NERVES OF THE NECK. 367 



lies ventral to the artery, and the anterior laryngeal, dorsal 



to it. 



i. The depressor nerve is a very slender branch of 

 the anterior laryngeal nerve, which runs back- 

 wards along the neck : it lies dorsal to the 

 carotid artery, and along the inner side of the 

 main stem of the pneumogastric nerve, very 

 close to the sympathetic nerye-trunk. It ends 

 in the heart. 



Find the depressor nerve where it leaves the anterior 

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

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

 dissection in the thorax is difficult. 



b. The right posterior or recurrent laryngeal nerve 



arises 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 crieo-thyroid. 



On the left side, the nerve is not given off 

 until after the pneumogastric has entered the 

 thorax. It loops round the ductrs arteriosus, 

 and then runs forwards along the neck to the 

 larynx. (See fig. 63.) 



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

 on the left side the ductus arteriosus and 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. As 

 this shifting involves the roots of the great vessels, 

 these nerves, which are originally straight, be- 

 come pulled out into loops. 



c. Branches of the pneumogastric to the heart, lungs, 



