THE NERVOUS SYSTEM. 189 
are the most anterior of the basal ganglia and are somewhat 
pear-shaped, the larger ends being craniad and nearer the 
median line than the caudal portions, which curve laterad 
around the optic thalami (Fig. 96). They form a part of 
the floor of the lateral ventricles, and are pierced by the 
anterior commissure (Fig. 98), a small cord of white fibers. 
The corpus striatum consists of both white and gray 
matter. The latter, composed of cells, is disposed in two 
chief nuclei or masses, known as the nucleus caudatus, 
lying anterior and nearer the median line than the nucleus 
lenticularis, which is more lateral and caudal (Fig. 98). 
Fic. 98. Cross-SECTION OF THE BRAIN THROUGH THE ANTERIOR Com- 
MISSURE. 
an, Arachnoid; ce, external capsule; cl, corpus callosum; cm, anterior 
commissure; frc, falx cerebri; f, great longitudinal fissure; fx, 
anterior pillars of the fornix; ic, internal capsule; n, radiating 
fibers of callosum; in, septum lucidum; nc, nucleus caudatus of 
corpus striatum; /, nucleus lenticularis; p, pia mater; v/s, superior 
longitudinal sinus; vz, third ventricle; v, lateral ventricle. 
The center of the nucleus lenticularis is laterad of the optic 
thalamus and dorsad of the crus cerebri. A thin layer of 
white matter, the Jamina semicircularis, separates the optic 
thalamus from the nucleus caudatus. A few fibers from 
the cerebral peduncles form the lamina semicircularis, whose 
edge may be seen in the floor of the lateral ventricle on the 
lateral boundary of the nucleus caudatus. A group of 
