THE VAGUS NERVE 423 



might be of sympathetic origin. The present paper presents the 

 results of some experiments performed on dogs to determine 

 by degeneration methods to what extent sjniipathetic fibers 

 entered into the composition of the vagus. 



Figure 1 is a diagram of the right ^'agus nerve in the dog, 

 showing the relations with the sympathetic, and the origin of 

 the branches. Note that the two trunks are closely united 

 from high in the neck to the upyier thoracic region. Note also 

 that just below the bronchial rami, r.b., each \-agus gives off a 

 branch which goes to unite with the nerve of the opposite side. 

 In addition each nerve is also joined by smaller twigs from the 

 contra-lateral vagus. Sections of either vagus below the level 

 of the bronchial rami may include fibers which originate in 

 the opposite vagus, a fact of importance in interpreting the 

 histolog>^ of the degenerated nerves. 



It would be possible for post-ganglionic libers to enter the vagus 

 from communications with the superior cervical ganglion of 

 the sympathetic. In the ])re]iaration of the former paper (Chase 

 and Ranson) we were unable, in a study of serial sections, to 

 trace any considerable mnnber of such fibers into the vagus. 

 Throughout their course in the neck, although the two ner\-es 

 are contained in a conunon sheath, no interchange of fibers 

 could be traced. At the level of tlic inferior cervical (g.c.i.) 

 ganglion of the sympathetic, however, the association of the 

 vagus and sympathetic is veiy close, and numerous large bun- 

 dles of sympathetic unmyelinated fibers can be seen in serial 

 sections entering and leaving the vagus tiimk. If, then, any 

 considerable proportion of the unmyelinated fibers in the thoracic 

 \'agus of the dog have their origin in the s^^upathetic trunk, 

 they nuist arise from cells in the inferior cervical ganglion g.c.i., 

 or ganglion stellatum, g.s. 



METHODS 



The right vagus ner\'e was se\-ered in a number of dogs. In 

 some cases it was separated from the sympathetic tnmk high 

 in the neck and about an inch of the vagus nerve was removed 

 (fig. 1, A). There would then be no interference with fibers 



THE JOLKXAL OF COMTAR-VTIVE XEUROLOGV, VOL. 26, XO. 4 



