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Introduction to the Nervous System 4
At 1.5 cm crown-rump length, in lateral view, the brain of the cat looks as shown in
Figure 1. It would not be much different in appearance in the dog.
Fig. 1. Lateral view of neural tube of
cat, 1.5 cm crown-rump length.
From Lehrbuch der Anatomie der
Haustiere, Paul Martin, 1912:
Schickhardt & Ebner, Stuttgart.
brain
spinal cord
But the brain of a mature dog looks like this:
brain
spinal cord
Fig. 2. Canine brain, lateral view.
The main theme of this presentation is how we get from Fig. 1 to Fig. 2.
Lamina terminalis, growth of the hemispheres. With the neural tube formed and its
neuropores closed off at either end, the tube and the neural crest beside it rest in a
sea of mesoderm filled with cells and the intercellular substance that the cells have
formed. The tube is large at its anterior end, which will form the brain, and tapers by
an elongate developing spinal cord to its sealed posterior end. The anterior end of the
tube is the lamina terminalis of the adult brain. Right and left hemispheres (the
telencephalon) outpouch dorsolaterally from this anterior end, incorporating an
extension of the lumen of the tube, which will become the lateral ventricle of each.
The surrounding mesoderm differentiates to form the meninges and the fluid-filled
subarachnoid space.
Fig. 3.. Neural tube, 1 cm CR length,
median section. From Lehrbuch der
Anatomie der Haustiere, Paul Martin,
1912: Schickhardt & Ebner, Stuttgart.
Fig. 4. Neural tube, diagrammatic.
Dorsal view with hemispheres and
ventricular system further
developed.
lamina terminalis
outpouching
hemisphere
outpouching
hemisphere
lamina terminalis
Fig. 5. Median section of mature canine brain, showing
the position of the lamina terminalis. The orange arrow
passes through the interventricular foramen into the
lateral ventricle.
lamina
terminalis
Ventricular system, meninges, choroid plexus. The ventricular system of the brain
and cord results from the variable enlargement and extension of the lumen of the
neural tube. Diagrammatically:
olfactory bulb
of hemisphere
Fig. 6. The drawing is from
Lehrbuch der Anatomie der
Haustiere, Paul Martin, 1912:
hemisphere
(telencephalon)
diencephalon
(thalamic
portions)
mesencephalon
(midbrain)
metencephalon
(pons, cerebellum)
rhombencephalon
myelencephalon
(medulla oblongata)
medulla spinalis
(spinal cord)
1
3
2
CAq
4
CeCa
Ventricles 1 and 2 are the lateral ventricles, one in each hemisphere; the lateral
ventricle is curved, like the hemisphere. A slender extension from the anterior end of
the lateral ventricle passes anteriorly in the olfactory stalk to a small chamber within
the olfactory bulb. Each lateral ventricle communicates with the 3rd ventricle by way of
the interventricular foramen. The third ventricle is central between the thalamic nuclei
of each side. It completely separates R and L thalamic nuclei until their growth results
in a median interthalamic adhesion. The adhesion is central and converts the
undivided chamber into a circular one. No crossing of fibers or intermixing of right and
left side cells occurs at the adhesion. From the 3rd ventricle, the cerebral
(mesencephalic) aqueduct, a narrow passage, extends posteriorly to the 4th ventricle.
The 4th ventricle is a large chamber within the rhombencephalon (metencephalon +
myelencephalon). At its posterior end, the obex of the 4th ventricle, the chamber is
continuous with the central canal of the spinal cord.
Figs. 7, A, B. show the growth of the thalamic nuclei to form the interthalamic
adhesion, converting the undivided 3rd ventricle to a circular chamber:
Figs. 7, A, B. Both figures (the B figure has been modified slightly) are from Lehrbuch
der Anatomie der Haustiere, Paul Martin, 1912: Schickhardt & Ebner, Stuttgart. A is a
median section through the developing brain of a 1.6 cm CR length cat embryo; B is a
growing
thalamic
nuclei X
infundibular
recess
A
interventricular foramen
lamina terminalis
optic recess
Interthalamic adhesion
rd
3 ventricle
B
Above (dorsal to) the pons, the roof of the fourth ventricle becomes thicker and
folded, growimg to form the cerebellum. Anterior and posterior to the developing
cerebellum, the roof remains as a thin covering: the anterior and posterior medullary
vela.
