53 
bo 
THE NERVOUS SYSTEM. 
presents no communication with the other ventricles of the brain. Indeed, the 
term “ventricle,” as applied to it, is quite inappropriate, seeing that at no period in 
the development of the brain has it any connexion with the general ventricular 
system. It is usually stated that it represents a portion of the great longitudinal 
fissure, which has become cut off and walled round about by the growing com- 
missures of the hemispheres, but it is doubtful if this is the case (see p. 555). 
LATERAL VENTRICLE. 
The cavity in the interior of the cerebral hemisphere is called the lateral 
ventricle. It is lined throughout by ependyma continuous with the ependymal 
lining of the third ventricle. In many places the walls of the cavity are in appo- 
sition, whilst in other localities spaces of varying capacity, and containing cerebro- 
spinal fluid, are left between the bounding walls. 
The lateral ventricle (ventriculus lateralis) communicates with the third ventricle 
of the brain by means of a small foramen, just large enough to admit a crow-quill, 
which is termed the foramen of Monro. ‘This aperture is placed in front of the fore 
end of the optic thalamus and behind the anterior pillar of the fornix. 
The highly-irregular shape of the lateral ventricle can be best understood by the 
study of a cast of its interior (Figs. 394: and 379, p.509). It is usual to describe it as 
being composed of a body and 
three horns, viz. an anterior, 
a posterior, and a descending 
horn. The anterior horn is 
that part of the cavity which 
lies in front of the foramen of 
Monro. The body is the por- 
tion of the ventricle which 
extends from the foramen of 
Monro to the splenium of the 
corpus callosum. At this point 
the posterior and descending 
horns diverge from the hinder 
part of the body. The pos- 
terior horn curves backwards 
and inwards into the occipital 
lobe. It is very variable in 
its lenvth and capacity. The 
descending horn proceeds with 
a bold sweep round the hinder 
end of the optic thalamus, and 
then tunnels in a forward and 
inward direction through the 
temporal lobe towards the 
temporal pole. The early foetal 
lateral ventricle is very capa- 
cious and presents an arched 
or semilunar form. It is com- 
NENT. Ill 
INFERIUS 
rite posed of parts which corre- 
Fic, 394.—DRAWING TAKEN FROM A CAST OF THE VENTRICULAR spond to the anterior horn, the 
SYSTEM a THE eRe as seen eo above (after Retzius). body, and the descending horn, 
Vent. III. Third ventricle. Vent. IV. Fourth ventricle. and there is little or no de- 
2.SP. Recessus suprapinealis. ; 
; pial mareation between them. The 
posterior horn is a later production. It comes into existence with the occipital 
lobe and is produced as a diverticulum or elongated pouch, which grows backwards 
from the upper and hinder part (7.e. the convexity) of the primitive cavity. 
Anterior Horn of the Lateral Ventricle (cornu anterius).—The anterior horn 
forms the foremost part of the cavity, and extends in a forward and outward direc- 
tion in the frontal lobe. When seen in coronal section it presents a triangular 
yee 
