THE NERVOUS SYSTEM 



287 



shallow dorsal fissure there extends a narrow septum as far 

 as the dorsal gray commissure. The nervous elements of 

 the cord are bound together by stellate neuroglia cells and 

 by processes which arise from the tapering outer ends of 



Fig. 81. — Diagram of the spinal cord showing the paths taken by nervous 

 impulses. The direction of the impulses is indicated by arrows, c.c, 

 central canal ; col, collateral fibers; c.cort, cell in the cerebral cortex; 

 eg, smaller cerebral cell; d.c, cells in dorsal horn of gray matter; d.r, 

 dorsal root ; g, ganglion of dorsal root ; g.c, ganglion cell in dorsal 

 ganglion ; g.m, gray matter ; M, muscle ; m.c, cell in medulla ob- 

 longata; m.f, motor fiber; .S, skin ; s.f, sensory fiber; sp.c, spinal 

 cord; v.c, cells in ventral horn of gray matter; v.r, ventral root of 

 nerve; wjn, white matter. (After Parker and Parker.) 



the cells lining the central canal ; these processes branch 

 repeatedly, and some of them extend to the periphery of the 

 cord. 



The white matter of the cord is composed mainly of 

 meduUated fibers. Most of these run longitudinally. Iso- 

 lated ganglion cells appear, but there seems to be no regu- 

 larity in their distribution. Strands of gray matter, largely 

 ependyma fibers, radiate from the central part of the cord 

 to the outer surface. 



The cells of the gray matter give off processes by means 



