below on _Comparative Anatomy_. In the sulcus between the
corpus callosum and the limbic lobe a narrow band of fibres called the
_cingulum_ is seen, most of its fibres only run a short distance in it
and link together adjacent parts of the brain. If the corpus callosum
be now cut through on each side of its mesial line, the large cavity
or _lateral ventricle_ in each hemisphere will be opened into.

[Illustration: From Cunningham, _Text-The book of Anatomy_.

FIG. 11.--The Gyri and Sulci on the Mesial Aspect of the Cerebral
Hemisphere, r, Fissure of Rolando. r, o, Rostral sulcus. i, t,
Incisura temporalis.]

The lateral ventricle is subdivided into a _central space_ or body,
and three bent prolongations or _cornua_; the _anterior cornu_ extends
forward, outward and downward into the frontal lobe; the _posterior
cornu_ curves backward, outward and inward into the occipital lobe;
the _descending cornu_ curves backward, outward, downward, forward
and inward, behind and below the optic thalamus into the
temporo-sphenoidal lobe. On the floor of the central space may be seen
from before backward the grey upper surface of the pear-shaped caudate
nucleus of the _corpus striatum_ (figs. 12 and 13, f), and to its
inner and posterior part a small portion of the _optic thalamus_,
whilst between the two is the curved flat band, the _taenia
semicircularis_ (figs. 12 and 13, g). Resting on the upper surface of
the thalamus is the vascular fringe of the velum interpositum, named
_choroid plexus_, and immediately internal to this fringe is the free
edge of the white _posterior pillar of the fornix_. The anterior cornu
has the anterior end of the corpus striatum projecting into it. The
posterior cornu has an elevation on its floor, the _hippocampus minor_
(fig. 12, n), and between this cornu and the descending cornu is the
elevation called _eminentia collateralis_, formed by the collateral
fissure (fig. 12, o).

[Illustration: FIG. 12.--To show the Right Ventricle and the left half
of the Corpus Callosum.

a, Transverse fibres, and
b, Longitudinal fibres of corpus callosum.
c, Anterior, and
d, Posterior cornua of lateral ventricle.
e, Septum lucidum.
f, Corpus striatum.
g, Taenia semicircularis.
h, Optic thalamus.
k, Choroid plexus.
l, Taenia hippocampi.
m, Hippocampus major.
n, Hippocampus minor.
o, Eminentia co