FUNCTIONS OF THE BRAIN 



gig 



sharp, but shades off somewhat gradually into inexcitable cortex. 

 The sulci in this region cannot be considered to represent physio- 

 logical boundaries, and they vary so much in these higher brains, 

 that they can easily prove fallacious landmarks. On the mesial 

 surface of the hemisphere the ' motor ' area does not extend quite 

 to the calloso-marginal fissure. 



Within this area are localized movements of the leg and arm and 

 their various joints, of the head, face, mouth, tongue, ear, nostril, 

 and vocal cords, of the neck, chest, and abdominal wall, of the pelvic 

 floor, and the anal and vaginal orifices. 



Abdomen 



Chest 



SuZcus centralis. 



CS5.de/. 



Fig. 369. ' Motor ' Area of Cortex of Chimpanzee (Grlinbaum and Sherrington). 

 Lateral aspect of the hemisphere. 



The arrangement of the various regions follows very closely the 

 order of the cranio-spinal nerves, which supply them, but the organs 

 whose nerves come off lowest down are represented highest up in 

 the ' motor ' area. Figs. 369, 370 will make this clear. In the frontal 

 region, isolated from the ' motor ' area by a strait of inexcitable 

 cortex, lies an area the stimulation of which causes conjugate devia- 

 tion of the eyes. But the reaction differs from that obtained on 

 excitation of the ' motor ' area proper in front of the Rolandic fissure. 



It is to be particularly noted (i) that within the larger areas, such 

 as those of the arm and leg, smaller foci can be mapped off which 

 are related to movements of the separate joints thus, in the leg 

 area, the hip, knee, and ankle-joints, and the great toe, are repre- 



