476 THE BKAIN. 



sisting of bundles of ascending fibres derived from the crura cerebri. 

 The anterior and more internal of the two parts into which the corpus 

 striatum is thus divided is the caudate nucleus ( 7 ), so called because a 

 horizontal section through its uppermost portion exhibits a slender, 



Fig. 157. 



HORIZONTAL SECTION OF THE HUMAN BRAIN, at the level of the cerebral ganglia. 

 1, 2. Anterior and posterior portions of the great longitudinal fissure. 3, 4. Anterior and 

 posterior parts of the corpus callosum. 5. Fissure of Sylvius. 6. Beginning of the convolu- 

 tions of the Island of Reil. 7, 8. Corpus Btriatum. 7. Caudate nucleus. 8. Lenticular 

 nucleus. 9. Optic thalamus. 10. Internal capsule. 11. External capsule. 12. Claustrum. 



tail-like prolongation in a backward direction ; the posterior and more 

 lateral part is called the lenticular nucleus ( s ), from its having, in a 

 section at its mid-level, a tolerably regular lens-like figure. Both the 

 optic thalamus and the corpus striatum are traversed b.y slender bundles 

 of fibres, visible to the naked eye, and which have a generally radiating 

 direction upward and outward. 



The outer surface of the lenticular nucleus is inclosed by a thin layer 

 of white substance, the external capsule (n), in which is also to be 

 seen a very narrow band of isolated gray substance, termed the " claus- 

 trum" ( 12 ). At this situation the layer of gray substance at the bottom 

 of the fissure of Sylvius is separated from the corpora striata by only a 

 very narrow interval ; and the fibres running outward and downward 



