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Thirteen
The Human Nervous slstem: An Anetomical WewoinL
Sixth Edition, M\ftay L. Bffi and John A, Kiemil. J.B.
Lippincort Company, Philadelphia, @ 1993.
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The large surface area of the human cerebral cortex results in a pattern of
gyri and sulci. Some of these convolutions are important anatomical landmarks or functional areas.
Five lobes (including the insula) are recognized in each cerebral hemisphere.
On the medial surface of the hemisphere, the parieto-occipital sulcus
separates the parietal from the occipital lobe.
In the occipital lobe, the calcarine sulcus is the site of the primary visual
conex.
In the parietal lobe, the postcentral gyrus corresponds to the first general
sensory area. The supramarginal and angular gyri are parts of the receptive
language area, which e>rtends onto the superior temporal gyrus.
The central sulcus is between the parietal and frontal lobes, separating the
first somesthetic from the primary motor area.
ln the frontal lobe, the precentral gyrus corresponds to the primary motor
area. The olfactory bulb and tract are applied to the orbital surface of the
frontal lobe.
The lateral sulcus (syMan fissure) separates the frontal and parietal lobes
from the temporal lobe.
The insular lobe (insula), in the floor of the lateral sulcus, is a landmark for
part of the corpus striatum.
The superior surface of the superior temporal gyrus includes the primary
auditory area.
The parahippocampal gyrus includes the uncus (a primary olfactory area)
and the entorhinal area, which has olfactory and limbic functions.
The "limbic lobe" includes the parahippocampal and cingulate gyri. It is
part of the limbic system, which is involved in memory.
222
,oinl,
J.B.
Chapter 13: Topography of the Cerebral Hemispheres
tional importance, whereas others have no
known significance. They are described and
illustrated in the later sections of this chapter.
The complicated folding of the surface of the
cerebral hemispheres substantially increases
the surface area and, therefore, the volume of
cerebral cortex. The folds or convolutions are
called gyti, and the intervening grooves are
called sulci, About two-thirds of the cortex
forms the wplls of the sulci and is, therefore,
hiddenfrom surface view. Although some gyri
are constant features of the cerebral surface,
Major Sulci
The lateral and parieto-occipital sulci appear
early in fetal development and are especially
deep in the mature brain. These, together with
the central and calcarine sulci, are the boundaries for division of the cerebral hemisphere
into the frontal, parietal, temporal, and occipital lobes (Figs. 13-f and 13-2).
The lateral sulcus (fissure of Sylvius or
sylvian fissure) begins as a deep furrow on the
inferior surface of the hemisphere. This is the
stem of the sulcus, which extends Iaterally
between the frontal and temporal lobes and
divides into three rami on reaching the lateral
surface. The posterior ramus is the main part
of the sulcus on the lateral surface of the hemi-
others vary from one brain to another and
even between the two hemispheres of the
same brain. Subtler depressions in the cerebral
cortex are grooves and notches unrelated to
the pattern of gyri and sulci. They are made by
extracerebral structures such as the bones of
the skull and the venous sinuses of the dura
mater.
A sulcus is a groove on the surface of a
cergbral hemisphere, whereas a fissure is a
cleft that separates large components of the
brain. Despite the different definitions of sulci
and fissures, the two terms often are used interchangeably for the deepest sulci.
At an early stage in studying human neuro-
sphere, whereas the anterior and ascending
rami project for only a short distance into the
frontal lobe. Al area of cortex called the insular lobe or insula (island of ReiI) lies at the
anatlmy, the student should
be able to delineate
the llbes of the cerebral hemispheres and to recognize the major sulci, fissures, and gyri, which com'
bottom of the lateral sulcus and is hidden from
monly are referced to as landmarks. Of the
smaller sulci and gyri, some are of great func-
sur{ace view. This cortex appears to have been
bound to the underlying corpus striatum dur-
Central
su
lcus
/-{,
Figure l3-1. Lobes of the cerebral hemisphere (lateral surface).
223
224
Regional Anatomy of the Central Neruous System
Central
su I cus
Parieto-occipital
sulcus
Solenium
\
nortrur I
I "":,\
Iobe
of corpus
Figs
callosu m
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in
fr
later
surfi
paft
post
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I
are
(
sign
their
Stem of lateral sulcus
Calcarine
sulcus
Preoccioital
notch
rior end of the corpus callosum and follows an
arched course to the occipital pole. In some
brains, the sulcus continues over the pole for a
short distance on the lateral surface. The calcarine sulcus is an important landmark for the
visual cortex, most of which lies in the walls of
the sulcus.
