THE CEREBRAL HEMISPHERES. 



467 



inch. In the external white layer the cells are few and small, with 

 one or two processes, and scattered in an abundant finely granular 

 matrix. The pure gray layer most abounds in cells, and which 

 are also closely aggregated in a granular matrix. Some of them 

 are very small ( ^^UTJ to s^uu f an inch), appearing frequently as 

 scarcely more than nuclei ; while there are others larger, even to 

 g ^ of an inch. (Fig. 310.) Most of them have from 1 to 6 pro- 

 cesses (usually 3, 4, or 5). Finally, in the innermost yellowish-red 

 layer, the cells are less, though still very abundant, and present the 

 same characters as those of the gray substance. 



The nerve-fibres of the gray substance of the convolutions, corne 

 from the white substance of the hemispheres, and penetrate the 

 yellowish-red layer in all directions, but more especially parallel to 



Fig. 311. 



Finest nerve-tubes of the superficial white substance of the human cerebrum. Magnified 350 dia- 

 meters. (KCttiker.) 



the surface ; and consequently they cross the main fasciculi. It is 

 these horizontal fibres which produce the white streaks before men- 

 tioned; and it is in the external white streak that the fasciculi enter- 

 ing the gray substance are lost. The fibres, however, which do 

 not take a horizontal direction, proceed onwards even through the 

 pure gray layer, and into the external white layer. Here they 

 take a horizontal direction, and form several superimposed layers 



