THE NERVOUS SYSTEM OF MAN. 



35 



Interior Structure. — So much may be seen without 

 cutting, but on making section we find at once in all 

 parts the two kinds of nerve matter already spoken of 

 (page 19), viz., the gray granular and the white fibrous; 

 but the relative positions of these two kinds are different 

 in the different parts. In the two largest parts, viz., the 

 cerebrum and cerebellum, the gray matter is on the out- 

 side and the white fibrous matter on the inside. In these 

 the surface gray matter follows all the inequalities of 

 the surface convolutions — in fact, it is evident that the 

 convolutions are a device to increase the quantity of 

 gray matter. In the case of the cerebellum the com- 



Fig. 19. — Section of cerebellum showing arbor vitae. 



plexity of the infoldings of the surface gray matter is so 

 great as to give rise on section to the peculiar appear- 

 ance called arbor vita (Fig. 19). 



In all the other parts mentioned, viz., the medulla, 

 the optic lobes, and the thalamus, the gray matter is in 

 the center and the white matter on the outside. 



Microscopic Structure.— As already explained 

 (pages 19 and 27), the gray matter consists of cells of 

 various sizes and shapes, giving out fibers, some connect- 

 ing with other cells, and some going to form the -white 



