THE SYMPATHETIC NERVOUS SYSTEM 



335 



and in the thoracic and abdominal cavities. It must not be too sharply de- 

 limitated from the cerebrospinal nervous system, since it contains great numbers 

 of fibers which run to and from the brain and spinal cord. For example, the 

 vagus nerve contains many fibers which are distributed through the thoracic 

 and abominal sympathetic plexuses for the innervation of the viscera. In the 

 same way the spinal nerves are connected by communicating branches or rami 

 communicates with the sympathetic trunks. 



The sympathetic trunks are two nerve cords which extend vertically through 

 the neck, thorax, and abdomen, one on each side of the vertebral column (Fig. 

 248). Each trunk is composed of a series of ganglia arranged in linear order 

 and bound together by short nerve strands. Every spinal nerve is connected 

 with the sympathetic trunk of its own side by one or more gray rami commu- 

 nicantes through which it receives fibers from the sympathetic trunk. Fibers 

 reach this trunk from the thoracic and upper lumbar nerves by way of the white 

 rami communicantes (Fig. 257). The sympathetic trunk also gives off branches 

 which enter into the formation of the nerve plexuses which are associated with 

 the larger arteries. The largest of these plexuses is the celiac, which is associ- 

 -ated with the upper portion of the abdominal aorta and its branches. In this 

 plexus and located in close relation to the abdominal aorta are the celiac, 

 mesenteric, and aorticorenal ganglia, all of which are in man grouped hi a pair 

 of large irregular masses designated as the celiac ganglia and placed one on 

 either side of the celiac artery (Fig. 257). The sympathetic ganglia may be 

 grouped into three series as follows: (1) the ganglia of the sympathetic trunk, 

 arranged in linear order along each side of the vertebral column and joined 

 together by short nerve strands to form the two sympathetic trunks; (2) col- 

 lateral ganglia, arranged about the aorta and including the celiac and mesenteric 

 ganglia; and (3) terminal ganglia, located close to or within the structures 

 which they innervate. As examples of the latter group there may be men- 

 tioned the ciliary and cardiac ganglia and the small groups of nerve-cells in 

 the myenteric and submucous plexuses (Fig. 257). 



FUNDAMENTAL FACTS CONCERNING VISCERAL INNERVATION 



General visceral afferent fibers are found in the ninth and tenth cranial 

 nerves and in many of the spinal nerves, especially in those associated with the 

 white rami (thoracic and upper lumbar nerves) and in the second, third, and 

 fourth sacral nerves. These afferent fibers take origin from cells in the cerebro- 

 spinal ganglia (Fig. 249). From these ganglia the fibers run through the corres- 



