.
The middle meningeal on entering the cranium gives off the following branches: (1) Numerous small vessels supply
the semilunar ganglion and the dura mater in this situation. (2) A superficial petrosal branch enters the hiatus of the facial
canal, supplies the facial nerve, and anastomoses with the stylomastoid branch of the posterior auricular artery. (3) A superior tympanic artery runs in the canal for the Tensor tympani, and supplies this muscle and the lining membrane of the
canal. (4) Orbital branches pass through the superior orbital fissure or through separate canals in the great wing of the
sphenoid, to anastomose with the lacrimal or other branches of the ophthalmic artery. (5) Temporal branches pass through
foramina in the great wing of the sphenoid, and anastomose in the temporal fossa with the deep temporal arteries.
The Accessory Meningeal Branch (ramus meningeus accessorius; small meningeal or parvidural branch) is sometimes derived from the preceding. It enters the skull through the foramen ovale, and supplies the semilunar ganglion and
dura mater.
The Inferior Alveolar Artery (a. alveolaris inferior; inferior dental artery) descends with the inferior alveolar
nerve to the mandibular foramen on the medial surface of the ramus of the mandible. It runs along the mandibular canal in
the substance of the bone, accompanied by the nerve, and opposite the first premolar tooth divides into two branches, incisor and mental. The incisor branch is continued forward beneath the incisor teeth as far as the middle line, where it anastomoses with the artery of the opposite side; the mental branch escapes with the nerve at the mental foramen, supplies the
chin, and anastomoses with the submental and inferior labial arteries. Near its origin the inferior alveolar artery gives off a
lingual branch which descends with the lingual nerve and supplies the mucous membrane of the mouth. As the inferior
alveolar artery enters the foramen, it gives off a mylohyoid branch which runs in the mylohyoid groove, and ramifies on
the under surface of the Mylohyoideus. The inferior alveolar artery and its incisor branch during their course through the
substance of the bone give off a few twigs which are lost in the cancellous tissue, and a series of branches which correspond in number to the roots of the teeth: these enter the minute apertures at the extremities of the roots, and supply the
pulp of the teeth.
Branches of the Second or Pterygoid Portion.
Deep Temporal. Masseteric. Pterygoid. Buccinator.
The Deep Temporal Branches, two in number, anterior and posterior, ascend between the Temporalis and the
pericranium; they supply the muscle, and anastomose with the middle temporal artery; the anterior communicates with the
lacrimal artery by means of small branches which perforate the zygomatic bone and great wing of the sphenoid.
The Pterygoid Branches (rami pterygoidei), irregular in their number and origin, supply the Pterygoidei.
The Masseteric Artery (a. masseterica) is small and passes lateralward through the mandibular notch to the deep
surface of the Masseter. It supplies the muscle, and anastomoses with the masseteric branches of the external maxillary and
with the transverse facial artery.
The Buccinator Artery (a. buccinatoria; buccal artery) is small and runs obliquely forward, between the Pterygoideus internus and the insertion of the Temporalis, to the outer surface of the Buccinator, to which it is distributed, anastomosing with branches of the external maxillary and with the infraorbital.
Branches of the Third or Pterygopalatine Portion.
Posterior Superior Alveolar. Artery of the Pterygoid Canal. Infraorbital. Pharyngeal. Descending Palatine. Sphenopalatine.
The Posterior Superior Alveolar Artery (a. alveolaris superior posterior; alveolar or posterior dental artery) is
given off from the internal maxillary, frequently in conjunction with the infraorbital just as the trunk of the vessel is passing
into the pterygopalatine fossa. Descending upon the tuberosity of the maxilla, it divides into numerous branches, some of
which enter the alveolar canals, to supply the molar and premolar teeth and the lining of the maxillary sinus, while others
are continued forward on the alveolar process to supply the gums.
The Infraorbital Artery (a. infraorbitalis) appears, from its direction, to be the continuation of the trunk of the internal maxillary, but often arises in conjunction with the posterior superior alveolar. It runs along the infraorbital groove
and canal with the infraorbital nerve, and emerges on the face through the infraorbital foramen, beneath the infraorbital
head of the Quadratus labii superioris. While in the canal, it gives off (a) orbital branches which assist in supplying the
Rectus inferior and Obliquus inferior and the lacrimal sac, and (b) anterior superior alveolar branches which descend
through the anterior alveolar canals to supply the upper incisor and canine teeth and the mucous membrane of the maxillary
sinus. On the face, some branches pass upward to the medial angle of the orbit and the lacrimal sac, anastomosing with the
angular branch of the external maxillary artery; others run toward the nose, anastomosing with the dorsal nasal branch of
the ophthalmic; and others descend between the Quadratus labii superioris and the Caninus, and anastomose with the external maxillary, transverse facial, and buccinator arteries. The four remaining branches arise from that portion of the internal
maxillary which is contained in the pterygopalatine fossa.
The Descending Palatine Artery (a. palatina descendens) descends through the pterygopalatine canal with the anterior palatine branch of the sphenopalatine ganglion, and, emerging from the greater palatine foramen, runs forward in a
groove on the medial side of the alveolar border of the hard palate to the incisive canal; the terminal branch of the artery
passes upward through this canal to anastomose with the sphenopalatine artery. Branches are distributed to the gums, the
palatine glands, and the mucous membrane of the roof of the mouth; while in the pterygopalatine canal it gives off twigs
which descend in the lesser palatine canals to supply the soft palate and palatine tonsil, anastomosing with the ascending
palatine artery.
The Artery of the Pterygoid Canal (a. canalis pterygoidei; Vidian artery) passes backward along the pterygoid canal with the corresponding nerve. It is distributed to the upper part of the pharynx and to the auditory tube, sending into the
tympanic cavity a small branch which anastomoses with the other tympanic arteries.
The Pharyngeal Branch is very small; it runs backward through the pharyngeal canal with the pharyngeal nerve,
and is distributed to the upper part of the pharynx and to the auditory tube.
The Sphenopalatine Artery (a. sphenopalatina; nasopalatine artery) passes through the sphenopalatine foramen
into the cavity of the nose, at the back part of the superior meatus. Here it gives off its posterior lateral nasal branches
which spread forward over the conchae and meatuses, anastomose with the ethmoidal arteries and the nasal branches of the
descending palatine, and assist in supplying the frontal, maxillary, ethmoidal, and sphenoidal sinuses. Crossing the under
surface of the sphenoid the sphenopalatine artery ends on the nasal septum as the posterior septal branches; these anastomose with the ethmoidal arteries and the septal branch of the superior labial; one branch descends in a groove on the vomer to the incisive canal and anastomoses with the descending palatine artery.
Practice skills
Students are supposed to identify the following structures on the samples:
External carotid artery
- ascending pharyngeal artery
- superior thyroid artery
- superficial temporal artery
- lingual artery
- maxillary artery
- facial artery
- inferior alveolar artery
- occipital artery
- middle meningeal artery
- posterior auricular artery
Practice class 16. The innervation and blood supplement of the organs and cavities of the head
and neck. The regional lymphatic nodes and vessels of the neck and head. Examination of selftaught tasks. Tutorial of module 2.
The aim: to learn the nerve and blood supply of the cavities and organs of head and neck; to learn the regional lymph nodes and vessels of head and neck.
Professional orientation: the knowledge of this topic is necessary for doctors of all specialities; it represents special interest for therapists, surgeons and others.
The plan of the practice class:
A. Checking of the home assignment: oral quiz or written test control – 30 minutes.
B. Summary lecture on the topic by teacher – 30 minutes.
a) The lymphatics of the head and face.
b) The lymphatics of the neck.
c) Nerve and vessel supply of the head and neck.
C. Students’ self-taught time – 55 minutes
D. Home-task – 5 minutes
The Lymphatics of the Head, Face, and Neck
The Lymph Glands of the Head
The lymph glands of the head are arranged in the following groups:
Occipital. Facial. Posterior Auricular. Deep Facial. Anterior Auricular. Lingual. Parotid. Retropharyngeal.
