346 



AN INTRODUCTION TO ZOOLOGY 



borne in mind, however, that it is not a true fissure, and simply 

 represents an artificial slit made by tearing away that part of the 

 ventricular wall. 



The corpus striatum is composed of two ganglionic masses 

 of grey matter, an inner and an outer. The inner portion is termed 

 the nucleus caudatus, and it projects far into the floor of the an- 

 terior cornu of the ventricle as a pear-shaped body with the larger 

 end in fiont and the hinder smaller end passing backwards into 

 the descending horn. The outer, somewhat smaller part of the 

 corpus is the nucleus lenticularis, and the two nuclei are separated 



CR 



CC 



EC 



>CS 



1C 



FIG. 1 20. Transverse section of cerebral hemispheres in region 

 of corpus striatum. 



C., claustrum ; C.C., corpus callosum ; Ce., cerebral cortex ; C.R., corona radiata ; C.S., corpus 

 striatum ; B.C., external capsule ; I.C., internal capsule ; L.F., longitudinal fissure ; L.V., lateral 

 ventricle ; N.C., nucleus caudatus ; N.L., nucleus lenticularis ; S.L., septum lucidum. 



by a band of white matter, the internal capsule, which passes 

 upwards around the side of the lateral ventricle into the corona 

 radiata. A similar band of white matter, the external capsule, runs 

 up on the outside of the lenticular nucleus also to join the corona. 

 Along the outer border of the external capsule is a narrow 

 band of grey matter, the claustrum. The corpus callosum, as 

 we have seen, is a broad sheet of transversely running^white fibres 

 passing from one hemisphere to the other. It continues on into the 

 corona, and thence its fibres are distributed in radiating strands to 

 all parts of the cerebral cortex. At the front end it bends sharply 