Fig. 8. Neural tube, 1 cm CR length,
median section. From Lehrbuch der
Anatomie der Haustiere, Paul Martin,
1912: Schickhardt & Ebner, Stuttgart.
4th ventricle
roof of 4th ventricle
prior to growth of the
cerebellum
Fig. 9. Cat, 1.6 cm CR length, median section
showing beginning development of the cerebellum
and the medullary vela. From Lehrbuch der Anatomie
der Haustiere, Paul Martin, 1912: Schickhardt &
Ebner, Stuttgart.
anterior
medullary velum
cerebellum
X
4th ventricle
Fig. 10. Dorsal view
of canine brain with
much of the dorsal
part of the
hemispheres cut
away. The roof of the
third ventricle is
removed. The
cerebellum and most
of the vela are
removed; the 4th
ventricle is exposed.
posterior
medullary velum
posterior colliculus
anterior medullary velum (cut)
4th ventr.
posterior medullary velum (cut)
Fig. 11. Median section through the canine brain. The anterior half of the
cerebellum and the anterior medullary velum are indicated.
mesencephalic aqueduct
anterior medullary velum
4th ventricle
Meninges and choroid plexus. The meninges arise by differentiation of the
mesenchyme surrounding the neural tube. They are connective tissue membranes
that condense around the brain and spinal cord with sleeve-like extensions that
envelop the roots of the spinal nerves and the spinal ganglia. At the spinal ganglion,
the membranes fuse together and are continuous with the connective tissue of the
ganglion and the epineurium of the spinal nerve. From within outward there are three
meninges, the pia mater, arachnoid mater, and dura mater. In the guinea pig, the
arachnoid mater has been shown to be an artifactually created membrane brought
about by separation (fracturing) of the light-cell layer of the dura (see The Subdural
Space Interpreted as a Cellular Layer of Meninges, Richard D. Frederickson, Anat.
Rec., 230, 38-51 1991). We treat the two membranes as an inseparable duraarachnoid. Between the dura-arachnoid mater and the pia mater is the subarachnoid
space, which is lined by a mesothelium and filled with cerebrospinal fluid (CSF). The
CSF functions, in part, in providing a fluid cushion for the brain and cord. The
subarachnoid space communicates with the ventricular space at the lateral aperture
of each of the lateral recesses of the fourth ventricle. The opening is just dorsal to the
acoustic tubercle and ventral to the choroid plexus of the fourth ventricle. In humans,
there is often a median, third, aperture at the posterior end of the fourth ventricle.
Fig. 12. Canine
brain. Dorsal view of
4th ventricle,
showing its lateral
recesses.
acoustic tubercle
vestibulocochlear
(VIIIth cranial) nerve
nerve
4th ventr.
lateral recess
Fig. 13. Lateral view of canine brain,
left hemisphere removed. Arrow
points to the position of the lateral
aperture between the acoustic
tubercle and the choroid plexus.
choroid
plexus
The pia mater is a loose, chiefly collagenous, connective tissue intimately applied to
the surface of the brain and spinal cord with a thin layer passing with the vessels that
penetrate the nervous tissue. The larger vessels upon the surface of the brain and
cord also pass within a thin layer of the pia mater. A mesothelium is applied to its
surface that faces the subarachnoid space. Numerous isolated slender bundles of
fibers, arachnoid trabeculae, clothed with a mesothelium, pass between the deep
surface of the dura-arachnoid and the deeper lying pia.
Fig. 14. The meninges at brain level. From
http://vanat.cvm.umn.edu/neurHistAtls/pages/images/Men1.jpg .
subarachnoid space
Choroid plexuses, structure and topography. The choroid plexus elaborates the
cerebrospinal fluid. Each choroid plexus is composed of 1. A network of vessels that
develops in relation to specific parts of the walls of the lateral, third, and fourth
ventricles, 2. The tela choroidea, the web-like connective tissue supporting the
capillaries of the vascular network, and 3. A simple layer of cuboidal ependymal cells
that faces the lumen of the ventricle and secretes the cerebrospinal fluid. In the area
where the plexus develops, the neural tube thins to a single ependymal cell layer. The
ependymal cells are joined by occluding junctions, which assure that the composition
of the CSF is regulated by the ependymal cells.
