LOCALISATION OF FUNCTION. 26 1 



proportion of the convex surface of a hemisphere is 

 devoted to the control of the muscles whose sense organ 

 is the skin, and in the second place, this area extends 

 on to the mesal surface of the hemispheres. If we com- 

 pare with this the arrangement in the brain of the orang, 

 we find the motor areas in question more concentrated 

 about the central fissure, or fissure of Rolando (the long 

 fissure on either side of which they are seen to lie in 

 Figs. 55 and 56). 



Comparing the arrangement in the monkey with that 

 in the orang, it is found that the proportion of the 

 cerebral cortex devoted to these areas is smaller in the 

 orang, and that within the larger areas, at least, there 

 are spots the stimulation of which does not yield any 

 reaction. The experimental determination of these 

 areas made on the brain of man are of course few in 

 number. So far as they go, they indicate that in this 

 respect the human brain shows an increase in the con- 

 centration and isolation of these areas, and of the centres 

 within them. There is certainly no more important 

 feature of the whole subject of localisation than this 

 concentration in man and the higher apes, but it may 

 be for the moment disregarded while the characters 

 which these areas have in common are first described. 



As might be expected, the homologous portions of 

 the cortex in man and the apes are occupied by similar 

 centres. The motor regions, for example, are grouped 

 in all cases about the central fissure. The area for vision 

 is in the occipital lobe, and that for hearing in the tem- 

 poral. Not only does this general distribution show 

 similarities with that in other mammals, but the simi- 

 larities extend to many details. 



The areas for the different portions of the body are so 

 distributed in the motor cortex that those controlling 

 the muscles of the head and neck lie most anteriorly, 



