NERVES OF THE NECK 347 



wards along the sterno-thyroid muscle, and forwards to the 

 jpoint at which it lea/ues the main stem of the hypoglossal. 

 8. The pneumogastric or vagus nerve, the tenth cranial, 

 is a stout nerve which leaves the skull by the fora- 

 men lacerum posterius, presenting a very distinct 

 swelling near its origin. It runs downwards and 

 backwards until it reaches the carotid artery, and 

 then straight backwards along the neck, lying 

 immediately to the outer side of, and slightly dorsal 

 to, the carotid artery. Entering the thorax, it runs 

 alongside the oesophagus to the stomach, where it 

 ends. 



Its principal branches are described below. 

 Find the pneumogastric nerve in the neck, along the outer 

 side of the ca/rotid artery. Follow it along the neck to the- 

 thorax, and forwa/rds to the skull. 



a. The superior laryngeal nerve is a small nerve, 



arising from the pneumogastric opposite the 



upper border of the thyroid cartilage. It runs 



almost directly inwards, passing dorsal to the 



carotid artery, and ends in branches distributed 



to the mucous membrane of the larynx (p. 350), 



and to the erico-thyroid muscle. 



The sole difficulty in dissecting the superior laryngeal 



nerve Ues in the possibility of confusing it with the descendens 



noni. This is avoided if it be remembered that, while both 



nerves cross the carotid artery, the descendens noni lies ventral 



to the a/rtery, and the superior laryngeal dorsal to it. 



i. The depressor nerve is a very slender branch of 

 the superior laryngeal nerve, which runs back- 

 wards along the neck ; lying dorsal to the 

 carotid artery, and along the inner side of the 

 main stem of the pneumogastric nerve, very 

 close to the sympathetic nerve-trunk. It ends 

 in the heart. 

 Find the depressor nerve where it leaves the superior 

 laryngeal nerve, about the level of the posterior end of the- 



