ix j Intermediate Prcc<iitriil Area '217 



nt homology and at the same time bear in mind how this type of cortex is distributed in the 

 human being. Now as 1 have already mentioned the simian fronto-orbital sulcus is the 

 supposed, and I believe the actual, homologue of the anterior limiting sulcus of the Island 

 of Reil ; this being so, the convolution bounding it in front must be the equivalent of the 

 human orbital operculum : in man the orbital operculum is covered by an " intermediate 

 precentral " type of cortex; in (he ape, therefore, we find a corresponding state of affairs, only 

 our opercular strip of " intermediate " cortex is thrown forwards. Further, the small area of 

 cortex intervening between the superior limiting sulcus of the insula ("anterior Sylvian") 

 and the fronto-orbital sulcus is not enveloped by an "intermediate precentral" type of cortex, 

 because, as Cunningham and others have pointed out, it is homologous with the anterior end 

 of the insula, it is the relic of the exposed insula prevalent in animals lower down in the 

 scale, and the histological examination of its cortex gives full support to this belief. 



FUNCTIONS OF THE "INTERMEDIATE PRECENTRAL" AREA. 



In previous chapters the doctrine of Munk, Bastian, Mott, arid others that the so-called 

 regio Rolandica bears a mixed sensori-motor function has been contested, and allegiance 

 given to the teaching of Ferrier, Schafer, and more recently, Sherrington and Griinbaum, 

 that motion and sensation have separate and independent cortical representation. Similarly 

 in the case of the area which I have denned and called "intermediate precentral," I refuse to 

 believe, as some maintain, that it has a dual function in the narrow sense of the term. 



Turning for a moment to the masterly considerations of Hughlings Jackson, we find it 

 suggested that movement is represented at three levels of the central nervous system. The 

 first or lowest level consists of the cord, medulla and pons, it represents simplest movements. 

 The second or middle level is composed of the " so-called " motor region of the cerebral cortex, 

 it represents complex movements (re-represents). The third or highest level is composed of 

 centres occupying the frontal lobes, it represents most complex movements (re-re-represents). 

 Proof in support of this hypothesis and proof of the strongest character -has been adduced 

 by Hughlings Jackson himself, and the evidence gathered in the years which have passed since 

 his view was expressed, only necessitates slight modifications, without in the least affecting 

 its main basis. One modification which I would suggest concerns localisation and receives 

 justification in some observations set forth here and elsewhere ; it is that instead of localising 

 the middle or second level in the old "motor region," which embraced the whole Rolandic 

 zone, I would place it in the restricted area which I believe to have structural characters of an 

 essentially motor kind, and to which I have given the name "precentral." Now if we regard 

 the "precentral" area proper as the "middle or second level," I think that more can be said 

 in accordance with Hughlings Jackson's reasoning, and I will submit that the " intermediate 

 precentral " cortex, now under consideration, forms a very important part (I should be going 

 beyond bounds if I said the whole) of " the highest or third level." I am of opinion that this 

 particular stretch of cortex is specially designed for the execution of complex movements of 

 an associated kind, of skilled movements, of movements in which consciousness or volition takes 

 an active part, as opposed to automatic movements, and my remarks will now be devoted to 

 the development of this thesis. 



First, looking at the area from the histologist's point of view. Not only is it deposited 

 in close relation to the "precentral," or as we may now call it the "primary" cortical motor 

 area, but it possesses structural characters which betoken physiological kinship. Thus in 



C. 28 



