638 



PHYSIOLOGY OF THE CEREBRUM 



While the isolation of smaller areas within any larger area, as of the arm or 

 the leg, is not so marked as this localization 'of group areas,, it is nevertheless 

 much sharper than it is in the monkeys; for when contraction is induced by 

 stimulation of a definite point, it is as a rule confined to one definite group 

 of muscles and does not spread as in the monkeys to all or most of the muscles 

 of the same member. 



For purposes of diagnosis the exposed cerebral cortex of man (Figs. 289 

 and 290) has in rare cases been stimulated electrically, and results have been 

 obtained which in general agree with observations based on cortical lesions, 

 as well as with the above-described results on the manlike apes. The motor 



Shoulder 

 Elbow 

 Wrist 



Finger & - 

 Thumb 



f/es """ 



Sufcus centra//* 



Closing mouth 



Opening \ Mastication 

 mouth lfocal cord * 



FIG. 288. The motor cortical areas of the chimpanzee, after Sherrington and Greenbaum. The 

 extent of the motor zone is indicated in black. The red arrows indicate the region in which 

 the special areas are to be found. 



cortical zone of man probably consists therefore of the anterior central con- 

 volution^ the posterior part of the frontal convolutions and the paracentral 

 lobule. Within this zone the areas for lateral movements of the head and 

 eyes are located in the posterior part of the second frontal convolution; the 

 face musculature is represented in the lower part of the anterior central con- 

 volution, the muscles of the upper extremity in the middle part, and those 

 of the lower extremity in the upper part. The paracentral lobule in each 

 hemisphere (Fig. 290) seems to be associated with both opposite extremities. 

 Above the cortical area for the upper extremity is found the area for the 

 musculature of the trunk. 



It is probably not too much to suppose that the smaller areas within each 

 of these larger areas have the same general arrangement as have those of 

 the apes. 



