436 



THE CENTRAL NERVOUS SYSTEM. 



subject (Weigert, Mallory, Benda, Krause, Hardesty, Huber). In 

 figure 350 are shown two neuroglia cells from a cross-section of a 

 human spinal cord, in which the relation of neuroglia fibers to neu- 

 roglia cells is shown. 



Fig. 350. Typical neuroglia cells, from cross-section of the white matter of the 

 human spinal cord, stained after Benda' s selective neuroglia tissue staining method; 

 X 1 200 (Huber, "Studies on Neuroglia Tissue," Vaughan Festschrift, 1903). 



L THE MEMBRANES OF THE CENTRAL 

 NERVOUS SYSTEM. 



The membranes of the central nervous system (meninges) are 

 three in number: the outer,' or dura mater ; the middle, or arach- 

 noid; and the inner, or pia mater. 



Around the brain the dura mater is very intimately connected 

 with the periosteum and presents a smooth inner surface. It con- 

 sists of an inner and an outer layer, the two being separated from 

 each other only in certain regions. At such points either the inner 

 layer is pushed inward to form a duplicature, as in the falx cerebri 

 and falx cerebelli, tentorium, and diaphragma sellae, or the outer 

 layer is pushed outward to form small, blindly ending sacs. The 

 venous and lymphatic sinuses lie between the two layers. The outer 