(ependyma)
Fig. 15. Choroid plexus from the developing brain, lateral ventricle, of the cat; A,
low power, B, about100x. From: Ronald A. Bergman, Ph.D., Adel K. Afifi, M.D.,
Paul M. Heidger, Jr., Ph.D.
www.anatomyatlases.org/MicroscopicAnatomy/Section06/Plate06132.shtml
Choroid plexuses of the lateral and third ventricles. Choroid plexuses are present
in each lateral ventricle, in the roof of the third ventricle, and, as a pair, in the roof of
the fourth ventricle. Each plexus of the lateral ventricle develops as a delicate
infolding of its medial wall along the line of the hemisphere’s joining the diencephalon
(this is at the stria terminalis, which marks the junction). At the level of the
interventricular foramen each choroid plexus of the lateral ventricle joins the choroid
plexus of the third ventricle. This is shown in the two figures that follow; Martin’s
diagrams are only slightly modified from the original.
Fig. 16. Cross-section through the brain at the level of the developing
interthalamic adhesion. Diagrammatic. From Lehrbuch der Anatomie der
Haustiere, Paul Martin, 1912: Schickhardt & Ebner, Stuttgart.
choroid plexus of
the third ventricle
hemisphere
choroid plexus of the lateral
ventricle, formed from a
thinning and infolding of the
ventricular wall
thalamus
Fig. 17. Cross-section
through the brain,
lateral
showing the continuity
ventricle
of choroid plexuses of
lateral and third
ventricles at the level
of the interventricular
foramen.
Diagrammatic. From
Lehrbuch der
Anatomie der
Haustiere, Paul
interventricular
Martin, 1912:
foramen
Schickhardt & Ebner,
The following figures show the topography of the choroid plexuses of lateral and third
Stuttgart.
third
ventricle
ventricles in the mature equine brain. The arrangement is similar
in the
human brain
and all of the mammals that we study. The fold of choroid plexus of each lateral
ventricle, which is a part of the wall of the ventricle, extends from the stria terminalis
at the junction of the hemisphere with the thalamus to the lateral edge of the fimbria
of the hippocampus and the fornix of the hemisphere.The figures are taken from
Guide for the Laboratory Examination of the Anatomy of the Horse, A. Horowitz,
1965; University Bookstore, The Ohio State University.
Fig. 18A. Brain, dorsal aspect with roof of the lateral ventricles (corpus callosum)
removed. The position of the subcortical nuclei of the right hemisphere is indicated.
The representation of the nuclei is taken from Neuroanatomy, A Programmed Text
by Sidman and Sidman, Little, Brown and Company.
Fig. 18B. Brain, dorsal aspect. Structures forming the floor of the lateral ventricle
are cut posteriorly and reflected forward to reveal the underlying thalamus,
midbrain, anterior cerebellum, and choroid plexuses of 3rd and lateral ventricles..
choroid plexus of
the lateral ventricle
(yellow)
Interventricular
foramen
fornix
A
B
Choroid plexuses of 4th ventricle, arachnoid granulations, cerebrospinal fluid
flow.
The choroid plexuses of the 4th ventricle are paired, right and left. A part of the plexus
is prolapsed from the lateral aperture and rests in the subarachnoid space ventral to
the posterior cerebellum. See Figs. 19 and 20.
Fig. 19. Canine brain
with the cerebellum
removed to show the
choroid plexuses of the
4th ventricle.
R, L choroid plexuses,
prolapsed part
VIIIth cranial nerve
posterior
medullary velum
R and L choroid
plexuses (from the
deep side of the
medullary velum)
Fig. 20. Cross-section
through the 4th
ventricle at the level
of the lateral aperture.
Diagrammatic.
choroid plexus,
prolapsed part
lateral aperture
acoustic tubercle
R and L choroid
plexuses (from the
deep side of the
4th ventriclefluid is elaborated by the choroid plexuses and is thought to be
Cerebrospinal
medullary velum)
absorbed 1. (presumably) by the arachnoid granulations of the arachnoid membrane,
2. by lymphatic vessels of the spinal and cranial nerves, and 3. by way of the olfactory
nerves and the lymphatic vessels of the nasal cavity. The arachnoid granulations are
evaginations of the arachnoidea (arachnoid mater) that perforate the dura and the
wall of a venous sinus to end blindly in the lumen of the sinus where they are thought
(this is not universally accepted) to secrete cerebrospinal fluid into the bloodstream.