The occipital glands (lymphoglandulae occipitales), one to three in nu ber, are placed on the back of the head close
to the margin of the Trapezius and resting on the insertion of the Semispinalis capitis. Their afferent vessels drain the occipital region of the scalp, while their efferents pass to the superior deep cervical glands.
The posterior auricular glands (lymphoglandulae auriculares; mastoid glands), usually two in number, are situated on the mastoid insertion of the Sternocleidomastoideus, beneath the Auricularis posterior. Their afferent vessels drain
the posterior part of the temporoparietal region, the upper part of the cranial surface of the auricula or pinna, and the back
of the external acoustic meatus; their efferents pass to the superior deep cervical glands.
The anterior auricular glands (lymphoglandulae auriculares anteriores; superficial parotid or preauricular
glands), from one to three in number, lie immediately in front of the tragus. Their afferents drain the lateral surface of the
auricula and the skin of the adjacent part of the temporal region; their efferents pass to the superior deep cervical glands.
The parotid glands (lymphoglandulae parotideae), form two groups in relation with the parotid salivary gland, viz.,
a group imbedded in the substance of the gland, and a group of subparotid glands lying on the lateral wall of the pharynx.
Occasionally small glands are found in the subcutaneous tissue over the parotid gland. Their afferent vessels drain the root
of the nose, the eyelids, the frontotemporal region, the external acoustic meatus and the tympanic cavity, possibly also the
posterior parts of the palate and the floor of the nasal cavity. The efferents of these glands pass to the superior deep cervical
glands. The afferents of the subparotid glands drain the nasal part of the pharynx and the posterior parts of the nasal cavities; their efferents pass to the superior deep cervical glands.
The facial glands comprise three groups: (a) infraorbital or maxillary, scattered over the infraorbital region from
the groove between the nose and cheek to the zygomatic arch; (b) buccinator, one or more placed on the Buccinator opposite the angle of the mouth; (c) supramandibular, on the outer surface of the mandible, in front of the Masseter and in
contact with the external maxillary artery and anterior facial vein. Their efferent vessels drain the eyelids, the conjunctiva,
and the skin and mucous membrane of the nose and cheek; their efferents pass to the submaxillary glands.
The deep facial glands (lymphoglandulae faciales profunda; internal maxillary glands) are placed beneath the ramus of the mandible, on the outer surface of the Pterygoideus externus, in relation to the internal maxillary artery. Their
afferent vessels drain the temporal and infratemporal fossae and the nasal part of the pharynx their efferents pass to the superior deep cervical glands.
The lingual glands (lymphoglandulae linguales) are two or three small nodules lying on the Hyoglossus and under
the Genioglossus. They form merely glandular substations in the course of the lymphatic vessels of the tongue.
The retropharyngeal glands, from one to three in number, lie in the buccopharyngeal fascia, behind the upper part
of the pharynx and in front of the arch of the atlas, being separated, however, from the latter by the Longus capitis. Their
afferents drain the nasal cavities, the nasal part of the pharynx, and the auditory tubes; their efferents pass to the superior
deep cervical glands.
The lymphatic vessels of the scalp are divisible into (a) those of the frontal region, which terminate in the anterior
auricular and parotid glands; (b) those of the temporoparietal region, which end in the parotid and posterior auricular
glands; and (c) those of the occipital region, which terminate partly in the occipital glands and partly in a trunk which runs
down along the posterior border of the Sternocleidomastoideus to end in the inferior deep cervical glands.
The lymphatic vessels of the auricula and external acoustic meatus are also divisible into three groups: (a) an anterior, from the lateral surface of the auricula and anterior wall of the meatus to the anterior auricular glands; (b) a posterior, from the margin of the auricula, the upper part of its cranial surface, the internal surface and posterior wall of the meatus
to the posterior auricular and superior deep cervical glands; (c) an inferior, from the floor of the meatus and from the lobule
of the auricula to the superficial and superior deep cervical glands.
The lymphatic vessels of the face are more numerous than those of the scalp. Those from the eyelids and conjunctiva terminate partly in the submaxillary but mainly in the parotid glands. The vessels from the posterior part of the cheek
also pass to the parotid glands, while those from the anterior portion of the cheek, the side of the nose, the upper lip, and the
lateral portions of the lower lip end in the submaxillary glands. The deeper vessels from the temporal and infratemporal
fossae pass to the deep facial and superior deep cervical glands. The deeper vessels of the cheek and lips end, like the su-
perficial, in the submaxillary glands. Both superficial and deep vessels of the central part of the lower lip run to the submental glands.
Lymphatic Vessels of the Nasal Cavities.—Those from the anterior parts of the nasal cavities communicate with
the vessels of the integument of the nose and end in the submaxillary glands; those from the posterior two-thirds of the nasal cavities and from the accessory air sinuses pass partly to the retropharyngeal and partly to the superior deep cervical
glands.
Lymphatic Vessels of the Mouth.—The vessels of the gums pass to the submaxillary glands; those of the hard palate are continuous in front with those of the upper gum, but pass backward to pierce the Constrictor pharyngis superior and
end in the superior deep cervical and subparotid glands; those of the soft palate pass backward and lateralward and end
partly in the retropharyngeal and subparotid, and partly in the superior deep cervical glands. The vessels of the anterior part
of the floor of the mouth pass either directly to the inferior glands of the superior deep cervical group, or indirectly through
the submental glands; from the rest of the floor of the mouth the vessels pass to the submaxillary and superior deep cervical
glands.
The lymphatic vessels of the palatine tonsil, usually three to five in number, pierce the buccopharyngeal fascia and
constrictor pharyngis superior and pass between the Stylohyoideus and internal jugular vein to the uppermost of the superior deep cervical glands. They end in a gland which lies at the side of the posterior belly of the Digastricus, on the internal
jugular vein; occasionally one or two additional vessels run to small glands on the lateral side of the vein under cover of the
Sternocleidomastoideus
The lymphatic vessels of the tongue are drained chiefly into the deep cervical glands lying between the posterior
belly of the Digastricus and the superior belly of the Omohyoideus; one gland situated at the bifurcation of the common
carotid artery is so intimately associated with these vessels that it is known as the principal gland of the tongue. The lymphatic vessels of the tongue may be divided into four groups: (1) apical, from the tip of the tongue to the suprahyoid glands
and principal gland of the tongue; (2) lateral, from the margin of the tongue—some of these pierce the Mylohyoideus to
end in the submaxillary glands, others pass down on the Hyoglossus to the superior deep cervical glands; (3) basal, from
the region of the vallate papillae to the superior deep cervical glands; and (4) median, a few of which perforate the Mylohyoideus to reach the submaxillary glands, while the majority turn around the posterior border of the muscle to enter the
superior deep cervical glands.
The Lymph Glands of the Neck—The lymph glands of the neck include the following groups:
Submaxillary. Superficial Cervical. Submental. Anterior Cervical. Deep Cervical.
The submaxillary glands (lymphoglandulae submaxillares), three to six in number, are placed beneath the body of
the mandible in the submaxillary triangle, and rest on the superficial surface of the submaxillary salivary gland. One gland,
the middle gland of Stahr, which lies on the external maxillary artery as it turns over the mandible, is the most constant of
the series; small lymph glands are sometimes found on the deep surface of the submaxillary salivary glands. The afferents
of the submaxillary glands drain the medial palpebral commissure, the cheek, the side of the nose, the upper lip, the lateral
part of the lower lip, the gums, and the anterior part of the margin of the tongue; efferent vessels from the facial and submental glands also enter the submaxillary glands. Their efferent vessels pass to the superior deep cervical glands.
The submental or suprahyoid glands are situated between the anterior bellies of the Digastrici. Their afferents
drain the central portions of the lower lip and floor of the mouth and the apex of the tongue; their efferents pass partly to
the submaxillary glands and partly to a gland of the deep cervical group situated on the internal jugular vein at the level of
the cricoid cartilage.
