186 



NERVE-CENTRES 



[CH. XYI. 



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. 180, 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 envelop- 

 ing other nerve-cells ; the col- 

 laterals also terminate in a 

 similar way. The longest type 

 of axis cylinder is that which 



FIG. 181. Pyramidal cell of human cerebral cortex. 

 Golgi's method. 



passes away from the nerve-centre, 

 and gets bound up with other 

 similarly sheathed axis cylinders 

 to form a nerve; but all ulti- 

 mately terminate in an arbor- 

 escence of fibrils in various 

 end - organs (end-plates, muscle 

 spindles, etc.). 



H 



FIG. 182. Cerebral cortex of mammal, prepared 

 by Golgi's method. A, B, C, D, F, nerve- 

 cells; E, neuroglia-cell. (Ramon y Cajal.) 



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

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



