NERVOUS SYSTEM. 343 



The recurrent n rrve ofthe left side originates from the par 

 vaguni, by the side of the anterior aorta, and coils round the root 

 of the posterior aorta, including that vessel in a sling as it were ; 

 but, on the right side, it leaves the trunk as the latter passes the 

 first rib, winding forward within the angle formed between the 

 anterior aorta and its first large branch — the posterior cervical 

 artery. The recurrent nerve (so denominated from its retrograde 

 course) then takes the first part of its reflected passage, situated 

 above and outwardly to the par vagum ; by degrees, however, in 

 running up the neck, it approaches the trunk, gains the inner side 

 of it, and along the anterior half of the neck is found concealed 

 between the carotid artery and the trachea. Having reached the 

 top ofthe air-tube, it spreads into many fine terminating branches, 

 several of which run to the muscles of the larynx, though the 

 principal of them creep along the sides of the thyroid cartilage, 

 and end in ramifications upon the membrane of the glottis. Its 

 branches are — 1. Twigs to the pulmonary plexus ; and, on the 

 left side, some also to the cardiac plexus. 2. Twigs to the 

 posterior cervical ganglion.- 3. Long slender ramifications both 

 to the esophagus and trachea, in its passage up the neck. 



The pulmonary plexuses, inferior and superior, consist of 

 networks of nervous filaments, some of which are of large size, 

 surrounding the great vessels constituting the roots ofthe lungs. 

 They are composed of branches and threads of nerves from the 

 par vagum and recurrent of one side, and of similar ramifications 

 from the opposite side : the inferior plexus clings to the trachea 

 at its division, and spreads under the bronchial tubes and pul- 

 monary vessels ; the superior, which receives several reflected 

 branches from the par vagum, lies behind the roots of the lungs, 

 and is less considerable than the inferior. From these plexuses 

 the numerous nervous filaments are derived which cling to 

 the bronchial ramifications and pulmonary vessels, for the sup- 

 ply of the parenchymatous and vascular structures, and lining 

 membrane of the lungs. Moreover, the par vagum, in the chest, 

 detaches many twigs to the esophagus, which interlace its mus- 

 cular coat by uniting with others from the opposite nerve : in 

 this manner another plexus is produced, which is named the 

 esophageal. 



The par vagum having entered the abdomen, clinging to the 

 sides of the esophagus, the nerve on one side is differently dis- 

 tributed to that on the other. They both run to the stomach ; 

 but the left nerve, prior to reaching it, divides into two sets of 

 branches. One of these pursue their course backward, and 

 spread over the upper part of the organ, sending some twigs 



