THE NERVOUS SYSTEM. 



387 



others of larger dimensions, up to 0*016 and 0-02 of a line (Fig. 149). 

 Their figure is pyriform or fusiform, tri- or multangular, also perhaps 

 more rounded, by far the greater number having from one to six pro- 

 cesses, usually three, four, or five ; and where this is not the case, they 

 may have been torn off in the preparation, since stumps of them may 

 be very readily noticed in the cells, which are altogether very delicate. 

 In the innermost yellowish-red layer, lastly, the cells are again rather 

 more scanty, though still extremely abundant, otherwise presenting the 

 same characters as those in the gray substance, having sometimes pale, 

 sometimes pigmentary contents ; the latter in the inner layers more 

 particularly, and in old persons. 



The nerve-fibres of the gray substance of the convolutions, arise, as it 

 is easy to demonstrate, from the medullary substance of the hemispheres, 



Fig. 149. 



and penetrate, bundle after bundle, directly, and all parallel, into the 

 yellowish-red layer. Arrived here, many fibres separate from the rest, 

 and penetrate the yellowish-red layer in all directions, but more espe- 

 cially parallel to the surface, and consequently crossing the main fasci- 

 culi. When these horizontal fibres are more closely aggregated, they 

 produce the above-described whiter or clearer streaks in this layer, the 

 outer of which streaks is situated exactly at the point, where the fasciculi 

 which enter the gray substance, are lost. In fact, as these proceed more 

 outwardly, they constantly decrease in size, owing to their giving off lateral 



FIG. 149. From the internal portions of the gray layer of the convolutions of the human 

 cerebrum, magnified 350 diameters. Nerve-cells : a, larger; 6, smaller ; c, nerve-fibres with 

 axis-cylinder. . 



