NEEVES OF THE NECK 337 



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 

 thyroid cartilage, and follow it back along the neck. Its 

 dissection in the thorax is difficult. 



b. The inferior or recurrent laryngeal nerve arises, on 



the right side, from the pneumogastric nerve at 

 the posterior end of the neck. It loops round the 

 subclavian artery, and then runs forwards along 

 the neck, lying alongside the trachea, and dorsal 

 to the carotid artery, or slightly to its inner side. 

 It supplies all the muscles of the larynx, except 

 the crico-thyroid. 



On the left side, the nerve is not given off 



until after the pneumogastric has entered the 



thorax. It loops round the arch of the aorta, and 



then runs forwards along the neck to the larynx. 



Find the nerve, as it loops round the subclavian artery, or, 



on the left side, the arch of the aorta; and follow it forwards 



along the neck to the larynx. 



The curious course of the recurrent laryngeal 

 nerves is explained by the shifting backwards of 

 the heart, which occurs during development. Ae 

 this shifting involves the roots of the great vessels, 

 these nerves become pulled out into loops. 



c. Branches of the pneumogastric to the heart, lung's, 



and oesophagus. These are of small size, and 

 are given off in the thorax : the cardiac branches 

 end in a plexus, lying between the roots of the 

 aorta and pulmonary artery. 

 Turn the lungs and heart over to one side : follow the 



pneumogastric back through the thorax, alongside the ceso- 



phagus, and trace out its branches. 



