

CHAP. XX.] THE VAGUS NERVE. 121 



pulmonary plexus, of which there are a right and a left plexus, 

 which anastomose freely with each other, situate behind the bifurca- 

 tion of the trachea. The ramifications of this plexus follow chiefly 

 the course of the bronchial tubes, being distributed to their mucous 

 membrane and muscular fibres. * 



After giving off the pulmonary branches, the vagi nerves pass down 

 along the oesophagus, giving off branches to it, and passing through 

 the cesophageal opening of the diaphragm are distributed to the 

 stomach. The left nerve passes in front of the cardiac orifice, sends 

 some filaments over the splenic cul de sac, and follows the course 

 of the lesser curvature ; some of its branches passing in the lesser 

 omentum to the liver, whilst the rest are distributed to the coats 

 of the stomach. The right nerve passes behind the cardiac orifice, 

 and after giving several branches to the stomach, sinks into the 

 solar plexus. 



This outline of the anatomical distribution of this extensively 

 connected nerve is sufficient to show that it is devoted to muscular 

 fibres as well as to sentient surfaces, and that it must be regarded 

 as a compound nerve, sensitive as well as motor. The existence of 

 the ganglion, which involves all the fibres of the vagus nerve, in the 

 canal of the dura mater, has led to the opinion that all its proper 

 fibres are sensitive, while those branches which go to muscles are 

 derived from its large anastomosis with the spinal accessory. Whe- 

 ther this view be correct or not, it is certain that a free communi- 

 cation exists just below the basis cranii between the vagus and the 

 spinal accessory nerves. 



The branches of this nerve, which anatomy shows to be purely 

 motor, are the pharyngeal, and the inferior laryngeal, whilst the 

 cardiac, oesophageal, pulmonary, and gastric branches are doubtless 

 of a mixed character, and the superior laryngeal is purely sensitive, 

 with the exception of those of its fibres which form the external 

 laryngeal nerve. 



The distribution of the vagus nerve in the inferior mammalia cor- 

 i;esponds very closely with that in man, and so far confirms the 

 views of function suggested by human anatomy. Its connexion 

 with the sympathetic in some of the mammalia (the dog and cat 

 for instance) is more intimate than in man, for the upper part of the 

 cervical portion of the sympathetic is closely connected with it, so 

 that they appear to form but one nervous trunk. The general dis- 

 position of the nerve in birds and reptiles does not materially differ 

 from that in man, and it has an analogous arrangement in fishes. 



The results of the numerous experiments of which this nerve has 



