200 HUMAN PHYSIOLOGY. 



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 frontal convolution. Those of the sensor tract can 

 be traced upward, through the posterior third, into the cerebrum, 

 where they probably terminate in the ascending parietal and the 

 superior parietal convolutions and in the gyrus fornicatus. 



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 dis- 

 tributed to the cerebrum. It might be inferred, from their anatomic 

 relations, that the corpora striata are motor centers. Irritation by a 

 weak galvanic current produces muscular movements of the opposite 

 side of the body ; destruction of their substance by a hemorrhage, 

 as in apoplexy, is followed by a paralysis of motion of the opposite 

 side of the body, but there is no loss of sensation. When the 

 hemorrhagic destruction involves the fibers of the anterior two 

 thirds of the posterior segment of the internal capsule, and thus 

 separates them from their trophic centers in the cortical motor 

 region, a descending degeneration is established, which involves 

 the direct pyramidal tract of the same side and the crossed pyra- 

 midal tract of the opposite side. 



Destruction of the posterior one third of the posterior segment 

 of the internal capsule is followed by a loss of sensation on the 

 opposite side of the body and a loss of the senses of smell and vision 

 on the same side (Charcot). The precise function of the corpora 

 striata is unknown, but they are in some way connected with motion. 



The optic thalami receive the fibers of the tegmentus, the posterior 

 portion of the crura cerebri. They are insensible and inexcitable 

 to direct irritation. Removal of one optic thalamus, or destruction 

 of its substance by disease or hemorrhage, is followed by a loss 

 of sensibility of the opposite side of the body, but there is no loss 

 of motion ; their precise function is also unknown, but they are in 

 some way connected with sensation. In both cases their action is 

 crossed. 