Fig. 21. Diagram of the arachnoid granulations. From:
http://instruct.uwo.ca/anatomy/530/530notes.htm
A brief explanation of terms: Venous sinuses are veins that lack valves and are
without smooth muscle in their walls. Dural venous sinuses are veins found between
the folds of the cranial dura mater or between the cranial dura and the periosteum of
the cranial vault (some authors describe this periosteum as the “dural periosteum” or
the “periosteal layer of the dura”). The veins that proceed from the brain capillaries
pass upon the brain’s surface in relation to the pia mater, which provides a thin
covering (see Fig. 14). They are designated cerebral and cerebellar veins and pass in
the subarachnoid space to perforate the dura and discharge into a dural venous
sinus. The dural venous sinuses are drained by emissary veins that pass through the
different skull foramina to discharge in the extracranial veins, chiefly tributaries of the
internal and external jugular veins.
Normal flow of the CSF. In the normal case, CSF produced by the choroid plexuses
flows freely from its origin, passes out the lateral apertures into the subararachnoid
space, and is absorbed at the arachnoid granulations and by way of the lymphatic
vessels of the spinal and cranial nerves and of the nasal mucosa. The CSF normally
maintains a maximum pressure of about 86.5 mm water (dog) to 379 mm (horse). An
increased pressure with accumulation of fluid results when there is a blockage in the
path of flow (non-communicating hydrocephalus) or a failure of adequate absorption
(communicating hydrocephalus). The mesencephalic aqueduct is the most common
site of blockage.
Fig. 22. Ventricular
system, dog.
Corpus callosum, hippocampus, and fornix. The corpus callosum, the largest of
the commissures joining the right and left halves of the brain, first appears as a
rounded bundle of fibers at the dorsal part of the lamina terminalis. With addition of
fibers by interposition and apposition, it grows posteriorly and its form is altered
according to the growth of the hemisphere. It develops a curvature, the splenium, that
follows the growth and form of the posterior hemisphere. In the dog, growth of the
hemisphere and addition of fibers rostrally results in the separation of the corpus
callosum from the lamina terminalis. In all mammals, there is a development of an
anterior curvature, the genu. In some species, equine and bovine, for example, and in
humans, a more slender band of fibers extends ventrocaudally from the genu,
retaining the connection of the genu to the lamina terminalis. This part is designated
the rostrum of the corpus callosum. The writer has not observed rostrum fibers in the
dog. The body (truncus) of the corpus callosum is elongate, between the genu and
splenium, and is its largest part. The part of the medial hemisphere enclosed by the
curvature of the corpus callosum becomes the septum pellucidum. According to
Martin (1912), sometimes the two hemispheres fuse in this area, sometimes not. With
absence of fusion, a space remains, the cavum septi.
Fig. 23. Martin’s original figure of a median section (at the level of
the lamina terminalis) of a 4 cm crown rump length cat embryo.
From Lehrbuch der Anatomie der Haustiere, Paul Martin, 1912:
Schickhardt & Ebner, Stuttgart.
fiber-bundle of beginning
corpus callosum
olfactory bulb
lamina terminalis,
somewhat thickened at
this stage
hippocampal
sulcus
Fig. 24 A, B. A modification of Martin’s original
figure illustrating the manner of growth of the
corpus callosum with the expanding
hemispheres and fibers extending between R
and L hemispheres as described by Martin.
corpus callosum
A
corpus callosum
septum pellucidum
developing thalamus
B
Hippocampus, fornix. The choroid fissure is the external sulcus that results from the
infolding of the thin ventricular wall that becomes the choroid plexus. The
hippocampal sulcus results from the infolding of the normal-thickness cerebral cortex
in the posteroventromedial hemisphere, the part that will develop into a portion of the
temporal lobe.
Fig. 25. Martin’s figure.
Cross-section of
hemisphere at the level of
the thalamus. From
Lehrbuch der Anatomie der
Haustiere, Paul Martin,
1912: Schickhardt & Ebner,
Stuttgart.
hippocampal sulcus
choroid fissure
Fig. 36. Martin’s figure,
modified. From Lehrbuch
der Anatomie der
Haustiere, Paul Martin,
1912: Schickhardt & Ebner,
Stuttgart.
choroid plexus
of 3rd ventricle
choroid fissure
hippocampal sulcus
Fig. 37. Martin’s figure, modified to show the developing corpus
callosum and interthalamic adhesion. From Lehrbuch der Anatomie
der Haustiere, Paul Martin, 1912: Schickhardt & Ebner, Stuttgart.
corpus callosum
choroid plexus,
3rd Ventricle
interventricular
foramen
lamina terminalis
3rd ventricle
Interthalamic
adhesion
(developing)
The hippocampus is formed in the posteroventromedial part of the hemisphere, the
part that overlies the thalamus and midbrain. The union of the hemispheres with the
diencephalon (diencephalon = epithalamus, metathalamus, thalamus, subthalamus,
and hypothalamus) is wedge-shaped.