The superficial cervical glands (lymphoglandulae cervicales superficiales) lie in close relationship with the external jugular vein as it emerges from the parotid gland, and, therefore, superficial to the Sternocleidomastoideus. Their afferents drain the lower parts of the auricula and parotid region, while their efferents pass around the anterior margin of the
Sternocleidomastoideus to join the superior deep cervical glands.
The anterior cervical glands form an irregular and inconstant group on the front of the larynx and trachea. They
may be divided into (a) a superficial set, placed on the anterior jugular vein; (b) a deeper set, which is further subdivided
into prelaryngeal, on the middle cricothyroid ligament, and pretracheal, on the front of the trachea. This deeper set drains
the lower part of the larynx, the thyroid gland, and the upper part of the trachea; its efferents pass to the lowest of the superior deep cervical glands.
The deep cervical glands (lymphoglandulae cervicales profundae) (Figs. 602, 605) are numerous and of large size:
they form a chain along the carotid sheath, lying by the side of the pharynx, esophagus, and trachea, and extending from the
base of the skull to the root of the neck. They are usually described in two groups: (1) the superior deep cervical glands
lying under the Sternocleidomastoideus in close relation with the accessory nerve and the internal jugular vein, some of the
glands lying in front of and others behind the vessel; (2) the inferior deep cervical glands extending beyond the posterior
margin of the Sternocleidomastoideus into the supraclavicular triangle, where they are closely related to the brachial plexus
and subclavian vein. A few minute paratracheal glands are situated alongside the recurrent nerves on the lateral aspects of
the trachea and esophagus. The superior deep cervical glands drain the occipital portion of the scalp, the auricula, the back
of the neck, a considerable part of the tongue, the larynx, thyroid gland, trachea, nasal part of the pharynx, nasal cavities,
palate, and esophagus. They receive also the efferent vessels from all the other glands of the head and neck, except those
from the inferior deep cervical glands. The inferior deep cervical glands drain the back of the scalp and neck, the superficial
pectoral region, part of the arm, and, occasionally, part of the superior surface of the liver, In addition, they receive vessels
from the superior deep cervical glands. The efferents of the superior deep cervical glands pass partly to the inferior deep
cervical glands and partly to a trunk which unites with the efferent vessel of the inferior deep cervical glands and forms the
jugular trunk. On the right side, this trunk ends in the junction of the internal jugular and subclavian veins; on the left side
it joins the thoracic duct.
Self-taught class 11. The arteries of the orbit, nasal and oral cavity.
The aim: to learn the arteries of the orbit, nasal and oral cavities.
Professional orientation: the knowledge of this topic is necessary for doctors of all specialities; it represents special interest for therapists.
The plan of the self-taught class:
A. Revise the structures composing the walls of the orbit, nasal and oral cavities, and organs of these cavities.
B. Find out the branches of the internal carotid artery supplying the organs of the orbit.
C. Find out the anastomoses between the branches of external and internal carotid arteries around the orbit.
D. Learn the branches of the external and internal carotid arteries supplying the nasal cavity.
E. Learn the branches of the external and internal carotid arteries supplying the oral cavity.
F. Learn the branches of the external carotid artery supplying the oral cavity.
For more information see practice classes 13 (The internal carotid arteries: relations, anastomoses,
branches), 15 (The external carotid arteries: relations, anastomoses, branches, supplement. The innervation and
blood supplement of the nasal cavity), 16 (The innervation and blood supplement of the organs and cavities of
the head and neck)
Self-taught class 12. The arteries and veins of the cranial cavity.
The aim: to learn the arteries and veins of the cranial cavity.
Professional orientation: the knowledge of this topic is necessary for doctors of all specialities; it represents special interest for therapists.
The plan of the self-taught class:
A. Revise the structures composing the anterior, median and posterior cranial fossae.
B. Revise the structures which serve for communication of the cranial fossae with other cavities and structures
of the skull.
C. Learn the vessel supply of the anterior cranial fossa.
D. Learn the vessel supply of the median cranial fossa.
E. Learn the vessel supply of the posterior cranial fossa.
F. Revise the sinuses of cranial dura mater.
G. Learn the blood drainage from the cranial cavity (sinuses of the cranial dura mater, diploic veins, emissary
veins).
The Sinuses of the Dura Mater (Sinus Durae Matris). Ophthalmic Veins and Emissary Veins
The sinuses of the dura mater are venous channels which drain the blood from the brain; they are devoid of valves,
and are situated between the two layers of the dura mater and lined by endothelium continuous with that which lines the
veins. They may be divided into two groups: (1) a postero-superior, at the upper and back part of the skull, and (2) an antero-inferior, at the base of the skull.
The postero-superior group comprises the
Superior Sagittal. Inferior Sagittal. Straight. Two Transverse. Occipital.
The superior sagittal sinus (sinus sagittalis superior; superior longitudinal sinus) occupies the attached or convex
margin of the falx cerebri. Commencing at the foramen cecum, through which it receives a vein from the nasal cavity, it
runs from before backward, grooving the inner surface of the frontal, the adjacent margins of the two parietals, and the superior division of the cruciate eminence of the occipital; near the internal occipital protuberance it deviates to one or other
side (usually the right), and is continued as the corresponding transverse sinus. It is triangular in section, narrow in front,
and gradually increases in size as it passes backward. Its inner surface presents the openings of the superior cerebral veins,
which run, for the most part, obliquely forward, and open chiefly at the back part of the sinus, their orifices being concealed
by fibrous folds; numerous fibrous bands (chordae Willisii) extend transversely across the inferior angle of the sinus; and,
lastly, small openings communicate with irregularly shaped venous spaces (venous lacunae) in the dura mater near the sinus. There are usually three lacunae on either side of the sinus: a small frontal, a large parietal, and an occipital, intermediate in size between the other two. Most of the cerebral veins from the outer surface of the hemisphere open into these lacunae, and numerous arachnoid granulations (Pacchionian bodies) project into them from below. The superior sagittal sinus
receives the superior cerebral veins, veins from the diploë and dura mater, and, near the posterior extremity of the sagittal
suture, veins from the pericranium, which pass through the parietal foramina.
The numerous communications exist between this sinus and the veins of the nose, scalp, and diploë.
The inferior sagittal sinus (sinus sagittalis inferior; inferior longitudinal sinus) is contained in the posterior half or
two-thirds of the free margin of the falx cerebri. It is of a cylindrical form, increases in size as it passes backward, and ends
in the straight sinus. It receives several veins from the falx cerebri, and occasionally a few from the medial surfaces of the
hemispheres.
The straight sinus (sinus rectus; tentorial sinus) is situated at the line of junction of the falx cerebri with the tentorium cerebelli. It is triangular in section, increases in size as it proceeds backward, and runs downward and backward from
the end of the inferior sagittal sinus to the transverse sinus of the opposite side to that into which the superior sagittal sinus
is prolonged. Its terminal part communicates by a cross branch with the confluence of the sinuses. Besides the inferior sagittal sinus, it receives the great cerebral vein (great vein of Galen) and the superior cerebellar veins. A few transverse bands
cross its interior.
The transverse sinuses (sinus transversus; lateral sinuses) are of large size and begin at the internal occipital protuberance; one, generally the right, being the direct continuation of the superior sagittal sinus, the other of the straight sinus.
Each transverse sinus passes lateralward and forward, describing a slight curve with its convexity upward, to the base of the
petrous portion of the temporal bone, and lies, in this part of its course, in the attached margin of the tentorium cerebelli; it
then leaves the tentorium and curves downward and medialward to reach the jugular foramen, where it ends in the internal
jugular vein. In its course it rests upon the squama of the occipital, the mastoid angle of the parietal, the mastoid part of the
temporal, and, just before its termination, the jugular process of the occipital; the portion which occupies the groove on the
mastoid part of the temporal is sometimes termed the sigmoid sinus. The transverse sinuses are frequently of unequal size,
that formed by the superior sagittal sinus being the larger; they increase in size as they proceed from behind forward. On
transverse section the horizontal portion exhibits a prismatic, the curved portion a semicylindrical form. They receive the
blood from the superior petrosal sinuses at the base of the petrous portion of the temporal bone; they communicate with the
veins of the pericranium by means of the mastoid and condyloid emissary veins; and they receive some of the inferior cerebral and inferior cerebellar veins, and some veins from the diploë. The petrosquamous sinus, when present, runs backward
along the junction of the squama and petrous portion of the temporal, and opens into the transverse sinus.
