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). 



an 



FIG. 98. CROSS-SECTION OF THE BRAIN THROUGH THE ANTERIOR COM- 

 MISSURE. 



an, Arachnoid; ce, external capsule; cl, corpus callosum; cm, anterior 

 commissure; jxc, falx cerebri; /, 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 ; I, nucleus lenticularis ; p, pia mater ; vis, superior 

 longitudinal sinus ; vn, 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 lamina 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 



