194 



NERVE-CENTRES. 



[CH. XVII. 



In preparations made by Golgi's chromate of silver method, the 

 cells and their processes are stained an intense black by a deposit 

 of silver. The various structures in the cells (nucleus, granules, 

 fibrils, etc.), are not visible in such preparations, but the great 

 advantage of the method is that it enables one to follow the 

 branches to their finest ramifications. It is thus found that the 

 axis cylinder process is not unbranched as represented in fig. 200, 

 but invariably gives off side-branches, which are called collaterals ; 

 these pass into the adjacent nerve tissue. The axis cylinder 

 then acquires the sheaths, and thus is converted into a nerve-fibre. 

 This nerve-fibre sometimes, as in the nerve-centres after a more 

 or less extended course, breaks up into a terminal arborescence 

 enveloping other nerve-cells ; the collaterals also terminate in a 



Fig. 200. Multipolar nerve-cell from anterior horn of spinal cord ; a, axis cylinder 

 process. (Max Schultze.) 



similar way. The longest type of axis cylinder is that which 

 passes away from the nerve-centre, and gets bound up with 

 other similarly sheathed axis cylinders to form a nerve ; but 

 all ultimately terminate in an arborescence of fibrils in various 

 end organs (end-plates, muscle spindles, etc.). 



In the grey matter of the cerebrum the nerve-cells are various 

 in shape and size, but the most characteristic cells are large and 

 pyramidal in shape. They are especially large and numerous in 

 what are called the motor areas of the brain. The apex of the 

 cell is directed to the surface; the apical process is long and 

 tapering, and finally breaks up into fibrils that lie parallel to the 

 surface of the brain (tangential fibres). From the lower angles 

 and other parts branching processes originate ; the axis cylinder 

 comes off from the base of the pyramid. The next figure (fig. 201) 

 shows the typical appearance of one of these cells, showing the 

 various points just described. The following figure shows a section 



