32 THE NERVOUS SYSTEM 



matter, which is known as the external capsule. The lentiform 

 nucleus^ which resembles a biconvex lens in shape, is com- 

 pletely embedded in the substance of the cerebral hemisphere, 

 and its medial surface is in contact with a broad band of white 

 matter, termed the internal capsule. As seen in a horizontal 

 section the internal capsule consists of two limbs which 

 meet one another at a bend or genu. The shorter anterior 

 limb lies between the lentiform nucleus and the head 

 of the caudate nucleus, by which it is separated from the 

 anterior part of the lateral ventricle; the longer, posterior 



) Caudate nucleus 

 , -"^^ Corpus callosum 

 Lateral ventricle 

 m>-' Internal capsule 

 - "***T J- _. - - Thalamus 

 Island (of Reil) " 

 Claustrum ' ' 

 External capsule 

 entiform nucleus 



FIG. 19. Frontal (Coronal) Section through Left Cerebral Hemisphere. 



limb is closely applied to the lateral aspect of the thalamus 

 (Fig. 1 8). 



In a Frontal (Coronal) Section made through the cerebral 

 hemisphere opposite the anterior perforated substance (spot), 

 the island, the claustrum, and the external capsule can all be 

 readily identified (Fig. 19). When the lentiform nucleus is 

 examined in such a section, its lower part is seen to become 

 continuous with the grey matter of the anterior perforated 

 substance, and, consequently, the arteries which enter the 

 brain at this point at once come into relationship with the 



