ON VOLUNTAKY MOVEMENTS. 665 



frog, on the one hand, and the more highly developed monkey on the other ; 

 and that is one reason why we have taken the dog first and dwelt so long 

 upon it. In the rabbit, a similar localization may be observed, but far less 

 definite, far more diffuse ; it becomes still less in the bird, and is hardly 

 recognizable in the frog. It will not be profitable to dwell on the details of 

 the phenomena of these lower animals; but the phenomena of the monkey, 

 leading up as they do to those of man, call for special notice. 



568. When in a monkey, in an individual, for instance, belonging to 

 the genus Macacus, the surface of the cerebrum is 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 (ef. Fig. 148), movements 

 of the fore limb follow. The "motor area for the fore limb" thus discov- 

 ered is more circumscribed and definite than is the corresponding area in 

 the dog. Its outline (Fig. 149) is roughly that of a truncated triangle bi- 

 sected 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 intra-parietal 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 shows that the 

 whole area is divided into areas corresponding to movements of particular 

 parts of the forearm, 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. 149) ; if the elec- 

 trodes be shifted ventrally, movements of the elbow make their appear- 

 ance ; 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 upward toward the mesial 

 line; the thumb is moved first, then the forefinger, 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 appropri- 

 ate segment of the limb, in other parts extension, in certain parts abduc- 

 tion, in other parts adduction, and so on. 



Similar exploration shows 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. 

 150). Within this general area for the hind limb we may similarly distin- 

 guish special areas for the hip (Figs. 149, 150) in the front portion, for the 

 knee and ankle behind this, and for the digits still further backward, the 

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

 dig-its. 



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

 face, dipping down into the mesial surface along the marginal convolution 

 (Fig. 150) and reaching laterally on the lateral dorsal surface to the dorsal 

 extremity of the precentral sulcus (Fig. 149), is the "area for the head," 

 that is to say, for the movements of the head brought about by contractions 

 of the muscles of the neck. 



Ventral to this again, in front of the precentral sulcus, is the " area for 

 the eyes," that is to say, for contractions of the ocular muscles ; and behind 



