THE FOBE-BEAIN 



589 



parts. This shows that even if the electrical method is a 

 valuable means of localising the foci of maximal excitability it is 

 worthless for defining the total area of each centre. These areas 

 probably radiate out from the foci, overlapping and partially 

 fusing with the adjacent centres of other regions of the body, so 

 that it is impossible to destroy them separately. 



Lastly, it must be noted as a serious objection to Munk's 

 theory that the paralytic phenomena which he described are 

 transient and disappear almost completely in a few weeks, even 

 when the cortex has been entirely removed from the corresponding 

 sensory regions. How are we to explain this fact without 



FIG. 298. Sensory-motor area of human cerebral cortex. The cortex of the paracentral lobe of the 

 mesial surface, which is not visible in the figure, also forms part of the sensory-motor area. 



admitting the existence of other sub -cortical centres, able 

 vicariously to assume the psychical functions of the centres that 

 have been destroyed ? But if this theory be accepted, Munk's 

 hypothesis, which confines all psychical functions to the cortex, is 

 overthrown. 



One point remains : granting the mixed sensory and motor 

 character of the excitable area of the cortex, are we to assume 

 that in this area the sensory elements are completely mingled 

 with the motor as first suggested by Tamburini in 1876, or are 

 they partially mingled and partially separate ? 



The localisation in the human brain of that area of the cortex 

 which is in relation with voluntary movement is dependent more 

 on a series of clinical and anatomo-pathological observations than 

 on electrical stimulation of the cortex. Many reliable authors 



