CORPORA STRIATA AND OPTIC THALAMI. 133 



fested, as after a section of one crus cerebri, which, however, may be due 

 to giddiness and loss of sight. 



They also assist in the coordination of the complex movements of the 

 eye, and regulate the movements of the iris during the movements of 

 accommodation for distance. 



CORPORA STRIATA AND OPTIC THALAMI. 



The Corpora Striata are two large ovoid collections of gray matter, 

 situated at the base of the cerebrum, the larger portions of which are 

 imbedded in the white matter, the smaller portions projecting into the 

 anterior part of the lateral ventricle. Each striated body is divided, by a 

 narrow band of white matter, into two portions, viz : 



1. The Caudate nucleus, the intraventricular portion, which is conical 

 in shape, having its apex directed backward, as a narrow, tail-like process. 



2. The Lenticular mtcleus, imbedded in the white matter, and for the 

 most part external to the ventricle; on the outer side of the lenticular 

 nucleus is found a narrow band of white matter, the external capsule; 

 and between it and the convolutions of the island of Reil, a thin band of 

 gray matter, the claustrum ; the corpora striata are grayish in color, and 

 when divided present transverse striations, from the intermingling of white 

 fibres and gray cells. 



The Optic Thalami are two oblong masses situated in the ventricles 

 posterior to the corpora striata, and resting upon the posterior portion of 

 the crura cerebri. The internal surface projecting into the lateral ven- 

 tricles is white, but the interior is grayish, from a commingling of both 

 white fibres and gray cells. Separating the lenticular nucleus from the 

 caudate nucleus and the optic thalamus, is a band of white tissue, the 

 internal capsule. 



The internal capsule is a narrow, bent tract of white matter, and is, for 

 the most part, an expansion of the motor tract o/ the crura cerebri. It 

 consists of two segments, an anterior, situated between the caudate 

 nucleus and the anterior surface of the lenticular nucleus, and a posterior, 

 situated between the optic thalamus and the posterior surface of the len- 

 ticular nucleus. These two segments unite at an obtuse angle, which is 

 directed toward the median line. Pathological observation has shown 

 that the nerve fibres of the direct and crossed pyramidal tracts can be 

 traced upward through the anterior two-thirds of the posterior segment, 

 into the centrum ovale, where, for the most part, they are lost ; a portion, 



