BASAL GANGLIA OF THE ENCEPHALON. 



607 



called an intraventricular portion, projecting into the anterior part of the 

 lateral ventricles, and an extraventricular portion, which is embedded in the 

 white substance at the base of the brain. 



The optic thalami are oblong bodies situated between the posterior ex- 

 tremities of the corpora striata and resting upon the crura cerebri on the two 

 sides. These are white externally, and in their interior they present a mixt- 

 ure of white and gray matter. 



If a horizontal section be made through the brain, involving the corpora 

 striata and the optic thalami, the corpora striata present a division into two 

 nuclei. These are the 

 caudate nucleus, which 

 is internal, and the 

 lenticular nucleus, 

 which is external to 

 and behind the cau- 

 date nucleus. Exter- 

 nal to the lenticular 

 nucleus, is a band of 

 white substance, called 

 the external capsule, in 

 which there is a band 

 of gray matter, called 

 the claustrum. Exter- 

 nal to the external cap- 

 sule, at its anterior 

 portion, is the insula, 

 or island of Reil. 



Between the cau- 

 date nucleus and the 

 lenticular nucleus in 

 front, is a broad band 

 of white fibres, which 

 is continuous with a 

 band of white fibres 

 lying posteriorly, be- 

 tween the lenticular 

 nucleus and the optic 

 thalamus on either 

 side. This band is the 

 internal capsule. The 

 portion of the internal 

 capsule which lies between the caudate nucleus and the lenticular nucleus is 

 called its anterior division. The portion of the internal capsule situated 

 between the lenticular nucleus and the optic thalamus is its posterior divis- 

 ion. The bend where the posterior division of the internal capsule joins the 

 anterior division is called the knee of the capsule. 



FIG. VSR. Horizontal section of the hemispheres, at the level of the cere- 

 bral ganglia (Dalton). 



1, great longitudinal fissure between the frontal lobes; 2, great longi- 

 tudinal fissure between .the occipital lobes ; 3, anterior part of the 

 corpus callosum ; 4, fissure of Sylvius ; 5, convolutions of the insu- 

 la ; 6, caudate nucleus of the corpus striatum ; 7, lenticular nucleus 

 of the corpus striatum ; 8. optic thalamus ; 9, internal capsule ; 10, 

 external capsule ; 11, claustrum. 