The occipital sinus (sinus occipitalis) is the smallest of the cranial sinuses. It is situated in the attached margin of the
falx cerebelli, and is generally single, but occasionally there are two. It commences around the margin of the foramen magnum by several small venous channels, one of which joins the terminal part of the transverse sinus; it communicates with
the posterior internal vertebral venous plexuses and ends in the confluence of the sinuses.
The Confluence of the Sinuses (confluens sinuum; torcular Herophili) is the term applied to the dilated extremity of
the superior sagittal sinus. It is of irregular form, and is lodged on one side (generally the right) of the internal occipital
protuberance. From it the transverse sinus of the same side is derived. It receives also the blood from the occipital sinus,
and is connected across the middle line with the commencement of the transverse sinus of the opposite side.
The antero-inferior group of sinuses comprises the
Two Cavernous. Two Intercavernous. Two Superior Petrosal. Two Inferior Petrosal. Basilar Plexus.
The cavernous sinuses (sinus cavernosus) are so named because they present a reticulated structure, due to their being traversed by numerous interlacing filaments. They are of irregular form, larger behind than in front, and are placed one
on either side of the body of the sphenoid bone, extending from the superior orbital fissure to the apex of the petrous portion of the temporal bone. Each opens behind into the petrosal sinuses. On the medial wall of each sinus is the internal carotid artery, accompanied by filaments of the carotid plexus; near the artery is the abducent nerve; on the lateral wall are the
oculomotor and trochlear nerves, and the ophthalmic and maxillary divisions of the trigeminal nerve. These structures are
separated from the blood flowing along the sinus by the lining membrane of the sinus. The cavernous sinus receives the
superior ophthalmic vein through the superior orbital fissure, some of the cerebral veins, and also the small sphenoparietal
sinus, which courses along the under surface of the small wing of the sphenoid. It communicates with the transverse sinus
by means of the superior petrosal sinus; with the internal jugular vein through the inferior petrosal sinus and a plexus of
veins on the internal carotid artery; with the pterygoid venous plexus through the foramen Vesalii, foramen ovale, and foramen lacerum, and with the angular vein through the ophthalmic vein. The two sinuses also communicate with each other
by means of the anterior and posterior intercavernous sinuses.
The ophthalmic veins, two in number, superior and inferior, are devoid of valves.
The Superior Ophthalmic Vein (v. ophthalmica superior) begins at the inner angle of the orbit in a vein named the
nasofrontal which communicates anteriorly with the angular vein; it pursues the same course as the ophthalmic artery, and
receives tributaries corresponding to the branches of that vessel. Forming a short single trunk, it passes between the two
heads of the Rectus lateralis and through the medial part of the superior orbital fissure, and ends in the cavernous sinus.
The Inferior Ophthalmic Vein (v. ophthalmica inferior) begins in a venous net-work at the forepart of the floor and
medial wall of the orbit; it receives some veins from the Rectus inferior, Obliquus inferior, lacrimal sac and eyelids, runs
backward in the lower part of the orbit and divides into two branches. One of these passes through the inferior orbital fissure and joins the pterygoid venous plexus, while the other enters the cranium through the superior orbital fissure and ends
in the cavernous sinus, either by a separate opening, or more frequently in common with the superior ophthalmic vein.
The intercavernous sinuses (sini intercavernosi) are two in number, an anterior and a posterior, and connect the two
cavernous sinuses across the middle line. The anterior passes in front of the hypophysis cerebri, the posterior behind it,
and they form with the cavernous sinuses a venous circle (circular sinus) around the hypophysis. The anterior one is usually the larger of the two, and one or other is occasionally absent.
The superior petrosal sinus (sinus petrosus superior) small and narrow, connects the cavernous with the transverse
sinus. It runs lateralward and backward, from the posterior end of the cavernous sinus, over the trigeminal nerve, and lies in
the attached margin of the tentorium cerebelli and in the superior petrosal sulcus of the temporal bone; it joins the transverse sinus where the latter curves downward on the inner surface of the mastoid part of the temporal. It receives some cerebellar and inferior cerebral veins, and veins from the tympanic cavity.
The inferior petrosal sinus (sinus petrosus inferior) is situated in the inferior petrosal sulcus formed by the junction
of the petrous part of the temporal with the basilar part of the occipital. It begins in the postero-inferior part of the cavernous sinus, and, passing through the anterior part of the jugular foramen, ends in the superior bulb of the internal jugular
vein. The inferior petrosal sinus receives the internal auditory veins and also veins from the medulla oblongata, pons, and
under surface of the cerebellum.
The exact relation of the parts to one another in the jugular foramen is as follows: the inferior petrosal sinus lies medially and anteriorly with the meningeal branch of the ascending pharyngeal artery, and is directed obliquely downward and
backward; the transverse sinus is situated at the lateral and back part of the foramen with a meningeal branch of the occipital artery, and between the two sinuses are the glossopharyngeal, vagus, and accessory nerves. These three sets of structures
are divided from each other by two processes of fibrous tissue. The junction of the inferior petrosal sinus with the internal
jugular vein takes place on the lateral aspect of the nerves.
The basilar plexus (plexus basilaris; transverse or basilar sinus) consists of several interlacing venous channels between the layers of the dura mater over the basilar part of the occipital bone, and serves to connect the two inferior petrosal
sinuses. It communicates with the anterior vertebral venous plexus.
Emissary Veins (emissaria).—The emissary veins pass through apertures in the cranial wall and establish communication between the sinuses inside the skull and the veins external to it. Some are always present, others only occasionally
so. The principal emissary veins are the following: (1) A mastoid emissary vein, usually present, runs through the mastoid
foramen and unites the transverse sinus with the posterior auricular or with the occipital vein. (2) A parietal emissary vein
passes through the parietal foramen and connects the superior sagittal sinus with the veins of the scalp. (3) A net-work of
minute veins (rete canalis hypoglossi) traverses the hypoglossal canal and joins the transverse sinus with the vertebral vein
and deep veins of the neck. (4) An inconstant condyloid emissary vein passes through the condyloid canal and connects the
transverse sinus with the deep veins of the neck. (5) A net-work of veins (rete foraminis ovalis) unites the cavernous sinus
with the pterygoid plexus through the foramen ovale. (6) Two or three small veins run through the foramen lacerum and
connect the cavernous sinus with the pterygoid plexus. (7) The emissary vein of the foramen of Vesalius connects the same
parts. (8) An internal carotid plexus of veins traverses the carotid canal and unites the cavernous sinus with the internal
jugular vein. (9) A vein is transmitted through the foramen cecum and connects the superior sagittal sinus with the veins of
the nasal cavity.
The Diploic Veins (Venae Diploicae)
The diploic veins occupy channels in the diploë of the cranial bones. They are large and exhibit at irregular intervals
pouch-like dilatations; their walls are thin, and formed of endothelium resting upon a layer of elastic tissue.
So long as the cranial bones are separable from one another, these veins are confined to the particular bones; but
when the sutures are obliterated, they unite with each other, and increase in size. They communicate with the meningeal
veins and the sinuses of the dura mater, and with the veins of the pericranium. They consist of (1) the frontal, which opens
into the supraorbital vein and the superior sagittal sinus; (2) the anterior temporal, which is confined chiefly to the frontal
bone, and opens into the sphenoparietal sinus and into one of the deep temporal veins, through an aperture in the great wing
of the sphenoid; (3) the posterior temporal, which is situated in the parietal bone, and ends in the transverse sinus, through
an aperture at the mastoid angle of the parietal bone or through the mastoid foramen; and (4) the occipital, the largest of the
four, which is confined to the occipital bone, and opens either externally into the occipital vein, or internally into the transverse sinus or into the confluence of the sinuses (torcular Herophili).
