846 



A MANUAL OF PHYSIOLOGY 



in the leg area, the hip, knee, and ankle joints, and the great 

 toe, are represented 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. 

 Inhibition from the Cortex. Contraction is not the only effect 



Sult.CentraL 



Sutc.caHoso 

 marg.- ^ 



Suic.parUto 

 occlp. 



C.S 5. did. 



FIG. 352. 'MOTOR' AREA ON MESIAL SURFACE OF HEMISPHERE: BRAIN OF 

 A CHIMPANZEE (TROGLODYTES NIGER) (GRUNBAUM AND SHERRINGTON). 



Left hemisphere : mesial surface. 



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. centr al. = central fissure ; Sulc. calcarin. = calcarine fissure ; Sulc. parieto 

 occ. = parieto-occipital fissure; Sulc. calloso wayg. = 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 

 (ff), 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 conjugate move- 

 ments of the eyeballs. The conditions under which these reactions are obtained 

 separates them from those characterizing the ' motor ' area. 



on the muscles which can be elicited by stimulating the cortex. 

 Cortical inhibition of tonus and of active contraction is just as 

 characteristic, though not so obvious a result. There is abundant 

 evidence, some of which has previously been alluded to (p. 838), 

 of reciprocal innervation of volitional movements from the 



