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INTRODUCTION TO NEUROLOGY 



the bodies of the pyramidal cells (Fig. 126). Still others twine 

 around the dendrites for their entire length. The dendrites of 

 the pyramidal cells are very rough and thorny, and these thorns 

 are supposed by some to be the points where the actual synaptic 

 connections are effected. 



Besides the lamination caused by the bands of tangential 

 nerve-fibers already referred to, the cell bodies themselves are 

 arranged in layers whose pattern varies in different parts of the 



Fig. 126. Section of the human cerebral cortex from the precentral 

 gyrus, illustrating the details of the terminal arborizations of the incoming 

 fibers (a) in the form of a closely woven feltwork of fibers (b, c, d) around the 

 cell bodies of the large pyramidal cells of the cortex. The cells themselves 

 are not stained in the preparation, but their outlines are clearly indicated 

 by the pericellular basket-work by which they are enveloped. (After 

 Ilam6n y Cajal.) 



cortex. Neurologists enumerate these layers differently. Brod- 

 mann, who has studied this question very exhaustively, enumer- 

 ates six primary layers which in most parts of the cortex are 

 arranged essentially as shown in the accompanying diagram 

 (Fig. 127). The six layers here recognized are present in most 

 but not in all parts of the cortex. In the different regions one or 

 more of these layers may be reduced, enlarged, or subdivided; 

 and on the basis of these differences the entire cortex has been 