Practice skills
Students are supposed to identify the following structures on the samples:
- superior sagittal sinus
- confluens of sinuses
- inferior sagittal sinus
- sigmoid sinus
- straight sinus
- cavernous sinus
- occipital sinus
- superior petrosal sinus
- transverse sinus
- inferior petrosal sinus
Self-taught class 13. The veins of the head and neck. The veins of the brain.
The aim: to learn the veins of the head and neck; to learn the blood drainage from the brain.
Professional orientation: the knowledge of this topic is necessary for doctors of all specialities; it represents special interest for therapists.
The plan of the self-taught class:
A. Learn the tobography and tributarieis of the main veins of head and neck.
B. Learn the blood drainage from the brain.
The Veins of the Head and Neck
The veins of the head and neck may be subdivided into three groups: (1) The veins of the exterior of the head and
face. (2) The veins of the neck. (3) The diploic veins, the veins of the brain, and the venous sinuses of the dura mater.
The Veins of the Exterior of the Head and Face—The veins of the exterior of the head and face are:
Frontal. Superficial Temporal. Supraorbital. Internal Maxillary. Angular. Posterior Facial. Anterior Facial. Posterior
Auricular. Occipital.
The frontal vein (v. frontalis) begins on the forehead in a venous plexus which communicates with the frontal
branches of the superficial temporal vein. The veins converge to form a single trunk, which runs downward near the middle
line of the forehead parallel with the vein of the opposite side. The two veins are joined, at the root of the nose, by a transverse branch, called the nasal arch, which receives some small veins from the dorsum of the nose. At the root of the nose
the veins diverge, and, each at the medial angle of the orbit, joins the supraorbital vein, to form the angular vein. Occasionally the frontal veins join to form a single trunk, which bifurcates at the root of the nose into the two angular veins.
The supraorbital vein (v. supraorbitalis) begins on the forehead where it communicates with the frontal branch of
the superficial temporal vein. It runs downward superficial to the Frontalis muscle, and joins the frontal vein at the medial
angle of the orbit to form the angular vein. Previous to its junction with the frontal vein, it sends through the supraorbital
notch into the orbit a branch which communicates with the ophthalmic vein; as this vessel passes through the notch, it receives the frontal diploic vein through a foramen at the bottom of the notch.
The angular vein (v. angularis) formed by the junction of the frontal and supraorbital veins, runs obliquely downward, on the side of the root of the nose, to the level of the lower margin of the orbit, where it becomes the anterior facial
vein. It receives the veins of the ala nasi, and communicates with the superior ophthalmic vein through the nasofrontal vein,
thus establishing an important anastomosis between the anterior facial vein and the cavernous sinus.
The anterior facial vein (v. facialis anterior; facial vein) commences at the side of the root of the nose, and is a direct continuation of the angular vein. It lies behind the external maxillary (facial) artery and follows a less tortuous course.
It runs obliquely downward and backward, beneath the Zygomaticus and zygomatic head of the Quadratus labii superioris,
descends along the anterior border and then on the superficial surface of the Masseter, crosses over the body of the mandible, and passes obliquely backward, beneath the Platysma and cervical fascia, superficial to the submaxillary gland, the
Digastricus and Stylohyoideus. It unites with the posterior facial vein to form the common facial vein, which crosses the
external carotid artery and enters the internal jugular vein at a variable point below the hyoid bone. From near its termination a communicating branch often runs down the anterior border of the Sternocleidomastoideus to join the lower part of
the anterior jugular vein. The facial vein has no valves, and its walls are not so flaccid as most superficial veins.
Tributaries.—The anterior facial vein receives a branch of considerable size, the deep facial vein, from the pterygoid venous plexus. It is also joined by the superior and inferior palpebral, the superior and inferior labial, the buccinator
and the masseteric veins. Below the mandible it receives the submental, palatine, and submaxillary veins, and, generally,
the vena comitans of the hypoglossal nerve.
The superficial temporal vein (v. temporalis superficialis) begins on the side and vertex of the skull in a plexus
which communicates with the frontal and supraorbital veins, with the corresponding vein of the opposite side, and with the
posterior auricular and occipital veins. From this net-work frontal and parietal branches arise, and unite above the zygomatic arch to form the trunk of the vein, which is joined in this situation by the middle temporal vein, from the substance of
the Temporalis. It then crosses the posterior root of the zygomatic arch, enters the substance of the parotid gland, and unites
with the internal maxillary vein to form the posterior facial vein.
Tributaries.—The superficial temporal vein receives in its course some parotid veins, articular veins from the temporomandibular joint, anterior auricular veins from the auricula, and the transverse facial from the side of the face. The
middle temporal vein receives the orbital vein, which is formed by some lateral palpebral branches, and passes backward
between the layers of the temporal fascia to join the superficial temporal vein.
The pterygoid plexus (plexus pterygoideus) is of considerable size, and is situated between the Temporalis and
Pterygoideus externus, and partly between the two Pterygoidei. It receives tributaries corresponding with the branches of
the internal maxillary artery. Thus it receives the sphenopalatine, the middle meningeal, the deep temporal, the pterygoid,
masseteric, buccinator, alveolar, and some palatine veins, and a branch which communicates with the ophthalmic vein
through the inferior orbital fissure. This plexus communicates freely with the anterior facial vein; it also communicates
with the cavernous sinus, by branches through the foramen Vesalii, foramen ovale, and foramen lacerum.
The internal maxillary vein (v. maxillaris interna) is a short trunk which accompanies the first part of the internal
maxillary artery. It is formed by a confluence of the veins of the pterygoid plexus, and passes backward between the sphenomandibular ligament and the neck of the mandible, and unites with the temporal vein to form the posterior facial vein.
The posterior facial vein (v. facialis posterior; temporomaxillary vein), formed by the union of the superficial temporal and internal maxillary veins, descends in the substance of the parotid gland, superficial to the external carotid artery
but beneath the facial nerve, between the ramus of the mandible and the Sternocleidomastoideus muscle. It divides into two
branches, an anterior, which passes forward and unites with the anterior facial vein to form the common facial vein and a
posterior, which is joined by the posterior auricular vein and becomes the external jugular vein.
The posterior auricular vein (v. auricularis posterior) begins upon the side of the head, in a plexus which communicates with the tributaries of the occipital, and superficial temporal veins. It descends behind the auricula, and joins the
posterior division of the posterior facial vein to form the external jugular. It receive the stylomastoid vein, and some tributaries from the cranial surface of the auricula.
The occipital vein (v. occipitalis) begins in a plexus at the back part of the vertex of the skull, From the plexus
emerges a single vessel, which pierces the cranial attachment of the Trapezius and, dipping into the suboccipital triangle,
joins the deep cervical and vertebral veins. Occasionally it follows the course of the occipital artery and ends in the internal
jugular; in other instances, it joins the posterior auricular and through it opens into the external jugular. The parietal emissary vein connects it with the superior sagittal sinus; and as it passes across the mastoid portion of the temporal bone, it
receives the mastoid emissary vein which connects it with the transverse sinus. The occipital diploic vein sometimes joins
it.
The veins of the neck, which return the blood from the head and face, are:
External Jugular. Posterior External Jugular. Anterior Jugular. Internal Jugular. Vertebral.
