THE PNEUMOGASTEIC NERVE. 561 



inwards to the laiynx beneath the internal carotid artery, and divides 

 beneath that vessel into two branches, distinguished as external and in- 

 ternal laryngeal, both of -which ramify in the structures of the larynx. 



The external laryngeal branch, the smaller of the two divisions, o-ives 

 backwards, at the side of the pharynx, filaments to the pharyngeal 

 plexus and the lower constrictor muscle ; and it is finally prolono-ed be- 

 neath the muscles on the side of the larynx to the crico-thyroid muscle 

 in which it euds. In the neck this branch joins the upper cardiac 

 nerve of the sympathetic. 



The internal laryngeal branch is continued to the interval between the 

 hyoid bone and the thyroid cartilage, where it perforates the thyro-hyoid 

 membrane with the laryngeal branch of the superior thyroid artery, and 

 distributes filaments to the mucous membrane : some of these are di- 

 rected upwards in the aryteno-epiglottidean fold of mucous membrane 

 to the base of the tongue, the epiglottis, and the cpiglottidean glands ; 

 while others are reflected downwards in the lining membrane of the 

 larynx, extending to the corda vocalis, on the inner side of the laryngeal 

 pouch. A slender communicating branch to the recurrent laryngeal 

 nerve descends beneath the lateral part of the thyroid cartilage. A 

 branch enters the arytenoid muscle, some filaments of which seem to 

 end in the muscle, while others proceed through it to the mucous 

 membrane. 



Recurrent laryngeal branch. — The recurrent or inferior laryngeal 

 branch of the vagus nerve, as the name expresses, has a reflex course to 

 the larynx. 



The nerve on the riyM side arises at the top of the thorax, winds 

 round the subclavian artery, and passes beneath the common carotid 

 and inferior thyroid arteries in its course towards the trachea. On the 

 left side the recurrent nerve is bent round, below and behind the arch 

 of the aorta, immediately beyond the point where the obliterated ductus 

 arteriosus is connected with the arch, and is thence continued upwards 

 to the trachea. 



Each nerve in its course to the larynx is placed between the trachea 

 and oesophagus, supplying branches to both tubes ; and each, while making 

 its turn round the artery, gives nerves to the deep cardiac plexus. At 

 the lower part of the cricoid cartilage the recurrent nerve distributes 

 branches to supply all the special muscles of the larynx, except the crico- 

 thyroid muscle, which is supplied from the upper laryngeal nerve. It 

 likewise gives a few offsets to the mucous membrane, and a single com- 

 municating filament which joins the long branch of the upper laryngeal 

 nerve beneath the side of the thyroid cartilage. 



Cardiac branches. — Branches to the heart are given off by the 

 pneumo-gastric nerve both in the neck and in the thorax. 



The cervical cardiac branches arise at both the upper and the lower 

 part of the neck. The vpiJer branches are small, and join the cardiac 

 nerves of the sympathetic. The loiver, a single branch, arises as the 

 pneumo-gastric nerve is about to enter the chest. On the right side 

 this branch lies by the side of the innominate artery, and joins one of 

 the cardiac nerves destined for the deep cardiac plexus ; it gives some 

 filaments to the coats of the aorta. The branch of the left side 

 crosses the arch of the aorta, and ends in the superficial cardiac plexus. 



The thoracic cardiac branches of the right side leave the trunk of the 

 pneumo-gastric as this nerve lies by the side of the trachea, and some 



VOL. I. 



