336 DISSECTION OF THE EABBIT 



about half an inch, giving branches to some of 

 the muscles of the neck. It then crosses the 

 carotid, about the level of the lower border of the 

 thyroid cartilage, and runs back on the sterno- 

 thyroid muscle, to which as well as to the stierno- 

 hyoid it sends branches. 

 The descendens noni is readily found crossing the carotid 

 about the point immed above, and sjwuld then be traced back- 

 wards along the sterno-thyroid muscle, and forwa/rds to the 

 point at which it leaves the main stem of the hypoglossal. 



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

 is a stout nerve which leaves the skull by the foramen 

 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 carotid artery. Follow it along the neck to the 

 thorax, and forwards 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 and to the crico- 

 thyroid muscle. 

 The sole difficulty in dissecting the superior laryngeal 

 nerve lies 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 artery, and the superior laryngeal dorsal to it. 



i. The depressor nerve is a very slender branch of 

 the superior laryngeal nerve, which runs back- 



