XVI THE NERVOUS SYSTEM 299 



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 becomes in the higher vertebrates an independent cranial 

 nerve. 



The Sympathetic System. — The main trunks of the 

 sympathetic system consist of a nervous strand on either 

 side of the spinal column. Anteriorly each trunk begins 

 in the prootic ganglion, from which it extends backward 

 within the cranial cavity, leaving the skull by the jugular 

 foramen in common with the vagus. It receives a branch 

 from the jugular ganglion, which enters the first ganglionic 

 enlargement of the main trunk. Each trunk receives a 

 branch {ramus commuiiicans) from each of the spinal 

 nerves, and where the two join there is a ganglionic en- 

 largement. The eighth spinal nerve, however, is connected 

 with the sympathetic by two communicating branches, and 

 the ninth nerve by three and sometimes four. The last 

 ganglion of the sympathetic chain consists of the ninth and 

 tenth ganglia fused into one ; it receives, besides the branches 

 from the ninth spinal nerve, a single small branch from the 

 tenth. 



A part of the fibers from the sympathetic trunks enter 

 the spinal nerves by way of the communicating rami ; other 

 fibers form independent sympathetic nerves. From the an- 

 terior portion of the trunks branches are given off to the sub- 

 clavian and occipito-vertebral arteries and anterior ends of 

 the oviducts. Farther back (from third to sixth ganglion) 

 several nerves are given off which unite to form the aieliac 

 or solar plexus^ in which several ganglionic masses occur. 

 From this plexus nerves are distributed to the stomach, 

 intestine, liver, pancreas, spleen, ovaries, oviducts, and 

 kidneys. Farther back several branches anastomose to 

 form the urogenital plexus, which supplies the kidneys, 

 ovaries, oviducts, and testes. The ganglion cells of the 

 sympathetic system are often situated very far from their 



