THE SYMPATHETIC NERVOUS SYSTEM 225 



ganglia of the sympathetic nervous system which are distributed 

 widely throughout the body, and partly from the central nervous 

 system. The nervous impulses involved in the second type of 

 control are, moreover, always distributed to the viscera through 

 the sympathetic system. 



A clear analytic description of the visceral nervous systems is 

 extremely difficult, and there is wide diversity of usage, not only 

 in the terminology employed in these descriptions, but also in 

 the fundamental concepts upon which they are based. The 

 brain and spinal cord and the cranial and spinal nerves and their 

 end-organs in the aggregate constitute the cerebro-spinal nervous 

 system. The cell bodies of the neurons of this system all lie 

 within the spinal cord and brain (including the retina) or in the 

 ganglia on the sensory roots of the cranial and spinal nerves. 

 There are, however, innumerable other ganglia distributed very 

 widely throughout the body, which are connected with each 

 other and with the central nervous system by intricate nervous 

 plexuses. These constitute the sympathetic ganglia and nerves, 

 or in the aggregate the sympathetic nervous system. 



There is an especially important group of sympathetic ganglia 

 which are arranged in two longitudinal series extending one on 

 each side of the vertebral column. These ganglia constitute the 

 vertebral sympathetic trunks or chains, and throughout the 

 middle part of the body there is one ganglion of each trunk for 

 each spinal root (Fig. 41, p. 107). Communicating branches con- 

 nect the ganglia of the trunks with their respective spinal roots, 

 and from these ganglia sympathetic nerves extend out periph- 

 erally to ramify among the viscera and other tissues of the 

 body. Ganglion cells are scattered among these peripheral 

 sympathetic nerves, and in some places, especially among the 

 abdominal viscera, these cells are crowded together to form large 

 ganglionic plexuses (Fig. 108). 



When further analyzed, the sympathetic nervous system is 

 found to consist of two imperfectly separable parts. The first 

 is a diffusely arranged peripheral plexus of nerve-cells and fibers 

 adapted for the local control of the organs with which it is con- 

 nected. This we shall call the peripheral autonomous part of the 

 sympathetic system (this is not the same as the autonomic ner- 

 vous system of Langley, see p. 229). The second part of the 



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