l8o HUMAN PHYSIOLOGY. 



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 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 in tra ventricular 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 trans- 

 verse striations, from the intermingling of white fibers and gray cells. 



The optic thalami are two oblong masses situated in the ventricles poster- 

 ior to the corpora stiata, 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, rom 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 posterior surface of the lenticular nucleus. These 

 two segments unite at an obtuse angle, which is directed toward the 

 median line. Pathologic observation has shown that the nerve-fibers 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, however, remaining united, ascend higher 

 and terminate in the paracentral lobule, and in the ascending front con- 

 volution. Those of the sensor tract can be traced upward, through the poster- 

 ior third, into the cerebrum, where they probably terminate in the ascending 

 parietal and the superior parietal convolutions and in the gyrus fornicattis. 



Functions. The corpora striata are the centers in which terminate some 

 of the fibers of the superficial or motor tract of the crura cerebri ; others pass 

 upward through the internal capsule, to be distributed to the cerebrum. 

 It might be inferred, from their anatomic relations, that the corpora striata 



