278 Neuroanatomy: Draw It to Know It
Cerebral Hemisphere — Inferior Face
Here, we will draw the lobes, g yri, and sulci of the infe-
rior surface of the brain and we will also learn the
anatomy of the Sylvian fi ssure. Draw the undersurface
of the brain, but on one side, leave out the anterior
end of the temporal lobe. Include the following ana-
tomic landmarks: the optic chiasm and neighboring
pituitary body and mammillary bodies, the midbrain,
and cerebellum. Next, in the anterior one third of
the hemisphere, label the frontal lobe. Th en, in the pos-
terior one third of the hemisphere, draw the basal pari-
etotemporal line; anterior to it, label the temporal lobe,
and posterior to it, label the occipital lobe. Finally,
include the collateral sulcus and label the limbic lobe
medial to it.
Now, on the opposite side of the brain, let’s draw the
g yri and sulci. First, within the medial frontal lobe, label
the olfactory sulcus. Medial to it, label the g yrus rectus,
and lateral to it, label the orbital g yri and orbital sulci.
Now, on the medial aspect of the occipital lobe, label the
lingual g yrus, and on the lateral aspect, label the inferior
occipital g yrus. Next, within the temporal lobe, draw the
collateral and occipitotemporal sulci. Medial to the col-
lateral sulcus, label the parahippocampal g yrus, and in
between the collateral and occipitotemporal sulci, label
the fusiform g yrus. Th en, lateral to the fusiform g yrus,
label the inferior temporal g yrus. Next, at the anterior
end of the collateral sulcus, label the rhinal sulcus — the
collateral sulcus either merges with this sulcus or runs in
parallel to it (see Drawing 21-3). Now, show that the
parahippocampal g yrus doubles back onto itself as the
uncus; this is, generally, the fi rst portion of the brain to
herniate over the tentorium cerebellum during uncal
herniation.
Next, let’s draw the anatomic poles of the brain: label
the frontal pole at the anterior end of the frontal lobe;
label the temporal pole at the anterior end of the tempo-
ral lobe; and label the occipital pole at the posterior end
of the occipital lobe.
Now, we will draw the Sylvian fi ssure. First, further
defi ne the region surrounding the optic chiasm as the
anterior perforated substance, which is perforated by
short branches of the proximal middle cerebral artery.
Next, label the internal carotid artery just lateral to the
optic chiasm. Th en, show that the proximal middle cere-
bral artery (the M1 branch) originates from the internal
carotid artery within the cistern of the vallecula cerebri
(aka the carotid cistern) and passes laterally within this
cistern through the deep (or basal) portion of the Sylvian
fi ssure between the frontal and temporal lobes. As the
Sylvian fi ssure wraps around to the lateral convexity of
the brain, the related cisternal space becomes the cistern
of the lateral cerebral fossa; exactly where this cisternal
transition occurs is inconsistently defi ned.^1 , 7 – 11
Now, let’s continue with the lateral face of the Sylvian
fi ssure. Draw an outline of the lateral cerebral hemi-
sphere and include the central sulcus for orientational
purposes. First, draw the anterior-inferior division of the
Sylvian fi ssure; then, at its midpoint, draw a “V” for the
rami extensions from the Sylvian fi ssure. Label the lower
arm of the “V” as the anterior horizontal ramus and the
upper arm as the anterior ascending ramus: the anterior
horizontal ramus runs roughly horizontally and the
anterior ascending ramus runs roughly vertically. Th ese
rami subdivide the inferior frontal g yrus as follows:
beneath the anterior horizontal ramus, label the pars
orbitalis; then, in between the two rami, label the trian-
gular-shaped pars triangularis; and lastly, posterior to
the anterior ascending ramus, label the pars opercularis.
Next, let’s draw the posterior-superior division of the
Sylvian fi ssure. At the distal end of the central sulcus,
draw the horizontally directed posterior horizontal
ramus and then complete the Sylvian fi ssure with the
posterior ascending ramus. Th e supramarginal g yrus caps
this ramus. Note that a posterior descending ramus also
exists, which lies along the vertical plane of the posterior
ascending ramus (we leave it out for simplicity).^1 – 6