THE CENTRAL NERVOUS SYSTEM 



845 



sent physiological 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. 



The arrangement of the various regions follows very closely 

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



Anu3 fj vagina. 



Abdomen 



.Cheat 



SuZciLs, centroUs. 



Mastication 

 FIG. 351. 'MOTOR' AREA OF CORTEX OF CHIMPANZEE (GRUNBAUM AND 



Voca.i 

 cords. 



SHERRINGTON). 

 Lateral aspect of the hemisphere. 



the organs whose nerves come off lowest down are represented 

 highest up in the ' motor ' area. Figs. 351, 352 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 deviation 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, 



