4 
LATERAL VENTRICLE. 533 
outline, the floor sloping upwards and outwards to meet the roof at an acute 
angle. It is bounded in front by the posterior surface of the genu of the corpus 
callosum; the roof is also formed by the corpus callosum. The inner wall, which 
is vertical, is formed by the septum lucidum; whilst the sloping floor presents a 
marked elevation 
or bulging, viz. the 
smooth, rounded, 
and prominent 
extremity of the 
pear-shaped caud- 
ate nucleus. 4 
Body of the 
Lateral Ventricle 
(pars centralis).— 
The body of the 
cavity is likewise | 
roofed by the 
corpus callosum. 
On the inner or 
mesial side it is 
bounded by the 
attachment of the 
fornix to theunder 
surface of the cor- 
pus callosum and 
by the hinder part 
of the septum 
/ Great longitudinal fissure 
Corpus callosum (genu) 
Anterior horn of 
lateral ventricle 
Caudate nucleus 
Caudate nucleus 
(in section) 
Corpus callosum (genu) 
Great longitudinal fissure 
tain, Cg ak eae acces AM 
outer side it is 
closed, as in the case of the anterior horn, by the meeting of the floor and the roof 
of the cavity. On the floor a number of important objects may be recognised. 
From without inwards these are met in the following order: (1) the caudate 
nucleus; (2) a groove which extends obliquely from before backwards and outwards 
between the caudate nucleus and the optic thalamus, and in which are placed the 
vein of the corpus striatum and a white band called the tenia semicircularis ; (3) 
a portion of the upper surface of the optic thalamus; (4) the choroid plexus; (5) 
the thin sharp lateral edge of the fornix. 
The caudate nucleus narrows rapidly as it proceeds backwards on the outer part 
of the floor of the body of the lateral ventricle. The vein of the corpus striatum is 
covered over by ependyma. It joins the vein of Galen close to the foramen of 
Monro. The connexions of the tenia semicircularis will be dealt with later. The 
portion of the upper surface of the optic thalamus which appears in the floor of the 
ventricle is in great part hidden by the choroid plexus, which lies upon it. The 
choroid plexus is a rich vascular fringe which appears from under cover of the sharp 
lateral edge of the fornix. In front it is continuous, behind the foramen of Monro, 
with the corresponding choroid plexus of the opposite side, whilst behind, it is 
carried into the descending horn of the ventricle. Although the choroid plexus 
has all the appearance of lying free within the ventricle, it must be borne in mind 
that it is invested by an epithelial layer which represents a portion of the hemi- 
sphere wall and excludes it from the cavity. This thin layer is continuous on the 
one hand with the sharp edge of the fornix, and on the other it is attached to the 
upper surface of the optic thalamus. 
Posterior Horn of the Lateral Ventricle (cornu posterius).—The posterior 
horn is an elongated diverticulum carried backwards into the occipital lobe from the 
hinder end of the body of the ventricle. It tapers to a point and describes a gentle 
curve, the convexity of which is directed outwards. The roof and outer wall of this 
portion of the ventricular cavity are formed by the tapetum of the corpus callosum. 
In coronal sections through the occipital lobe this is seen as a thin but distinct 
layer of white fibres, which lies immediately outside the ependyma and to the inner 
o4 a 
