30 Precentral or Motor Area [CHAP. 



brain the method of Nissl shows only a few small cells, and although Ramon y Cajal and 

 others have described several varieties in their silver preparations, we do not know what 

 phj'siological importance is to be attached to them. 



Layer of Small Pyramidal Cells. 



This is another layer which for us possesses minor interest ; its component cells are not 

 so numerous as they are in some other parts of the brain, and the layer they form is neither 

 deep nor sharply differentiated from the subjacent one. 



Layer of Medium-Sized Pyramidal Cells. 



Although forming a lamina of considerable depth, these cells do not differ markedly from 

 those of the corresponding layer in most other parts of the brain, and they follow the usual 

 rule in growing larger as the cortex is descended. In the depths of the layer small stellate 

 cells are dotted about. 



External Layer of Large Pyramidal Cells. 



The line of demarcation between this and the last layer is not a shaqj one. In shape 

 the cells are distinctly pyramidal or pyriform, and they range in size from 15 to 20 by 25 

 to 30 /j, : in the cell-substance chromophilic particles are certainly distinguishable, but these 

 are by no means so obvious as in the giant cells to be described hereafter ; the nucleus is 

 large in proportion to the cell body ; even in Nissl specimens a long apical and several basal 

 processes can be distinguished, and, according to S. Ramc'm y Cajal, the shaft may be seen 

 in silver preparations to reach the surface, while the thick and numerous basal dendrites form 

 a dense and striking plexus ; Ramdn y Cajal furthermore states that in general shape these 

 cells resemble the cells of Betz, but this comparison is somewhat far-fetched. 



The probable importance of these cells in the " precentral " area cannot be denied ; at the 

 same time, from the histological standpoint, they do not constitute a distinctive feature, for 

 a layer, similar in almost every respect, may be seen over the extensive area, which I shall 

 describe later as the " intermediate precentral." 



The Layer of Stellate Cells. 



It is an important distinguishing feature of the " precentral " cortex that the layer of 

 small stellate cells, which we see so constantly and so well-represented in most other cortical 

 regions, is of such rudimentary constitution that it almost defies definition. All we can say 

 in regard to the layer is that it is just recognisable, and that minute elements of stellate 

 or pyramidal form, apparently pertaining to it, may be seen sparsely scattered among the 

 immediately adjacent external and internal large pyramidal cells. 



Layer of Giant Cells. 



It is these cells, known as the giant cells of Betz or ganglionic cells of Bevan Lewis, or, 

 as the latter observer would prefer to call them, " motor cells," which absolutely stamp this 

 type of cortex and form a certain guide to the territorial demarcation of the area. 



