INTERIOR OF THE CEREBIU'M. 



663 



its outer surface, corresponding to the convolutions and sulci of the island of Reil, 

 from which it is separated by a thin white lamina. 



Upon making a transverse vertical section through the middle of the nucleus 

 lenticularis it is seen to present two white lines, parallel with its lateral border, 

 which divide it up into three zones, of which the outer and largest is of a reddish 

 color, and is known as the putamen, while the two inner are paler and of a yellowish 

 tint, and are termed the globus pallidus. All three zones are marked by fine 

 radiating white fibres, which are most distinct in the putamen. The gray matter 

 of the corpus striatum is traversed by nerve-fibres, some of which are believed to 

 originate in it. The cells are multipolar, both large and small ; those of the 

 lenticular nucleus containing yellow pigment. 



FIG. 355. Middle part of a horizontal section through the cerebrum at the level of the dotted line in the 

 small figure of one hemisphere. (From Ellis, afier Dalton.) 



The internal capsule is formed by fibres of the crusta of the crus cerebri, 

 supplemented by fibres derived from the corpus striatum and optic thalamus on 

 each side. In horizontal section (Fig. 355) it is seen to be somewhat abruptly 

 curved, with its convexity inward : the prominence of the curve is called the genu, 

 and projects between the caudate nucleus and the optic thalamus. The portion in 

 front of the genu is termed the anterior limb, and separates the lenticular from the 

 caudate nucleus ; the portion behind the genu is the posterior limb, and separates 

 the lenticular nucleus from the optic thalamus. The internal capsule is composed 

 largely of fibres, which, derived from the crusta of the crus cerebri, are continued 

 through it to the cortex of the cerebral hemispheres, the fibres of the anterior 

 limb passing to the frontal region ; those from the genu and the anterior two-thirds 

 of the posterior limb pass to the Rolandic area of the cortex, while those in the 



