FUNCTIONS OF THE BRAIN 



953 



sented by separate and special centres ; (2) that stimulation of any 

 one of these areas leads, not to contraction of individual muscles, 

 but to contraction of muscular groups which have to do with the 

 execution of definite movements. 



Sulc.caUoso 

 marg? 



SuLc.parie.to 

 occlp. 



Suk.calcarin. 



C.S S.-rfeJ. 



Fig. 385. ' Motor ' Area on Mesial Surface of Hemisphere: Brain of a Chimpanzee 

 (Troglodytes Niger) (Griinbaum and Sherrington). Left hemisphere: mesial sur- 

 face. The extent of the ' motor ' area on the free surface of the hemisphere is 

 indicated by the black stippling. On the stippled area ' LEG ' indicates that 

 the movements of the lower limb are represented in all the regions of the ' motor ' 

 area visible from this aspect. The minuter subdivisions in this area overlap 

 each other so much that no attempt is made to distinguish them in the diagram. 

 ' Anus and vagina ' indicates the position from which perineal movements can 

 be primarily elicited. Sulc. central. central fissure; Sulc. calcarin. = calcarine 

 fissure; Sulc. parieto occip. =parieto-occipital fissure ; Sulc. calloso fafg.=calloso- 

 marginal fissure ; Sulc. precentr. marg. = precentral marginal fissure. The single 

 italic letters mark spots whence, occasionally and irregularly, movements of the 

 foot and leg (//), of the shoulder and chest (s), and of the thumb and fingers (h), 

 have been evoked by strong faradization. The shaded area marked ' EYES ' 

 indicates a field of free surface of cortex which, under faradization, yields con- 

 jugate movements of the eyeballs. The conditions under which these reactions 

 are obtained separates them from those characterizing the ' motor ' area. 



The Stability of the Reactions obtained by Stimulating Cortical Points. 



The question whether stimulation of a ' motor ' area or point invariably 

 causes the same movements, when it causes any movements at all, has 

 been recently investigated by Graham Brown and Sherrington. They 

 observed the contractions of two isolated antagonistic muscles acting 

 on the elbow- joint (in monkeys) after elimination of all the other 

 muscles of the arm and shoulder by section of their ' motor ' nerves, when 

 a point on the area of the cortex in which the movements of the elbow 

 are represented was excited by the unipolar method. They find that 

 a cortical point which has given flexion at the elbow, sometimes on 



