CORPORA STRIATA AND OPTIC THALAMI. 199 



duces a temporary loss of power of the opposite side of the body, 

 and a tendency to mo.ve around an axis is manifested, as after 

 a section of one crus cerebri, which, however, may be due to giddi- 

 ness and loss of sight. 



They also assist in the coordination of the complex movements of 

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

 of accommodation. 



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 embedded in the white matter, the smaller portions pro- 

 jecting into the anterior part of the lateral ventricle. Each striated 

 body is divided, by a narrow band of white matter, into two por- 

 tions viz. : 



1. The caudate nucleus, the intraventricular portion, which is conic 

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

 like process. 



2. The lenticular nucleus, embedded 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 fibers and 

 gray cells. 



The optic thalami are two oblong masses situated in the ven- 

 tricles posterior to the corpora striata, and resting upon the posterior 

 portion of the crura cerebri. The internal surface, projecting into 

 the lateral ventricles, is white, but the interior is grayish, from a 

 commingling of both white fibers 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, curved tract of white matter, 

 and is, for the most part, an expansion of the motor tract of 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 



