INTEUNAL STEUCTUKB OF THE COED 



401 



of the limbs and trunk, thus bringing all parts of the body 

 in communication with the cord. They are also connected 

 on each side of the cord with the system of nerve centers 

 called the sympatJietic 

 ganglia. (See Fig. 189.) 

 Internal structure of 

 the cord. — If we sec- 

 tion a portion of the 

 cord in such a manner 

 as to split a pair of 

 spinal nerves (see Fig. 

 188), we can make 

 out the following de- 

 tails: Like the brain, 

 the cord is seen to 

 consist of white and 

 gray matter with this 

 difference, that, in the 

 cord, the white matter 

 is on the outside. The 

 inner gray matter is in 

 the form of a letter H. 

 Two horns of this H 

 project forward (the 

 anterior cornua) and 

 two backward (the pos- 

 terior cornua). The cen- 

 tral part, correspond- 

 ing to the cross bar of the H, shows a small cavity in its 

 center which is the continuation of the ventricle cavities 

 of the brain. From the posterior and anterior cornua 

 emerge nerve fibers which unite to form the roots of the 



Fig. 189 — Roots of a dorsal spinal nerve and its 

 union with the sympathetic system; c, c, anterior 

 tissureof cord; a, anterior root;^;, posterior root 

 with spinal ganglion; s, sympathetic, and e, its 

 douhle connections with spinal nerve a' by a 

 white and a gray filament. 



EDDY. PHYS.- 



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