116 THE XKKVntS StSThM AND ITS COXSKHVATK >\ 



fibers reach them from the neighboring spinal nerve-, ami 

 their postganglionic fiber- either rejoin the spinal nerves 

 to be distributed with their peripheral branches or pass 

 directly to endings in the viscera. These two chains 

 with their connections are known under the curious old 

 name of the "sympathetic system." The word used 

 never had its psychologic meaning. 



"Autonoinic" is a more inclusive term than "sympa- 

 thetic." The sympathetic system is that part of the 

 aulonomic receiving preganglionic fibers from the thoracic 

 and lumbar portions of the spinal cord. There are auto- 

 nomic pathways beginning in the brain which are not 

 reckoned in the sympathetic system, and there are others 

 at the lower end of the spinal axis which lie outside its 

 anatomic limits. \Ye shall not often have occasion to 

 refer to the sympathetic system apart from the larger 

 complex of which it is a fraction. ( langlia belonging to the 

 autonomic -ystem, but lying outside the two sympathetic 

 chains, are found in very many localities for example, 

 behind the eye, in the walls of the heart, and clustered 

 about the arteries which supply the digestive organs. 

 They are not to be confused with the ganglia connected 

 with afferent paths, which are found, for the most part, 

 close to the point of entrance of such paths into the central 

 nervous system. 



We may now pass to a condensed statement of tin- 

 operations of the autonomic system upon various depart - 

 incut- of the physiologic mechanism. We may well speak 

 first of its control of the circulation. This is exerci-ed 

 partly through the cardiac and partly through the vaso- 

 motor nerves. The heart is a muscular pump, and on the 

 force and frequency of its beat depends the volume of 

 blood sent through the arterie- to all regions of the body. 

 Its beating is fundamentally automatic, but subject to 

 exten-ive regulation through the nerve-centers. Auto- 

 nomic paths to the heart-muscle can be traced from two 

 sources. ( )f these, the most conspicuous and the earliest 

 to be .-tudied is represented by certain libers in the large 



