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ANATOMY. 



each side and at each articulation of the vertebrae. They are 

 named cervical, dorsal, etc., according to location in the spinal 

 column. 



The spinal nerves supply, by their superior branches, the 

 skin and muscles of the neck and spinal column. By their in- 

 ferior branches they supply the lower portion of the body and 

 limbs and furnish other branches which in part make up the two 

 great sympathetic nerve trunks. 



FIG. 17. SPINAL CORD AND BRAIN IN DIAGRAM. (M. H. It.) 



1. Cross Section of the Spinal Cord. A, Superior median fissure; B, infe- 

 rior median fissure; C, C, superior gray horns; D, D, inferior gray horns; E, 

 central canal; F, white substance. 



2. Vertical Mid-Section of Brain. A, Medulla; B, cerebellum; C, pons or 

 bridge; D, isthmus; E, cerebrum. 



THE SYMPATHETIC SYSTEM. 



This consists of two cords, one on each side of the spinal 

 column, and extending from the head to root of tail, together 

 with all the nerves which branch from these two trunks. These 

 cords are not smooth but have enlargements called ganglia at 

 intervals along their course. Each cord resembles somewhat a 

 small, rather flat and knotted rope. 



Composition. — These two trunks are composed of nerves from 

 the medulla and from the inferior branches of all the spinal 

 nerves except the coccygeal. By this arrangement of composi- 

 tion and the frequent connections of sympathetic with cerebro- 

 spinal nerves, there is constituted a very perfect union of these 

 two systems into one great nervous machine. 



Ganglia. — The knots along the two main trunks are ganglia 

 of nerve cells and fibers. One of these, the solar plexus, is really 

 composed of two large ganglia, united by a large cord and many 



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