THE FOKE-BKAIN 



593 



more extended region than the Rolandic area of the human brain ; 

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

 to the two central convolutions and the supramarginal gyrus, the 

 anterior part of the upper and lower parietal lobes. 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 



FK;. 300. Plan of projection and association centres. (After Flechsig.) SE, sensory-motor area ; 

 V, 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 particular!}^ 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 paracentral lobule ; forward, to the frontal 

 convolutions, reaching the operculum below, and the corpus 

 callosurn 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 



VOL. Ill 2 Q 



