690 



PHYSIOLOGY. 



observed in clinics from pathological lesions located and circumscribed 

 in various points of the same hemispheres. 



Some years ago all physiologists admitted the complete inexcita- 

 bility of the cortical substance of the cerebral hemispheres. Accord- 

 ing to the view then held, mechanical, thermal, chemical, and elec- 

 trical irritation of the convolutions did not determine phenomena of 

 any kind. 



& thumb. 



cortfa. 



Fig. 279. The Motor Area and its Subdivisions on the Lateral 

 Aspect of the Hemicerebrum of the Chimpanzee. (GRUNBAUM and 

 SHERBINGTON. ) 



Later, however, it was demonstrated that very slight electrical 

 currents applied to the cerebral convolutions in dogs determined vari- 

 ous movements in the head, limbs, eyes, etc. By this means the 

 operator can cause the execution of various movements to suit his 

 will, as, for example, closing the fist, extending the arm, moving the 

 leg, eyes, face-muscles, etc. These results were best demonstrated in 

 experiments upon apes. By experiments along this line it has become 

 feasible to fix the seat of various cortical motor centers of the brain. 

 In man himself experiments with electricity have been made upon the 

 convolutions exposed for various causes. 





