294 



THE NERVOUS SYSTEM 



^ Solar Plexus 



side, lying along the whole length of the spine. They 

 are connected by white fibers with the spinal cord, with 

 one another by gray or nonmedullated fibers, and with 

 the spinal nerves by both white and gray fibers. At their 

 upper extremities, and in other situations also, the great 

 sympathetic nerve trunks come into connection with all 

 the cranial nerves except the olfactory, auditory, and 

 optic. 



The gray fibers issuing from the ganglia are usually 

 too minute to be visible to the naked eye, and they are 



much more numerous than 

 those received by the ganglia 

 from the central system. 

 Most of these gray fibers 

 seem to convey efferent im- 

 pulses to the tissues, though 

 some are afferent, carrying 

 impulses from the viscera to 

 the central system. But a 

 certain number of the fibers 

 from the main sympathetic 

 chain turn back from the 

 ganglion toward the center, 

 some to reach the membranes 

 of the spinal cord, some to 

 follow the course of the prin- 

 cipal branch of the spinal 

 nerve which is distributed to 

 the skeletal muscles and the 

 skin. Nervous connection is 

 thus established between all these various parts. In their 

 distribution the sympathetic nerves follow closely the 

 course of the blood vessels, around which they form 



L. Sympathetic 



Chain 

 R.Sympathetic 



Chain 



Fig. 137 The solar and hypo- 

 gastric sympathetic plexuses. 



