THE FORE-BRAIN 



593 



more extended region than the Rolandic area of the human 1 train ; 

 this he terms the ceutro-parietal region, which includes, in addition 

 to the two central convolutions and the supramarginal gyrus, the 

 anterior part of the upper and lower parietal lohes. Within this 

 extensive centro-parietal region lie both the cortical terminations 

 of the neurones of cutaneous and muscular sensibility and the 

 nerve-cells in which voluntary movement is initiated. But the 

 sensory elements are not completely mingled with the motor ; 



POT 



V- 



Fn 



t. 300. Plan of projection and association centres. (After Flechsig.) N/-.', sriisory-motor area ; 

 I", visual area; A, auditory area; F, frontal association area; /, association area of insula; 

 POT, parieto-occipito-temporal association area ; 0, olfactory area. 



the former extend more particularly' behind the central sulcus, the 

 latter lie almost completely in front of it. 



This theory agrees fairly well with Flechsig's observations, 

 which are founded on the myelination of the projection fibres of 

 the corona radiata during embryonic development and the first 

 months of extra-uterine life. He states that the centro-parietal 

 zone extends backward to the posterior border of the post-central 

 convolution and the paraceiitral lobule; forward, to the frontal 

 convolutions, reaching the operculum below, and the corpus 

 callosum at the medial surface (Figs. 299, 300). According to 

 Flechsig, the origins of the pyramidal tracts do not spring 

 uniformly from the whole of this centro-parietal zone and in 



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