Section passes through chiasma opticum, and is viewed from in front.
_1_, Longitudinal fissure; _2_, septum pellucidum; _3_, columns
(anterior pillars) of fornix; _4_, lateral ventricle; _5_, chorioid
plexus; _6_, corpus medullare (central white matter) of hemisphere;
_7_, caudate nucleus; _8_, lenticular nucleus; _9_, internal
capsule; _10_, external capsule; _11_, insula.
]
The =lateral ventricle= (Ventriculus lateralis) is the irregular cavity
in the interior of each cerebral hemisphere.[201] Each communicates with
the third ventricle through the =interventricular foramen= (of Monro),
and by a small canal with the cavity of the olfactory bulb. It is usual
to describe the ventricle as consisting of three parts, viz., the
central part or body, and anterior and inferior horns. The =anterior
horn= (Cornu nasale) is the part in front of the interventricular
foramen; it communicates ventrally with the olfactory cavity. The
=central part= (Pars centralis) extends back to the splenium of the
corpus callosum. It opens into the third ventricle through the
interventricular foramen, which is situated between the fornix and the
anterior part of the thalamus. The =inferior horn= (Cornu ventrale)
curves downward and forward into the pyriform lobe. The roof of the
ventricle is formed by the corpus callosum and the inner wall is the
septum pellucidum. After removal of the roof the floor is seen to be
formed chiefly by two bodies. The anterior one is the =caudate nucleus=
(Nucleus caudatus), a somewhat pear-shaped gray eminence, the long axis
of which is directed obliquely upward, backward, and outward. Its
anterior large end is termed the head, and the posterior long tapering
end the tail. The posterior body, the =hippocampus=, is white on its
ventricular surface, which is strongly convex. It curves outward and
backward and then turns downward and forward to join the pyriform lobe.
The two bodies are separated by an oblique groove which is occupied by
the =chorioid plexus= of the lateral ventricle. This is the thickened
edge of a fold of pia mater, the tela chorioidea (or velum
interpositum), which lies between the hippocampus and the thalamus. It
contains convolutions of small blood-vessels and in old subjects there
may be calcareous concretions in it. The plexuses of the two sides are
continuous through the interventricular foramen. On drawing the chorioid
plexus backward a narrow white band, the =stria terminalis= (or tænia
semicircularis), is seen along the margin of the caudate nucleus, where
it bounds the intermediate groove. The plexus partially covers a wider
white band which is blended with the white substance of the hippocampus;
this is the =posterior pillar of the fornix= and its continuation, the
=fimbria=.
[Illustration: