CHAP. IL] THE BRAIN. 1039 



explored with reference to the effects of electric stimulation, it is 

 found that when the current is applied to the precentral or 

 ascending frontal and the post-central or ascending parietal 

 convolutions which lie respectively in front of and behind the 

 important central fissure or fissure of Rolando (cf. Fig. 125), 

 movements of the fore limb follow. The 'motor area for the 

 fore limb ' thus discovered is more circumscribed and definite than 

 is the corresponding area in the dog. Its outline (Fig. 126) is 

 roughly that of a truncated triangle bisected by the central 

 fissure, with the broad base at some distance from the mesial 

 line, and the truncated apex reaching on the lateral surface of the 

 hemisphere to a well-marked bend in the lower part of the central 

 fissure. Behind, it reaches as far as the intraparietal fissure which 

 somewhat sharply defines its hind border, and in front it ceases no 

 less definitely at some little distance behind the precentral fissure. 

 Further examination shews that the whole area is divided into 

 areas corresponding to movements of particular parts of the fore 

 arm, and that these are arranged in a definite relation to each 

 other. In the more dorsal part of the area, at the base of the 

 triangle, stimulation produces movements of the shoulder 

 (Fig. 126) ; if the electrodes be shifted ventrally movements 

 of the elbow make their appearance ; if still more ventrally, 

 movements of the wrist come in, and these are in turn succeeded 

 ventrally by movements of the digits generally, of the forefinger, 

 and lastly of the thumb. A very striking experiment may be 

 made by applying a current of suitable strength, first at the lower, 

 ventral border of the area, and then gradually advancing upwards 

 towards the mesial line ; the thumb is moved first, then the fore- 

 finger, then the rest of the digits, then the wrist, next the elbow, 

 and lastly the shoulder. Further, in certain parts of the area the 

 resulting movement is flexion of the appropriate segment of the 

 limb, in other parts extension, in certain parts abduction, in other 

 parts adduction, and so on. 



Similar exploration shews that the "area for the hind limb," 

 lies on the median side of the area for the fore limb, stretching 

 besides on to the mesial surface along the marginal convolution 

 which forms the dorsal portion of the wall of the great longitudinal 

 fissure ; it reaches as far back as the intra-parietal sulcus, and is 

 succeeded in front by the "area for the trunk" (Fig. 127). Within 

 this general area for the hind limb we may similarly distinguish 

 special areas for the hip (Figs. 126, 127) in the front portion, for 

 the knee and ankle behind this, and for the digits still farther 

 backwards, the area for the great toe being however in front of 

 the area for the other digits. 



In front of the areas for the limbs and trunk, on the median 

 dorsal surface, dipping down into the mesial surface along the 

 marginal convolution (Fig. 127) and reaching laterally on the 

 dorsal lateral surface to the dorsal extremity of the precentral 



F. 66 



