NERVES OF THE NECK. 373 



carotids. It then runs forwards and inwards, 

 parallel to the posterior cornu of the hyoid, to the 

 base of the tongue, in the muscles of which it ends. 



The hypoglossal nerve is readily found just outside the 

 posterior cornu of the hyoid ; it should be followed from this 

 point backwards to the skull, and forwards to the tongue. 



The ramus descendens is a branch of the hypoglossal, which 

 arises from the main nerve just before it reaches the 

 internal carotid artery. It runs backwards along the 

 outer side of the carotid for about half an inch. It then 

 crosses the carotid, about the level of the hinder border 

 of the thyroid cartilage, and runs backwards, ending in 

 muscles of the hyoid and thyroid regions. It receives 

 fibres from the first and second spinal nerves. 



The ramus descendens is easily found crossing the carotid 

 about the point named above, and should be traced backwards 

 along the sterno-thyroid muscle, and forwards 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 fora- 

 men lacerum posterius, presenting a very distinct 

 ganglionic swelling near its origin. It runs down- 

 wards 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 the following : 



Find the pneumogastric nerve in the neck, along the outer 

 side of the carotid artery. Follow it backwards along the neck 

 to the thorax, and forwards to the skull. 



a. The anterior laryngeal nerve is a small nerve, arising from 

 the pneumogastric opposite the upper border of the 

 thyroid cartilage. It rims almost directly inwards, pass- 

 ing dorsal to the carotid artery, and ends in branches 

 distributed to the mucous membrane of the larynx, and 

 to the crico-thyroid muscle. 