The parieto-occipital sulcus extends
from the calcarine sulcus to the superior border of the hemisphere, which it intersects
about 4 cm from the occipital pole,
The longitudinal and transverse cerebral
fissures are external to the hemispheres and
the I
fron
1
lobr
later
men1 growth of the sunounding cortex would
then produce the deep lateral sulcus.
The central sulcus (sulcus of Rolando;
rolandic sulcus) is an important Iandmark for
the sensorimotor cortex because the general
sensory area is immediately behind the sulcus
and.the motor area is immediately in front of
it,,The central sulcus indents the superior border of the hemisphere about I cm behind the
face of the hemisphere begins under the poste-
hemisphere (medial and inferior surfaces).
ing late embryonic and early fetal develop-
midpoint between the frontal and occipital
poles. The sulcus slopes downward and. forward at an angle of 70o to the vertical, stopping just short of the lateral sulcus, and there
usually are two bends along its course. The
central sulcus is about 2 cm deep, and its
walls, therefore, constitute much of the sensorimotor cortex,
The calcarine sulcus on the medial sur-
Figure l3-2. Lobes of the cerebral
.
are, therefore, in a different category from the
two
foregoing surface markings. The
longitudinal cerebral fissure separates the hemi-
the
spheres, and a dural partition called the falx
cerebri extends into the lissure. The corous
callosum, which constitutes the main cerebral
commissure, crosses from one hemisphere to
the other at the bottom of the longitudinal
midr
fissure, The transverse cerebral fissure intervenes between the cerebral hemispheres
above and the cerebellum, midbrain, and di-
encephalon below. The posterior part of this
fissure is between the cerebral hemispheres
and the'cerebellum; it contains a dural partition known as the tentorium cerebelli. The
anterior part of the transverse fissure intervenes between the corpus callosum and the
diencephalon. It is triangular in outline, tapering anteriorly, and contains the tela choroidea,
which consists of vascular connective tissue
derived from the pia mater that covers the
brain. The tela choroidea is continuous with
the connective tissue core of the choroid plexuses of the lateral ventricles and the third ventricle, and the plexuses are completed by choroid epithelium derived from the ependymal
lining of the ventricles.
tr
tal n
sulcr
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and
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Cerebral
bers
the n
Each cerebral hemisphere has lateral, medial,
and inferior surfaces on which the extent of the
sum
Hemispheres
,
stitut
the
t
Chapter 13: Topography of the Cerebral Hemispheres
lobes of the hemisphere are now defined (see
Figs.
l3-r and 13-2).
frontal lobe occupies the entire area
in front of the central sulcus and above the
The
lateral sulcus onthe lateral surface. The medial
surface of the frontal lobe envelops the anterior
part of the corpus callosum and is bounded
posteriorly by a line drawn between the central sulcus and the corpus callosum. (Such lines
are drawn elsewhere; they have no functional
significance and can be ignored after serving
their initial purpose.) The inferior surface of
the frontal lobe rests on the orbital plate of the
tl
frontal bone.
e
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o
il
I-
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The natural boundaries of the parietal
lobe on the lateral surface are the central and
lateral sulci. The other boundaries consist of
two lines; the first of these is drawn between
the parieto-occipital sulcus and the preoccipital hotch, and the second line runs from the
middle of the one just established to the lateral
sulcus. (The preoccipital notch is an inconspicuous landmark consisting of a shallow indentation of the brain formed by the petrous
portion of the temporal bone.) On the medial
surface, the parietal lobe is bounded by the
frontal lobe , corpus callosum, calcarine sulcus,
and parieto-occiPital sulcus'
The temporal lobe is outlined on the lateral surface by the lateral sulcus and the lines
previously noted. The inferior surface of the
temporal lobe extends to the temporal pole
from a line drawn between the anterior end of
the calcarine sulcus and the
preoccipital
notch. Most of the occipital lobe appears on
the medial surface of the hemisphere, where it
is separated from the temporal lobe, as alre ady
)-
al
described, and from the parietal lobe by the
parieto-occipital sulcus. On the lateral surface,
the occipital lobe consists of the small area
posterior to the Iine that joins the parietooccipital sulcus and preoccipital notch,
The portion of the great cerebral commissure in and near the midline is known as the
trunk of the corpus callosum, and the fibers of the commissure that spread out within
the medullary centers of the hemispheres con-
il,
le
stitute the radiations of the corpus callosum. Names are assigned to certain regions of
the trunk of the commissure (see Fig. I)-21;
these regions are used as reference points further on. The enlarged posterior portion of the
trunk is called the spleniurn. The anterior
portion, or genu, curves ventrally and thins
out to form the rostrurn. This is continuous
with the Iamina terrninalis, which limits the
third ventricle anteriorly,
Gyri and Sulci
Some surface markings of the hemisphere are
Iandmarks for important l'unctional areas; the
central sulcus for the sensorimotor cortex and
the calcarine sulcus for the visual cortex are
examples. For the most part, the sulci and gyri
serve only as a rough frame of reference for
cortical areas whose functions may or may not
be known. The markings can be identified according to lobes for the Iateral surface, but this
is not practicable for the medial and inferior
surfaces.
