832 



HITCHCOCK'S ANATOMY 



the body. A ganglion is found upon the posterior root, just 

 before it unites with the anterior. 



597. Origin of the Spinal Nerve s— Between each of 

 the vertebrse the spinal nerves are givenofF. These are made 

 up of fasciculi, and each fasciculus of distinct fibers which 

 somewhat resemble muscular fiber. They arise on each side 

 of the cord by two roots, one given off from the anterior and 

 the other from the posterior part of the lateral cords ; the 

 anterior root being the one that is designed to produce mo- 

 tion, and the posterior giving sensation to the parts on which 

 it is distributed. These two roots unite as soon as they have 

 fairly left the spinal cord, after which they proceed as a single 

 nerve. (See Fig. 318.) 



598. Groups of Spinal Nerves —These 

 nerves are grouped together, and have 

 the same name as the groups of verte- 

 brae in which they are located. 



Fig. 319. 



8 Cervical. 

 12 Dorsal. 



5 Lumbar. 



6 Sacral. 



The last nine are additional, or supple- 

 mentary to the spinal cord, and not prop- 

 erly a portion of it. They are called 

 the cauda equina. 



599. Plexuses —Most of these nerves 

 are grouped together soon after leaving 

 the spinal column, each group being 

 called a plexus (from the Greek " to 

 weave 7 '), which is simply a net-w T ork of 

 nervous fibers. Although there is to the naked eye a com- 

 plete interlacement and an apparent loss of fiber, yet by the 

 microscope these fibers can be distinctly traced through the 

 whole mass, w T ith the exception of a few which are inter- 

 changed for purposes to be described hereafter. After emerg- 



Diagram to show the De- 

 cussation (crossing from 

 side lo side) of Nerve Fi- 

 bers in a Nerve. 



517. Give the origin of the spinal nerves. 59S. State the groups of the spinal nerves. 

 599. Describe the nature of the plexuses. 



