108 Summary [CHAP. 



stellate cells ; and it differs from that of the remaining parietal region in containing pyramidal 

 cells of larger dimensions. 



Proceeding along the postcentral gyrus from above downwards there occurs a gradual 

 diminution in the size of the large pyramidal cells, and in the number of large fibres. 



Two types of cortex can be' discriminated, one I distinguish by the name postcentral, the 

 other by the name intermediate postcentral. 



The area covered by the postcentral type of cortex is distributed over the anterior half 

 of the postcentral convolution on the convex surface of the hemisphere, and, like the precentral 

 field, it crosses the margin to coat a small area situated on the hinder part of the para- 

 central lobule. 



I have called the narrow zone of cortex which forms a posterior buffer to the postcentral 

 area proper " intermediate postcentral " because it bears some structural resemblance to the 

 first and more important field, but it differs, inasmuch as the very large nerve fibres and 

 the specially large pyramidal cells are wanting. 



In reference to function, not once in the experience of Professors Sherrington and 

 Grunbaum were movements obtained by excitation of the normal anthropoid postcentral gyrus 

 with unipolar faradisation, nor was experimental ablation of portions of the same convolution 

 attended by any positive interference with motion ; and as the same results were obtained in 

 the case of lower members of the ape family the postcentral gyrus is ousted from the position 

 it formerly held as part of the motor area. 



To establish the existence of an analogous physiological condition in the human brain 



a few excitation experiments in the course of operations on the brain will be alone necessary, 



and I am led to believe that confirmatory observations of the kind desired will shortly be 

 published. 



As to the grounds for assuming that the cortex of the posteentral gyrus constitutes 

 a terminus for the reception of common sensory impressions, it seems to have been definitely 

 proved that the tract of fibres known as von Monakow's " cortical lemniscus " is the cerebral 

 continuation of the main system of sensory neurones ; and from comparative studies in secondary 

 degeneration it has been surmised that this tract proceeds to the parietal lobe (Tschermak 

 and von Monakow), and particularly to the postcentral gyrus (Tschermak). From anatomical 

 studies in the human brain this distribution has received partial confirmation (Tschermak). 

 Further, from Professor and Madame Vogt's developmental studies it would appear that the 

 sensory fibres which medullate first proceed almost exclusively to the postcentral gyrus. A study 

 of the degeneration (retrograde) resulting from limited lesions in the postcentral gyrus, either 

 in the human being or lower animals, might provide the further information we require on 

 this point. 



From an investigation of the changes occurring as a result of old-standing, restricted lesions 

 in the internal capsule I have proved that serious alterations occur not only in the motor 

 area, but also in the postcentral gyrus. The changes in the latter gyrus consist of a whole- 

 sale destruction of large medullated fibres in the cortex on the Rolandic side, and of almost 

 all the large pyramidal cells in the same cortex. These are alterations resulting from a 

 combined destruction of sensory and motor tracts. Looking round for a disease which might 