The external jugular vein (v. jugularis externa) receives the greater part of the blood from the exterior of the cranium and the deep parts of the face, being formed by the junction of the posterior division of the posterior facial with the posterior auricular vein. It commences in the substance of the parotid gland, on a level with the angle of the mandible, and runs
perpendicularly down the neck, in the direction of a line drawn from the angle of the mandible to the middle of the clavicle
at the posterior border of the Sternocleidomastoideus. In its course it crosses the Sternocleidomastoideus obliquely, and in
the subclavian triangle perforates the deep fascia, and ends in the subclavian vein, lateral to or in front of the Scalenus anterior. It is separated from the Sternocleidomastoideus by the investing layer of the deep cervical fascia, and is covered by the
Platysma, the superficial fascia, and the integument; it crosses the cutaneous cervical nerve, and its upper half runs parallel
with the great auricular nerve. The external jugular vein varies in size, bearing an inverse proportion to the other veins of
the neck, it is occasionally double. It is provided with two pairs of valves, the lower pair being placed at its entrance into
the subclavian vein, the upper in most cases about 4 cm. above the clavicle. The portion of vein between the two sets of
valves is often dilated, and is termed the sinus. These valves do not prevent the regurgitation of the blood, or the passage of
injection from below upward.
Tributaries.—This vein receives the occipital occasionally, the posterior external jugular, and, near its termination,
the transverse cervical, transverse scapular, and anterior jugular veins; in the substance of the parotid, a large branch of
communication from the internal jugular joins it.
The posterior external jugular vein (v. jugularis posterior) begins in the occipital region and returns the blood
from the skin and superficial muscles in the upper and back part of the neck, lying between the Splenius and Trapezius. It
runs down the back part of the neck, and opens into the external jugular vein just below the middle of its course.
The anterior jugular vein (v. jugularis anterior) begins near the hyoid bone by the confluence of several superficial
veins from the submaxillary region. It descends between the median line and the anterior border of the Sternocleidomastoideus, and, at the lower part of the neck, passes beneath that muscle to open into the termination of the external jugular,
or, in some instances, into the subclavian vein. It varies considerably in size, bearing usually an inverse proportion to the
external jugular; most frequently there are two anterior jugulars, a right and left; but sometimes only one. Its tributaries are
some laryngeal veins, and occasionally a small thyroid vein. Just above the sternum the two anterior jugular veins communicate by a transverse trunk, the venous jugular arch, which receive tributaries from the inferior thyroid veins; each
also communicates with the internal jugular. There are no valves in this vein.
The internal jugular vein (v. jugularis interna) collects the blood from the brain, from the superficial parts of the
face, and from the neck. It is directly continuous with the transverse sinus, and begins in the posterior compartment of the
jugular foramen, at the base of the skull. At its origin it is somewhat dilated, and this dilatation is called the superior bulb.
It runs down the side of the neck in a vertical direction, lying at first lateral to the internal carotid artery, and then lateral to
the common carotid, and at the root of the neck unites with the subclavian vein to form the innominate vein; a little above
its termination is a second dilatation, the inferior bulb. Above, it lies upon the Rectus capitis lateralis, behind the internal
carotid artery and the nerves passing through the jugular foramen; lower down, the vein and artery lie upon the same plane,
the glossopharyngeal and hypoglossal nerves passing forward between them; the vagus descends between and behind the
vein and the artery in the same sheath, and the accessory runs obliquely backward, superficial or deep to the vein. At the
root of the neck the right internal jugular vein is placed at a little distance from the common carotid artery, and crosses the
first part of the subclavian artery, while the left internal jugular vein usually overlaps the common carotid artery. The left
vein is generally smaller than the right, and each contains a pair of valves, which are placed about 2.5 cm. above the termination of the vessel.
Tributaries.—This vein receives in its course the inferior petrosal sinus, the common facial, lingual, pharyngeal,
superior and middle thyroid veins, and sometimes the occipital. The thoracic duct on the left side and the right lymphatic
duct on the right side open into the angle of union of the internal jugular and subclavian veins.
The Inferior Petrosal Sinus (sinus petrosus inferior) leaves the skull through the anterior part of the jugular foramen, and joins the superior bulb of the internal jugular vein.
The Lingual Veins (vv. linguales) begin on the dorsum, sides, and under surface of the tongue, and, passing backward along the course of the lingual artery, end in the internal jugular vein. The vena comitans of the hypoglossal nerve
(ranine vein), a branch of considerable size, begins below the tip of the tongue, and may join the lingual; generally, however, it passes backward on the Hyoglossus, and joins the common facial.
The Pharyngeal Veins (vv. pharyngeae) begin in the pharyngeal plexus on the outer surface of the pharynx, and,
after receiving some posterior meningeal veins and the vein of the pterygoid canal, end in the internal jugular. They occasionally open into the facial, lingual, or superior thyroid vein.
The Superior Thyroid Vein (v. thyreoidea superioris) begins in the substance and on the surface of the thyroid
gland, by tributaries corresponding with the branches of the superior thyroid artery, and ends in the upper part of the internal jugular vein. It receives the superior laryngeal and cricothyroid veins.
The Middle Thyroid Vein collects the blood from the lower part of the thyroid gland, and after being joined by
some veins from the larynx and trachea, ends in the lower part of the internal jugular vein.
The common facial and occipital veins have been described.
The vertebral vein (v. vertebralis) is formed in the suboccipital triangle, from numerous small tributaries which
spring from the internal vertebral venous plexuses and issue from the vertebral canal above the posterior arch of the atlas.
They unite with small veins from the deep muscles at the upper part of the back of the neck, and form a vessel which enters
the foramen in the transverse process of the atlas, and descends, forming a dense plexus around the vertebral artery, in the
canal formed by the foramina transversaria of the cervical vertebrae. This plexus ends in a single trunk, which emerges
from the foramen transversarium of the sixth cervical vertebra, and opens at the root of the neck into the back part of the
innominate vein near its origin, its mouth being guarded by a pair of valves. On the right side, it crosses the first part of the
subclavian artery.
Tributaries.—The vertebral vein communicates with the transverse sinus by a vein which passes through the condyloid canal, when that canal exists. It receives branches from the occipital vein and from the prevertebral muscles, from
the internal and external vertebral venous plexuses, from the anterior vertebral and the deep cervical veins; close to its termination it is sometimes joined by the first intercostal vein.
The Anterior Vertebral Vein commences in a plexus around the transverse processes of the upper cervical vertebrae, descends in company with the ascending cervical artery between the Scalenus anterior and Longus capitis muscles,
and opens into the terminal part of the vertebral vein. The Deep Cervical Vein (v. cervicalis profunda; posterior vertebral
or posterior deep cervical vein) accompanies its artery between the Semispinales capitis and colli. It begins in the suboccipital region by communicating branches from the occipital vein and by small veins from the deep muscles at the back
of the neck. It receives tributaries from the plexuses around the spinous processes of the cervical vertebrae, and terminates
in the lower part of the vertebral vein.
The Veins of the Brain
The veins of the brain possess no valves, and their walls, owing to the absence of muscular tissue, are extremely
thin. They pierce the arachnoid membrane and the inner or meningeal layer of the dura mater, and open into the cranial
venous sinuses. They may be divided into two sets, cerebral and cerebellar.
The cerebral veins (vv. cerebri) are divisible into external and internal groups according as they drain the outer surfaces or the inner parts of the hemispheres.
The external veins are the superior, inferior, and middle cerebral.
The Superior Cerebral Veins (vv. cerebri superiores), eight to twelve in number, drain the superior, lateral, and
medial surfaces of the hemispheres, and are mainly lodged in the sulci between the gyri, but some run across the gyri. They
open into the superior sagittal sinus; the anterior veins runs nearly at right angles to the sinus; the posterior and larger veins
are directed obliquely forward and open into the sinus in a direction more or less opposed to the current of the blood contained within it.
The Middle Cerebral Vein (v. cerebri media; superficial Sylvian vein) begins on the lateral surface of the hemisphere, and, running along the lateral cerebral fissure, ends in the cavernous or the sphenoparietal sinus. It is connected (a)
with the superior sagittal sinus by the great anastomotic vein of Trolard, which opens into one of the superior cerebral
veins; (b) with the transverse sinus by the posterior anastomotic vein of Labbé, which courses over the temporal lobe.
The Inferior Cerebral Veins (vv. cerebri inferiores), of small size, drain the under surfaces of the hemispheres.
Those on the orbital surface of the frontal lobe join the superior cerebral veins, and through these open into the superior
sagittal sinus; those of the temporal lobe anastomose with the middle cerebral and basal veins, and join the cavernous,
sphenoparietal, and superior petrosal sinuses.
