iv J Poxtn'ittntl- or Scusonj Area 73 



down tlu> post cent nil gyms, representing in earh tlie number of (.'ells present in the respective 

 layers in a transverse millimetre f substance, the result being that for every one cell seen 

 in the internal layer, close on three can be found in the external, and this preponderance 

 is maintained with slight variations throughout the whole extent of the gyrus. In size and 

 general appearance, these cells resemble the common type of suprastellate, large pyramidal 

 cell, and accordingly do not call tor special description. 



But just as cells of a special character are interspersed among the external large pyramidal 

 cells, so it is again with this lamina. Now the cells to which I refer are in all probability the 

 elements which Betz and others have seen and regarded as identical with the giant cells of the 

 precentral area, and as I am convinced of the incorrectness of this assumption, it is important 

 that I should describe their characters in detail. 



First, as regards size, it is perfectly true that they are considerably larger than any 

 other cells in the postcentral region, but, as may be observed in figure 6, when they are 

 drawn under a high power and represented beside precentral Betz cells, drawn at the same 

 magnification, the difference between the two becomes very obvious ; indeed the diameters 

 of the largest postcentral cell, which may be put down as 20 x 50 /j,, fall well below the 

 diameters of even an average-sized precentral giant cell. 



There are also differences in sectional outline. In describing the conformation of the 

 precentral giant cell it was soon decided that the term pyriform was the most applicable, 

 here after looking very carefully at a number of these postcentral cells I have come to the 

 conclusion that the expression pyramidal is the best. I have also noticed that the apical 

 extension tapers away very gradually, and the point where it joins the body proper, not 

 being marked by any more or less sudden attenuation, as it is in the case of the precentral 

 cell, is difficult to determine. 



Another reason why these cells stand out prominently is that they are richly supplied 

 with chromophilic elements; in this respect they resemble the precentral giants. For the same 

 reason the outline of the nucleus is obscured, and in consequence this structure looks small. 



Unlike the typical cells of Betz these elements are not found lying in nests or clusters, 

 but prefer the solitary arrangement. 



Concerning distribution, these cells are practically confined to the paracentral extension 

 and the upper sixth of the lateral portion of the postcentral gyrus, and they are undoubtedly 

 seen at their best, both as regards number and magnitude, in the first-mentioned situation; 

 crossing on to the lateral surface of the hemisphere they suffer a reduction in size, at the 

 same time becoming scarcer; then, when the upper sixth of the gyrus is passed, they rapidly 

 give way to much smaller chromophilic elements, not unlike those already noted as constituents 

 of the external layer of large pyramidal cells, and they finally disappear altogether before 

 the lower extremity of the convolution is reached. 



In conjunction with the tact that these large cells occur in a part where the remainder 

 of the lamination is essentially of a postcentral t} r pe, it is to be observed that they occupy 

 that particular cortex, wherein the plexus of coarse medullated postcentral nerve fibres is 

 richest. And, in addition to normal histological differences, their behaviour in certain patho- 

 logical conditions leaves no doubt that we have previously been in error in including them 

 in the category of motor cells, because when we discuss their function, I shall point out 

 that they are not included in the giant cell destruction seen in cases of amyotrophic lateral 



C. 10 



