THE NERVES. 399 



davia into the chest. Course as far as the roots of the lungs ; upon 

 the right side : behind v. anonyma and cava super., in the sulcus 

 between trachea and oesophagus downwards to a point behind the 

 roots of the lung ; upon the left : behind v. anonyma to the left of 

 arcus aorta and behind bronchus sinister. Hence it passes into 

 the cavum mediastin. postic., divided into two branches, upon the 

 right side, behind, upon the left, before, the oesophagus, through 

 the foramen oesophageum into the abdomen. Branches : 



1. Nerv. recur rens s. laryngeus inferior, arises upon the right 

 side (where it is frequently double) before the art. subclavia, upon 

 the left, before the arcus aorta, externally to the ductus Botalli, 

 at the place where the vagus passes backwards ; it bends itself 

 under the vessels, and passes upwards behind them on the outer 

 side between trachea and oesophagus, perforates m. constrictor 

 pharyngeus infer., and enters the larynx ; terminating in the m. 

 crico-arytcenoideus [and m. arytcenoidei]. It gives branches to 

 the mucous membrane [?] and to the muscles as well to the con- 

 strictors as to the dilators of the larynx ; also to the oesophagus 

 and the trachea [the muscular fibres behind] ; anastomosing with 

 n. laryngeus super, and n. sympathicus by means of some rami 

 cardiaci. It is principally a motor nerve. 



2. Rami cardiaci thoracici, are from five to six larger, and 

 several more delicate branches, which pass into the following 

 plexus, or are lost upon the external surface of the pericardium. 



Plexus cardiaci, formed of vagus and sympathicus, entwine 

 about the great vessels of the heart, and are separated at the 

 point of reflection of the pericardium into superior and in- 

 ferior, but connected with each other as well as with those of 

 the oesophagus and trachea. 



3. Rami tracheales inferiores, lie on the anterior surface, close 

 above the bifurcation of the trachea, intermingling at this point 

 with nerv. sympathicus into a 



Plexus trachealis anterior, which is connected with the internal 

 cardiac plexus, and proceeds into the plex. pulmonalis an- 

 terior, which covers the bronchi in front. 



On the posterior surface of the trachea, a plexus tr. posterior 

 also arises, from six to seven branches, which is connected with 

 the pharyngeal and cardiac plexus, and gives branches to the 

 mucous membrane of the bronchi. 



4. Plexus pulmonalis posterior, frequently arises from the 

 trunk of the vagus ; from four to six branches, upon the right 

 and left side of the lungs. The left is the larger. Both are 

 connected together with plex. trachealis, and enter the lungs with 