The basal vein is formed at the anterior perforated substance by the union of (a) a small anterior cerebral vein
which accompanies the anterior cerebral artery, (b) the deep middle cerebral vein (deep Sylvian vein), which receives
tributaries from the insula and neighboring gyri, and runs in the lower part of the lateral cerebral fissure, and (c) the inferior striate veins, which leave the corpus striatum through the anterior perforated substance. The basal vein passes backward
around the cerebral peduncle, and ends in the internal cerebral vein (vein of Galen); it receives tributaries from the interpeduncular fossa, the inferior horn of the lateral ventricle, the hippocampal gyrus, and the mid-brain.
The Internal Cerebral Veins (vv. cerebri internae; veins of Galen; deep cerebral veins) drain the deep parts of the
hemisphere and are two in number; each is formed near the interventricular foramen by the union of the terminal and choroid veins. They run backward parallel with one another, between the layers of the tela chorioidea of the third ventricle,
and beneath the splenium of the corpus callosum, where they unite to form a short trunk, the great cerebral vein; just before their union each receives the corresponding basal vein.
The terminal vein (v. terminalis; vena corporis striati) commences in the groove between the corpus striatum and
thalamus, receives numerous veins from both of these parts, and unites behind the crus fornicis with the choroid vein, to
form one of the internal cerebral veins. The choroid vein runs along the whole length of the choroid plexus, and receives
veins from the hippocampus, the fornix, and the corpus callosum.
The Great Cerebral Vein (v. cerebri magna [Galeni]; great vein of Galen), formed by the union of the two internal
cerebral veins, is a short median trunk which curves backward and upward around the splenium of the corpus callosum and
ends in the anterior extremity of the straight sinus.
The cerebellar veins are placed on the surface of the cerebellum, and are disposed in two sets, superior and inferior.
The superior cerebellar veins (vv. cerebelli superiores) pass partly forward and medialward, across the superior vermis, to
end in the straight sinus and the internal cerebral veins, partly lateralward to the transverse and superior petrosal sinuses.
The inferior cerebellar veins (vv. cerebelli inferiores) of large size, end in the transverse, superior petrosal, and occipital
sinuses.
Practice skills
Students are supposed to identify the following structures on the samples:
Internal jugular vein
- anterior jugular vein
- facial vein
Superior vena cava
- retromandibular vein
Brachiocephalic vein (right, left)
External jugular vein
Practice class 17. Examination of module 3.
Written tests of the vessels of head and neck
I. Tests of basic theory
1.
2.
3.
4.
5.
6.
7.
8.
9.
The aorta
A. becomes the descending aorta at TV4
B. enters the abdomen at TV 12
C. bifurcates into the common iliac arteries at LV4
D. b and c
E. *a, b and c
A patient with an aneurysm of the aortic arch develops hoarseness. Which of the following muscles on
the left is most likely to be paralyzed?
A. cricothyroid
B. sternothyroid
C. *posterior cricoarytenoid
D. a and c
E. none of the above
Which of the following are branches of the basilar
artery?
A. pontine arteries
B. superior cerebellar arteries
C. anterior inferior cerebellar arteries
D. posterior cerebral arteries
E. *all are branches
Infection can spread to and from the cavernous sinus
and the facial vein via:
A. ophthalmic veins
B. pterygoid plexus
C. deep facial vein
D. a and b
E. *a, b and c
Tears in the esophageal mucosa are found as a result
of prolonged vomiting. Which of the following arteries would NOT likely contribute to bleeding from
such a lesion?
A. inferior thyroid artery
B. esophageal branches from thoracic aorta
C. branches from bronchial arteries
D. branches from the left gastric artery
E. *the hepatic artery
Which artery lies on the anterior surface of the anterior scalene muscle?
A. superior thyroid artery
B. *ascending cervical artery
C. vertebral. artery
D. costocervical trunk
E. subclavian A
All of the following are branches of the maxillary
artery, EXCEPT:
A. anterior tympanic A
B. middle meningeal A
C. buccal A
D. *posterior auricular A
E. inferior alveolar A
A rhabdomyosarcoma (malignant striated muscle
tumor) involves the whole of the middle scalene
muscle. What structures will be affected by the tumor?
A. dorsal scapular nerve
B. long thoracic nerve
C. subclavian artery, if tumor extends anteriorly
D. a and c
E. *a, b and c
The subclavian artery passes
A. anterior to the phrenic nerve
B. anterior to the scalenus anterior muscle
10.
11.
12.
13.
14.
15.
16.
C. posterior to the lower trunk of the brachial
plexus
D. posterior to the scalenus medius muscle
E. *posterior to the vagus nerve
The ophthalmic artery:
A. arises from the internal carotid artery within the
middle cranial fossa
B. passes within the arachnoid and dural sheaths of
the optic nerve
C. leaves the middle cranial fossa by the optic canal and is inferior to the optic nerve
D. a and b
E. *a, b, and c
Which venous sinus drains the cavernous sinus directly into the internal jugular vein?
A. sigmoid sinus
B. straight sinus
C. transverse sinus
D. *inferior petrosal sinus
E. inferior sagittal sinus
A thrombus located in the left cavernous sinus impinging on all structures related to it would cause:
A. difficulty in moving the left eye in any direction
B. decreased sensation on the lateral wall of the
nasal cavity
C. decreased sensation surrounding the orbit
D. a dry eye due to decreased function of the lacrimal gland
E. *a, b, and c
The internal jugular vein:
A. arises from the sigmoid sinus
B. descends in the neck moving posterior to lateral
in relationship to the carotid artery
C. unites with the subclavian vein to form the. brachiocephalic vein
D. a and c
E. *a, b, and c
Before sticking a needle or catheter into the carotid
sheath, one should know which of the following relationships is TRUE:
A. the common carotid artery is lateral
B. *the internal jugular vein is lateral
C. The sympathetic trunk is central
D. the vagus nerve is anterior
E. all of the above are true
The esophagus:
A. is innervated by splanchnic nerves from the
sympathetic trunk carrying preganglionic fibers
B. *receives its blood supply in part from the inferior thyroid artery and a branch from the left
gastric artery
C. its immediate venous drainage is totally into the
vena caval system
D. begins at CV4
E. all of the above
The division of the aorta with the fewest branches is
normally the:
A. *ascending aorta
B. aortic arch
C. descending thoracic aorta
D. abdominal aorta
E. same number of branches in all aortic divisions
listed
17. All of the following arteries are branches of the external carotid, EXCEPT:
A. lingual A
B. *ascending cervical A
C. superior thyroid A
D. posterior auricular A
E. occipital A
18. The following statements about the superior vena
cava are true, EXCEPT:
A. It begins at the level of the right first costal cartilage.
B. It receives the right and left brachiocephalic and
the azygos veins.
C. It follows the right phrenic nerve.
D. *It follows the right vagus nerve.
E. It enters the right atrium.
19. Blood from epistaxis (nosebleeds) may come from a
branch of the:
A. facial A
B. maxillary A
C. opthalmic A
D. B and C but not A
E. *A, B and C
20. All of the following are characteristics of the dural
venous sinuses, EXCEPT:
A. They terminate directly or indirectly in the internal jugular vein.
B. *They lie between the dura and the arachnoid
mater.
C. Blood from diploic veins drains into them.
D. They connect with valveless veins outside the
cranial cavity.
E. They receive venous draining of the brain
21. All the following are branches of the external carotid
artery, EXCEPT:
A. ascending pharyngeal A.
B. superior thyroid A.
C. occipital A.
D. *vertebral A.
E. lingual A.
22. The carotid sheath contains all of the following,
EXCEPT:
A. internal carotid A.
B. common carotid A.
C. *sympathetic trunk
D. internal jugular V.
E. vagus N.
II. Tests from “Step-1” database (with explanation)
1. A 63-year-old man complains of trouble swallowing and hoarseness. On physical exam, he is
noted to have ptosis and a constricted pupil on
the left, and a diminished gag reflex. Neurological examination shows decreased pain and
temperature sensation on the left side of his
face and on the right side of his body. Which of
the following vessels is most likely occluded?
