VAGUS NERVE AND BRANCHES. 331 



mon carotid artery, arid courses over the arch of the aorta, and beneath 

 the root of the lung, forming there a larger plexus than on the right side. 

 From the pulmonic plexus one or two brandies pass to the front of the 

 oesophagus, and join with offsets of the right nerve in a plexus ; but its 

 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 in the thorax are the follow- 

 ing : 



a. The recurrent or inferior larynyeal nerve, arising on the right side 

 on a level with the subclavian artery, and on the left, at the lower border 

 of the arch of the aorta, bends backwards 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. 



b. Cardiac branches (thoracic). Besides the cardiac branches furnished 

 by the vagus in the neck, other offsets pass in front of 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 branch of each vagus 

 nerve (p. 114) may be now seen. The branch of the right lies by the 

 side of the innominate artery, and joins a cardiac nerve 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. 



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

 one on the anterior and the other on the posterior aspect of the root. 



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

 communicate with filaments of the sympathetic on the pulmonary artery : 

 these nerves are best seen on the left side. 



The posterior branches are the largest and much the most numerous. 

 Forming a plexiform arrangement (posterior pulmonary plexus) behind 

 the root of the lung by the flattening and splitting of the trunk of the 

 nerve, they are joined by filaments from the third and fourth ganglia of 

 the knotted cord of the sympathetic, and are conveyed into the lung on 

 the divisions of the air tube. 



d. (Esophayeal branches are furnished to the gullet, but in greatest 

 abundance in the lower half. Below the root of the lung the branches of 

 the pneumo-gastric nerves surround the oesophagus with a network (plexus 

 gala}. 



SYMPATHETIC NERVE. In the thorax the sympathetic nerve consists 

 of a knotted cord along each side of the spinal column, which communi- 

 cates with the spinal nerves : and of a large prevertebral or cardiac plexus, 

 which distributes branches to the heart and the lungs. 



The gangliated cord will be seen in a future stnge of the dissection after 

 the heart and the lungs have been removed. 



The CARDIAC PLEXUS lies at the base of the heart around the great 

 bloodvessels. A part of this network, the superficial cardiac plexus, has 

 been already described (p. 314). The remaining part, or the deep cardiac 

 plexus, is placed beneath the arch of the aorta. 



Dissections. The cardiac plexus has been injured by the previous ex- 

 amination of the heart, so that it should be dissected in a body in which 

 the heart and the large vessels are entire. 



Dissection. The arch of the aorta is to be cut across near the heart 