The text and illustratilns that
fllllw
apply to
sulci and gyri of varying functional significance.
The student may need to refer to this material when
studying the localization of functions in the cerebral
corta
(see
Ch.
15),
Iateral Surface
Frontal Lobe
The precentral sulcus (often broken into two or
more parts) runs parallel to the central sulcus;
these sulci outline the precentral ryrus, which is
a landmark for the primary motor area of the
cerebral cortex (Fig. 13-3). The remainder of
the lateral surface of the frontal lobe is divided
into superior, middle, and inferior frontal glriby
the superior and inferior frontal sulci. The anterior and ascending rami of the lateral sulcus
dMde the inferior fiontal gyrus into opercular,
triangular, and orbital portions, In the left hemisphere, the opercular and triangular portions
consist of cortex of l3roca's expressive or motor
speech area. In the frontal lobe, as in the other
lobes of the hemisphere, there are secondary
gyri and sulci that contribute to the variable
topography of different brains.
Parietal Lobe
The postcentral sulcus runs parallel to the cen-
tral sulcus; these sulci bound the postcentral
225
226
Regional Anatomy of the Central Ne/vous Systefi
Precentral sulcus
Postcentral sulcus
I
Superior
ntraparietal
su tcus
frontal
Central sulcus
su Icus
I
nf
erior temporal sulcus
Superior temporal sulcus
Figure l3-3. Gyri and sulci on the lateral surface of the right cerebral hemisphere. (A), (B) and (C) indicate the opercular, triangular, and orbital portions of
the inferior frontal gyrus, respectively. ( x 0.63)
ryrus, which is the landmark for the first general
sensory (somesthetic) area of corto( The intraPafietal sulcus extends posteriorly from the
postcentral sulcus and dMdes that part of the
surface not occupied by the postcentral gyrus
into superior and inferior parietal lobules. Those
portions of the inferior parietal lobule that surround the upturned ends of the lateral sulcus
and superior temporal sulcus are called the supramarginal grrus and the angular ryrus, respectively. In the left hemisphere, these gyri
consist of corte>< included in the receptive language area, which is necessary for perception and
interpretation of spoken and written language.
Temporal Lobe
Superior and inferior temporal sulci dMde the
lateral surface of the temporal lobe into superior, middle, and inferior temporal ryri. Among
variations in the temporal lobe, the inferior temporal sulcus may be discontinuous, making it
difficult to identify. The superior temporal gyrus
has a large surface that forms the floor of the
lateral sulcus. On this surface, transverse tem-
poral
ryri (also known as Heschl's
convolu-
tions) extend to the bottom of the lateral sulcus
and mark the location of the auditory area of
cortex. The posterior part of the left superior
temporal gyrus forms part of the receptive lan-
Chapter
guage area, which oxtends onto the parietal
lobe.
Occipital Lobe
In the brains of primates other than humans
and in some human brains, the calcarine sulcus
continues for a short distance over the occipital
a curved lunate sulcus
around the end of the calcarine sulcus. Except
pole. There is then
for this inconstant marking, the small area of the
occipital lobe on the lateral surface has minor
grooves and folds of no special significance.
lnsular Lobe (lnsula)
The regions that conceal the insula are known
as the frontal, parietal, and temporal opercula;
they must be spread apart or cut awayto e)pose
the insula (Fig. 13-4), The insula is outlined by a
circular sulcus and is divided into two regions
by a central sulcus. Several short gyri lie in front
,
of the central sulcus, and one or two long gyri lie
behind it. The inferior part of the insula in the
region of the stem of the lateral sulcus is known
as the limen insulae.
The insula is an important landmark for certain structures inside the cerebral hemisphere.
The lentiform nucleus, a component of the corpus striatum, is separated from the insula bytwo
layers of white matter (the extreme and e>cternal
capsules) and an intervening layer of gray mat-
ter (the claustrum).
i3:
Topography oJ the Cerebral Hemispheres
Medial and lnferior Surfaces
The cingulate ryrus begins beneath the genu of
the corpus callosum and continues above the
corpus callosum as far back as the splenium
(Fig. 13-5). The gyrus is separated from the
corpus callosum by the sulcus of the corpus
callosum (callosal sulcus).'The superior surface
of the corpus callosurn is covered by a very thin
layer of cortical gray rnatter known as the indusium griseum. The cingulate sulcus intervenes
between the cingulate gyrus and the medial
frontal grrus, which is continuous with the superior frontal gyrus on the lateral surface of the
hemisphere. The cingulate sulcus gives off a
paracentral sulcus and then divides into marginal and subparietal sulci in the parietal lobe.