Fig. 28. Dorsal view of an early
stage of hemisphere
development from the anterior
neural tube. The oblique lines
(marked by black arrows) mark
the junction of the hemispheres
(telencephalon) with the
diencephalon. Interventricular
foramen, yellow double-arrow.
But a dorsal view of the developed brain looks like this:
Fig. 29. Dorsal view of
the canine brain.
If the dorsal part of the hemispheres is cut away to expose their union with the
diencephalon, it looks like this in dorsal view:
Fig. 30. Union of the
hemisphere with the
diencephalon (indicated
by black arrows), dog.
Interventricular foramen,
yellow double-arrow.
All of the diencephalon and that part of the midbrain (mesencephalon) that is not
covered by the anterior cerebellum lie chiefly ventral to the posteroventromedial part
of the hemisphere. This is shown in the following views:
Fig. 31. Medial view of
canine brain with left
hemisphere removed at
its union with the
diencephalon.
I
Fig. 32. Lateral view of
canine brain with parts
hidden by the hemisphere
indicated.
The infolded choroid plexus and hippocampal cortex look like this in cross-section
(semi-diagrammatic, at the level of the tail of the caudate nucleus):
corpus callosum
lateral ventricle
hippocampus
caudate nucleus, tail
stria terminalis
choroid fissure
hippocampal sulcus
THALAMUS
midline
Fig. 33. Rostral view of cross-section of right
hemisphere at the level of the lateral ventricle.
The drawing of the hippocampus (dog) is taken
from Lehrbuch der Histologie und
Vergleichenden Mikroskopischen Anatomie der
Haustiere, Krölling, O. and Grau, H.: 1960,
Verlag Paul Parey.
The pyramidal cells of the hippocampus give rise to axons that, myelinated, pass
upon the ventricular surface where they form a thin white coat, the alveus. The alveus
is separated from the cavity of the ventricle only by the ependyma (layer of
ependymal cells). These fibers incline laterally to the margin of the choroid fissure
where they gather as a large bundle, the fimbria. The fimbriae of the two hemispheres
pass dorsally and rostromedially. Reaching the midline, the fiber-bundles are in
apposition, ventral to the fibers of the corpus callosum where they are joined to each
other and to the callosal fibers only by glia (neuroglial cells). The bundles join at the
midline only briefly, their apposition forming the body of the fornix. Continuing forward,
the fiber-bundles again begin to separate at the level of the lamina terminalis, dorsal
to the rostral (anterior) commissure. The separating bundles, as the columns of the
fornix, pass ventrally caudal to, and rostral to, the anterior commissure. The largest
part, which is the part that passes caudal to the anterior commissure, continues
caudally in the grey matter of the wall of either side of the third ventricle. These right
and left columns of the fornix dispatch fibers to nuclei of the hypothalamus and its
mammillary bodies.
Fig. 34. The origin
of the fiber-bundle
designated the
fimbria.
alveus
pyramidal cells
fimbria
stria
Note that the choroid plexus, part of the original wall of the neural tube, extends
from the lateral margin of the fimbria to the stria terminalis.
body of fornix
crus of fornix
Terminology of the fornix:
hippocampal
commissure
Fig. 35.
Fimbriae
and fornix.
column of fornix
fimbria
mammillary body
Note: This drawing appears to be one of Frank Netter’s. I took it from an internet site
of fornix images. No indication of the artist was given.
Fig. 36. Canine brain, dorsal view with corpus callosum
removed, revealing the floor of the lateral ventricles. The
larger figure has the hippocampal part of the hemisphere and
much of the fornix removed on the left side. The roof of the
third and fourth ventricles, and the cerebellum, are removed.
The thalamus and brainstem are exposed.
R, L hippocampus
hippocampus
R, L choroid
plexus
R, L caudate
nucleus
hippocampus
fimbria
choroid plexus of
lateral ventricle
body of fornix, left part cut away
crus of fornix
Interventricular
foramen (yellow)
caudate nucleus
grey matter of septum
pellucidum (septal
nuclei)
Fig. 37. Median section, canine brain. The dots indicate
the course of the R column of the fornix in its caudal
path deep to the wall of the 3rd ventricle.
septum pellucidum and
septal grey (nuclei)
hippocampal
commissural fibers
corpus callosum
R, L
fimbria
column of
fornix
body of fornix
anterior
commissure
mammillary body
Fig. 38. Cross-section through the brain of a sheep at the level of
the third ventricle. The columns of the fornix can be seen deep to
the wall of the third ventricle. Hematoxylin stain.
