Tin-: VAGUS -V/v 



by communications from the sympathetic and from the pharyngeal plexus, and it 

 gives a small branch tot he internal carol id artery. 



(a) The internal branch accompanies the superior larynireal artery In I he inter- 

 val between the upper border of the thvreoid cartilage and the great cornu of the 

 hyoid bone. It passes under cover of the thyreo-hyoid muscle and pierces die hyo- 

 thyreoid membrane to train the interior of the pharynx, where it lies in the outer 

 wall of the sinus piriformis and divides into a number of diverging branches. The 

 ascending branches supply the mucous membrane on both surfaces of (he epiglottis, 

 and probably t hat of a small part of the root of the tongue. The descending branches 

 ramify in t he mucous membrane lining the larynx, and supply the mucous membrane 

 which covers the back of the cricoid cartilage. One of the descending branches 

 passes downw&rdfi on the internal muscles of the larynx to anastomose with the ter- 

 minal part of the inferior (recurrent) laryngeal nerve. 



(b) The external branch runs downwards on the inferior constrictor to the lower 

 border of the thvreoid cartilage, where it ends, for the most part, in the crico-thyreoid- 

 eus. A few filaments pierce the crico-thyreoid membrane and are distributed to the 

 membrane lining the larynx. It occasionally gives off a cardiac branch which joins 

 one of the cardiac branches of the sympathetic ; it also furnishes twigs to the inferior 

 const rid or, and communicat ing twigs tot he pharyngeal plexus, and it receives a com- 

 munication from the superior cervical ganglion of the sympathetic. 



(5) The recurrent (inferior or recurrent laryngeal) nerve of the right side 

 arises at the root of the neck in front of the first stage of the right subclavian artery. 

 It hooks around the artery, passing below and then behind that vessel, and runs 

 upwards and slightly inwards, crossing obliquely behind the common carotid artery 

 (fig. 700). Having gained the side of the trachea, it runs upwards in the groove 

 between that canal and the (esophagus, accompanied by branches of the inferior 

 thvreoid artery, and, near the level of the lower border of the cricoid cartilage, be- 

 comes the inferior laryngeal nerve. In its course the recurrent nerve gives off branches 

 to the trachea, oesophageal branches to the oesophagus and pharynx, and, near its 

 commencement, one or more inferior cardiac branches. It communicates with the 

 inferior cervical sympathetic ganglion and with the superior laryngeal nerve. 



The inferior laryngeal nerve, the continuation of the recurrent, ascends between 

 the trachea and oesophagus, enters the larynx under cover of the inferior constrictor 

 of the pharynx, and divides into two branches, anterior and posterior. The anterior 

 branch passes upwards and forwards on the crico-aryta'noideus lateralis and thyreo- 

 arytspnoideus, and supplies these muscles and also the vocalis, arytsenoidcus 

 obliquus, ary-epiglotticus, and thyreo-epiglotticus. The posterior branch, passing 

 upwards, supplies t he crico-arytamoideus posterior and arytamoideus obliquus, and 

 anastomoses with the internal branch of the superior laryngeal nerve. 



On the left side the recurrent nerve arises in front of the aortic arch and winds 

 around the concavity of the arch lateral to the ligamentum arteriosum. It crosses ob- 

 liquely behind the root of the left common carotid artery, gains the angular interval 

 between the (esophagus and trachea, and corresponds with the nerve of the right 

 side in the remainder of its course and distribution (fig. 706). 



(6) Cardiac branches. Of these, there are two sets, the superior and inferior. 

 All the branches of both sets pass to the deep part of the cardiac plexus except a 

 superior branch on the left side that passes to the superficial part of the cardiac 

 plexus. 



(a) The superior (superior and inferior cervical) cardiac nerves arise from 

 the vagus and its branches in the neck (figs. 706 and 718). Some of these branches on 

 both sides join with the cardiac branches of the sympathetic in the neck and pass 

 wit h them to the cardiac plexus. Some on the right side pass independently through 

 the thorax to the deep part of the cardiac plexus, and a branch on the left side pi: 

 through the thorax to the superficial part of the cardiac plexus. 



(1>) The inferior (thoracic) cardiac branches. These branches on the right 

 side arise in part from the recurrent nerve and in part- from the main trunk of the 

 vagus, while on the left side they usually arise entirely from the recurrent. All these 

 branches pass to the deep part of the cardiac plexus (figs.7(l(> and 718). 



(7) The bronchial (pulmonary) branches are anterior and posterior (fig. 706). 

 (a) The anterior bronchial (pulmonary) branches consist of a few small 



branches which arise 1 at the upper border of the root of the lung. They pass for- 

 wards to gain the anterior aspect of the bronchus, where they communicate with the 