A. Anterior inferior cerebellar artery (AICA)
B. Anterior spinal artery
C. Middle cerebral artery (MCA)
D. Posterior cerebral artery (PCA)
E. Posterior inferior cerebellar artery (PICA)
Explanation:
The correct answer is E. The signs and symptoms in this patient are consistent with occlusion of
the posterior inferior cerebellar artery (PICA). PICA is a branch of the vertebral artery (which is itself a branch of the subclavian artery). Occlusion of
PICA causes a lateral medullary syndrome characterized by deficits in pain and temperature sensation
over the contralateral body (spinothalamic tract
dysfunction); ipsilateral dysphagia, hoarseness, and
diminished gag reflex (interruption of the vagal and
glossopharyngeal pathways); vertigo, diplopia, nystagmus, and vomiting (vestibular dysfunction); ipsilateral Horner's syndrome (disruption of descending
sympathetic fibers); and ipsilateral loss of pain and
temperature sensation of the face (lesion of the spinal tract and nucleus of the trigeminal nerve).
AICA (choice A) is a branch of the basilar artery. Occlusion of this artery produces a lateral inferior pontine syndrome, which is characterized by
ipsilateral facial paralysis due to a lesion of the facial nucleus, ipsilateral cochlear nucleus damage
leading to sensorineural deafness, vestibular involvement leading to nystagmus, and spinal trigeminal involvement leading to ipsilateral pain and
temperature loss of the face. Also, there is ipsilateral dystaxia due to damage to the middle and inferior cerebellar peduncles.
The anterior spinal artery (choice B) is a branch
of the vertebral artery. Occlusion produces the medial medullary syndrome, characterized by contralateral hemiparesis of the lower extremities and trunk
due to corticospinal tract involvement. Medial lemniscus involvement leads to diminished proprioception on the contralateral side, and ipsilateral paralysis of the tongue ensues from damage to the hypoglossal nucleus.
The MCA (choice C) is a terminal branch of the
internal carotid artery. Occlusion results in contralateral face and arm paralysis and sensory loss. Aphasia is produced if the dominant hemisphere is affected, left-sided neglect ensues if the right parietal
lobe is affected, and quadrantanopsia or homonymous hemianopsia occur when there is damage to
the optic radiations.
The PCA (choice D) arises from the terminal
bifurcation of the basilar artery. Occlusion results in
a homonymous hemianopsia of the contralateral
visual field. Often, there is macular sparing.
2. A 46-year-old man sustains a spider bite on his
upper eyelid, and an infection develops. The
physician is very concerned about spread of the
infection to the dural venous sinuses of the
brain via emissary veins. With which of the following dural venous sinuses does the superior
ophthalmic vein directly communicate?
A. Cavernous sinus
B. Occipital sinus
C. Sigmoid sinus
D. Superior petrosal sinus
E. Straight sinus
Explanation:
The correct answer is A. The anterior continuation of the cavernous sinus, the superior ophthalmic
vein, passes through the superior orbital fissure to
enter the orbit. Veins of the face communicate with
the superior ophthalmic vein. Because of the absence of valves in emissary veins, venous flow may
occur in either direction. Cutaneous infections may
be carried into the cavernous sinus and result in a
cavernous sinus infection which may lead to an infected cavernous sinus thrombosis. The cavernous
sinus is lateral to the pituitary gland and contains
portions of cranial nerves III, IV, V1, V2 and VI,
and the internal carotid artery.
The occipital sinus (choice B) is at the base of
the falx cerebelli in the posterior cranial fossa. It
drains into the confluence of sinuses.
The sigmoid sinus (choice C) is the anterior
continuation of the transverse sinus in the middle
cranial fossa. The sigmoid sinus passes through the
jugular foramen and drains into the internal jugular
vein.
The superior petrosal sinus (choice D) is at the
apex of the petrous portion of the temporal bone
and is a posterior continuation of the cavernous sinus. The superior petrosal sinus connects the cavernous sinus with the sigmoid sinus.
The straight sinus (choice E) is at the intersection of the falx cerebri and the falx cerebelli in the
posterior cranial fossa. The straight sinus connects
the inferior sagittal sinus with the confluence of
sinuses.
III. Tests of “Krok-1” database
1. A casualty has a trauma of soft tissues and parietal bones in the saggi-tal suture area with profuse bleeding. What formation is probably injured?
A. Sinus rectus.
B. Sinus petrosus superior.
C. *Sinus sagittalis superior.
D. Sinus sagittalis inferior.
E. Sinus transverses.
2. A 37-year-old victim was injured with a sharp
object in the interior region of carotid cervical
triangle. Which vessel was injured?
A. External jugular vein.
B. External carotid artery.
C. *Common carotid artery.
D. Superior thyroid artery.
E. Internal carotid artery.
3. A 30-year-old patient was hospitalized due to
bleeding of the facial artery. What place on the
face has to be pressed to stop bleeding?
A. *The mandible’s edge
B. The molar bone
C. The mental process
D. The nose’s back
E. The mandible’s branch
4. A victim of a car accident has a contused
wound in temporal region. During medical examination a fracture of zygomatic bone and
symptoms of intracranial hemorrhage are observed. Which artery might be damaged in this
region?
A. Superficial temporal.
B. *Middle meningeal.
C. Anterior meningeal.
D. Maxillary.
E. Facial.
5. An injury of skin in the medial region of the
sternocleidomastoid muscle caused air embolism. Which cervical vein was damaged?
A. Posterior auricular.
B. Anterior jugular.
C. Internal jugular.
D. *External jugular.
E. Transverse cervical.
6. After the injury of temporal region a patient got
epidural hematoma. Which artery is damaged?
A. Deep temporal.
B. *Middle meningeal.
C. Deep auriculary.
D. Superior tympanic.
E. Inferior tympanic.
7. A 56-year-old patient has worked for 28 years
at a chemical plant in a workshop with harmful
production conditions. He often has hemorrhages of the nasal cavity mucosa. Which arteries are involved?
A. *Anterior and posterior ethmoid.
B. Supraorbital.
C. Ciliary.
D. Anterior cerebral.
E. Ophthalmic.
8. A patient was admitted to a hospital with an
open fracture of the ramus of mandible and profuse bleeding in the fracture site. Which artery
is damaged?
A. A. palatina ascendens.
B. A. temporalis media.
C. A. facialis.
D. A. lingualis.
E. *A. alveolaris inferior.
9. A patient has epidural hematoma in the temporal region. Which artery is damaged?
A. *Medial meningeal.
B. Medial cerebral.
C. Posterior communicating.
D. Anterior meningeal.
E. Anterior cerebral.
10. A patient who got into a car accident has bleeding from soft tissues in front of the angle of the
mandible. Which vessel must be ligated to stop
the bleeding?
A. A. lingualis.
B. A. carotis interna.
C. A. temporalis superficialis.
D. A. alveolaris inferior.
E. *A. facialis.
11. A patient has bleeding in the region of the upper lip. Which artery is damaged?
A. A. lingualis.
B. A. maxillaris.
C. *A. facialis.
D. A. temporalis superficialis.
E. A. angularis.
12. A patient with a thymus tumor has cyanosis,
extension of subcutaneous venous network,
edema of soft tissues of the face, neck, upper
half of the body, upper limbs. Which venous
trunk is blocked?
A. *Superior vena cava.
B. External jugular vein.
C. Subclavian vein.
D. Internal jugular vein.
E. Anterior jugular vein.
13. A 50 year-old patient had hemorrhage of the
brain and was taken to the hospital. The place
of hemorrhage was revealed on the lateral hemispheres surfaces during the medical examination. What artery was injured?
A. *The middle cerebral artery
B. The posterior cerebral artery
C. The anterior cerebral artery
D. The posterior communicating artery
E. The anterior communicating artery