134 HUMAN PHYSIOLOGY. 



however, remaining united, ascend higher and terminate in the paracentral 

 lobule, the superior extremity of the ascending frontal and parietal convo- 

 lutions. The sensory tract can be traced upward, through the posterior 

 third, into the cerebrum, where they probably terminate in the hippo- 

 campus major and unciate convolution. 



Functions. The Corpora striata are the centres in which terminate 

 some of the fibres 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 anatomical relations, that they 

 are motor centres. Irritation by a weak galvanic current produces mus- 

 cular 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 fibres of the anterior two- 

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

 them from their trophic centres in the cortical motor region, a descending 

 degeneration is established, which involves the direct pyramidal tract of 

 the same side and the crossed pyramidal 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 receives the fibres of the tegmentum, 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 in some way connected with sensation. In both cases 

 their action is crossed. 



CEREBELLUM. 



The Cerebellum is situated in the inferior fossae of the occipital bone, 

 beneath the posterior lobes of the cerebrum. It attains its maximum 

 weight, which is about 5 ozs., between the twenty-fifth and fortieth years ; 

 the proportion between the cerebellum and cerebrum being I to 8. 



It is composed of two lateral hemispheres and a central elongated lobe, 

 the vermiform process ; the two hemispheres are connected with each other 

 by the fibres of the middle peduncle forming the superficial portion of the 



