THE PNEUMO-GASTRIC NERVE. 471 



with the phrenic artery from the aorta, and with the musculo- 

 phrenic branch of the internal mammary. 



The PNEUMO-GASTRIC or VAGUS NERVE passes through the thorax Vagus 

 to the abdomen. In the lower part of the thorax the right and left ne 

 nerves have a similar position, for they pass behind the root of the 

 lung, each on its own side, and along the oasophagus to the stomach. 

 But above the root of the lung, the two nerves have different rela- 

 tions. Each supplies branches to the viscera, viz., to the heart, the 

 windpipe and lungs, and the gullet. 



The right vagus enters the thorax between the subclavian artery Right vagus 

 and the innominate vein, and is directed obliquely backwards, 

 by the side of the trachea, to the posterior aspect of the root of the 

 lung, where it gives rise to the posterior pulmonary plexus. From and on 

 the plexus two large offsets are continued to the back of the gullet, 

 and unite below into one trunk, which reaches the posterior surface 

 of the stomach. 



The left nerve appears in the thorax on the outer side of the left Left nerve 

 common carotid artery, and courses over the arch of the aorta, and ^ iung 

 beneath the root of the lung, forming there a larger plexus than on 

 the right side. From the pulmonary plexus one or two branches and on 

 pass to the front of the oesophagus, and join with offsets of the 

 right nerve in a plexus ; but the pieces are collected finally into 

 one trunk, which is continued on the front of the gullet to the 

 anterior part of the stomach. 



The branches of the pneumo-gastric nerve seen in the thorax are Branches 

 the following : are: ~ 



a. The recurrent or inferior laryngeal nerve, arising on the right Recurrent 

 side below the subclavian artery, and on the left at the lower larvn g eal - 

 border of the arch of the aorta immediately external to the ductus 

 artenosus, bends inwards to the trachea, along which it ascends to 

 the larynx. On each side this branch is freely connected with the 

 cervical cardiac branches of the sympathetic nerve, especially on 

 the left side beneath the arch of the aorta. 



6. Cardiac branches (thoracic). Besides the cardiac branches fur- Cardiac 

 nished by the vagus in the neck, other offsets pass in front of branches : 

 the trachea to the cardiac plexus. On the right side they come 

 from the trunk of the vagus and the recurrent branch, but they 

 are supplied by the recurrent nerve alone on the left side. 



The termination of the lower cervical cardiac bi'anch of each lower cervi- 

 vagus nerve may now be seen. The branch of the right nerve branch. 1& 

 lies by the side of the innominate artery, and joins a cardiac offset 

 of the sympathetic of the same side ; and the branch of the left 

 vagus crosses over the arch of the aorta, to end in the superficial 

 cardiac plexus (p. 457). 



c. Pulmonary branches. There are two sets of nerves for the Pulmonary 

 lung, one on the anterior and the other on the posterior aspect 

 of the root. 



The anterior branches, two or three in number, are small, and small 

 communicate with filaments of the sympathetic on the pulmonary an 

 artery : these nerves are best seen 011 the left side. 