Fig. 39. Brain (canine), lateral view with the position of the hippocampus
superimposed. This figure also gives the approximate position of the caudate
nucleus, amygdaloid body (amygdala), and corpus striatum (lentiform
nucleus and globus pallidus). The stria terminalis, which is a narrow bundle
of fibers arising chiefly from the amygdala and arching dorsally and rostrally
alongside, and medial to, the tail and body of the caudate nucleus, is not
shown here. Like the lamina terminalis, its position indicates a boundary, in
this case between the thalamus and the hemisphere.
caudate nucleus
body
tail
hippocampus
fimbria
corpus striatum
amygdala
caudate nucleus
tail, body, head
interventricular
foramen (yellow)
stria terminalis
3rd ventricle
thalamus
lateral geniculate
body
telae choroideae
(attachments), choroid
plexus of 3rdventricle
pineal body
medial geniculate
body
thalamus
Fig. 40. Dorsal view of the left caudate
nucleus, stria terminalis and thalamus of
the dog.
This presentation has mainly considered how important features of the forebrain,
telencephalon and diencephalon, are derived from the primitive neural tube. The
cerebrum is generally defined as the cerebral hemispheres and the diencephalon
(thalamus, and epi-, meta-, sub-, and hypo-thalamus). The mesencephalon is
sometimes included. The cerebral cortex is the seat of consciousness and functions
of memory, learning, behavior, and attention all take place there. The cerebral cortex
is also the site of initiation of voluntary, deliberate, motor activity. We think of
sensations being appreciated and associated/integrated in the cerebral cortex to
provide the animal’s response. By way of a limited and somewhat simplified (but
valid) example, the horse hears, sees, and smells its owner bringing hay and, owing
to what the horse has learned from previous experience and the animal’s memory of
it, responds to this input often by a deliberative movement of its body and a
characteristic sound (“whinny”). Some visceral sensations are also being received
and may modify the animal’s behavior. All involving important cortical functions.
Hippocampal connections and function in humans. The hippocampus is an
infolded part of the cerebral cortex. Myelinated axons from the hippocampal pyramidal
neurons pass by way of the fimbria and fornix to the septal nuclei, to the
hypothalamus, and to the mammillary bodies. Some fibers also pass in a reverse
direction. In humans, and some of these ideas have originated in animal
experimentation, the hippocampus is thought to have a prominent effect on memory
and is presently subject to a considerable research owing chiefly to the interest in
Alzheimer’s disease. In our domestic animals this part of the brain has also been
studied owing to its cytological examination in the diagnosis of rabies in which there
are present Negri bodies, eospinophilic inclusions in the cytoplasm of hippocampal
neurons.
Stria terminalis connections and function in humans. The amygdaloid body is a
very large collection of neurons, a nucleus, that is responsible for the prominence of
the rostroventral part of the piriform lobe; it is close to, and has connection with, the
ventral extremity of the hippocampus. The stria terminalis is a collection of fibers
(myelinated axons) arising from amydaloid neurons. The stria passes to the area of
the interventricular foramen from which its branches pass chiefly to the septal nuclei,
the thalamus, and hypothalamus. There are also fibers passing from these areas to
the amygdaloid body. In humans, the stria is thought to mediate certain behavioral
and emotional effects.
Hippocampal and strial function in animals. Other than for those observations in
animal experiments, and the effect of hippocampal disease in rabies, the writer knows
of no specific function for these structures in animals. These structures are a part of
the areas of the hemisphere associated with the olfactory sense. All of the mammals
that we study are macrosmatic, having an elaborate sense of smell. The animal uses
this sense to obtain food, to protect itself, to find a mate for reproduction. It is probably
the most important sense for these animals and has undoubtedly wide effect on their
behavior. The hypothalamus is a part of the brain from which prominent autonomic
pathways proceed. These are pathways involved in regulating heart rate, blood
pressure, body temperature, thirst, and the desire for food or abstinence from eating.
In this respect, the association of the sense of smell with the hypothalamus makes
sense even if it does not now allow us an entirely satisfying, complete. explanation.