The region bounded by the paracentral and
marginal sulci, which surrounds the indentation
made by the central sulcus on the superior border, is called the paracentral lobule. The anterior
and posterior parts of the paracentral lobule are,
respectively, extensions of the precentral and
postcentral gyri of the lateral surface of the
hemisphere, The area above the subparietal
sulcus is called the precuneus and is continuous with the superior parietal lobule on the
lateral surface. The parieto-occipital and calcarine sulci bound the cuneus of the occipital
lobe.
On the medial suuface of the frontal lobe,
underneath the rostrum of the corDus calCircular sulcus
f
Figure ll-4. The insula (island
of
Reil) of the left cerebral hemisphere,
by cutting away the frontal,
parietal, and temporal opercula.
e<posed
(
x
1.8)
\\!
Long gyri
,.
227
Central sulcus
Paracentral sulcus
Marginal sulcus
Cingulate sulcus
Subparietal sulcus
Parieto-
occipltal
su tcus
los
the
pal
lim
(Fir
fro
pol
sisl
the
ba<
re€
Th
of
sh(
Pat
enl
Oht
por
anl
latr
ito
die
Rhinal
su I cus
cip
wit
Collateral
su tcus
SUI
Figure.l3-5.
Gyri and sulci on the medial and inferior surfaces of the right
cerebral hemisphere. (A) uncus. (B) lsthmus (retrosplenial corte><) connecting
the cingulate and parahippocampal gyri. ( x 0.63)
orl
co
re(
lan
Occipitotemporal sulcus
Olfactory Olfactory
f;iJ
""0
surcus
Figure-13-6. Gyri and sulci on the inferior surface of the right cerebral
hemisphere. (A) Uncus. (x 0.63)
228
229
Chapter 13: Topography of the Cerebral Hemispheres
losum, is the subcallosal glrus, also known as
the parolfactory area. This is not corto(, but it is
part of the septal area, a component of the
limbic system (see Ch. 18).
On the inferior surface of the hemisphere
(Figs. 13-5 and 13-6), a convolution extends
from the occipital pole almost to the temporal
pole. The posterior part of the convolution consists of the lingual glrus. The anterior part forms
the parahippocampal gtms, which hooks sharply
baclavard on its medial aspect as the uncus, a
region in which fibers of the olfactory tract end.
The collateral sulcus defines the lateral margin
of the lingual and parahippocampal gyti. The
short rhinal sulcus, at the lateral edge of the
parahippocampal gyrus anteriorly, delimits the
entorhinal area, which belongs to the olfactory
and limbic systems. The medial occipitotem'
poral ryrus, which is inconstant in morphology
Lnd broken up by irregular sulci, lies along the
lateral side of the collateral sulcus, The occip'
itotempbral sulcus intervenes between the medial occipitotemporal gyrus and the lateral oc'
cipitotemporal ryrus. The latter is continuous
wittr the inferior temporal gyrus on the lateral
surface of the hemisPhere.
The olfactory bulb and olfactory tract on the
orbitalsurface of the frontal lobe (see Fig. 13-6)
conceal most of the olfactory sulcus' The ryrus
rectus is medial to the olfactory sulcus, and the
large area lateral to the olfactory sulcus consists
of irregular orbital ryri. The cingulate and para-
hippocampal gyri are connected by a narrow
isthmus (retrosplenial corto<) beneath the splenium of the corpus callosum and formthe "lim'
bic lobe" of the cerebral hemisphere, which also
includes the hippocampus. The limbic lobe is
part of the limbic system of the brain, which
incorporates several additional structures, most
'
prominently the dentate gyrus and amygdaloid
body (both in the temporallobe), hypothalamus
(especially the mamillary bodies), septal area,
and anterior and some other nuclei of the
thalamus. The limbic system, which is involved
in memory and certain asPects of behavior, is
described in Chapter 18.
SUGGESTED READING
Bisaria KK: Grooves on the occipital lobe of Indian
brains, J Anat 139t779-582, 1984
Haines'DE: Neuroanatomy. An Atlas of Structures,
Sections and Systems, lrd ed. Baltimore, Urban
& Schwarzenberg, 1991
Montemuno DG, Bruni JE: The Human Brain in
Dissection, 2nd ed. New York, Oxford University hess, 1988
Nieuwenhuys R, Voogd J, van Huijzen C: The Human Central Nervous System. A Synopsis and
Atlas, 3rd ed. Berlin, Springer-Verlag, f 988