THE NERVOUS SYSTEM. 



•Ill 



extremely abundant, otherwise presenting tlic same charad 

 as those in the grey substance, having sometimes pale, some- 

 times pigmentary contents ; the latter in the inner Layers more 

 particularly, and in old persons. 



The nerve-fibres of the grey substance of the convolutions, 

 arise, as it is easy to demonstrate, from the medullary substance 



Fig. 149. 



of the hemispheres, 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 especially parallel to the 

 surface, and consequently crossing the main fasciculi. 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 grey substance, are 

 lost. In fact, as these proceed more outwardly, they con- 

 stantly decrease in size, owing to their giving off lateral fibres, 

 and to the attenuation and separation of their elements, until, 

 when they have reached the grey layer, they become lost to 

 sight, although if more closely traced they may still be 



Fig. 149. From the internal portions of the grey layer of the convolutions of the 

 human cerebrum, x 350 diam. Nerve-cells; a, larger; b, smaller; c, nerve-fibres 

 with axis-cylinder. 



