THE TENTH OR PNEUMOGASTRIC NERVE. 821 



The auricular branch (Arnold's) arises from the ganglion of the root, and is 

 joined soon after its origin by a filament from the petrous ganglion of the glosso- 

 pharvngeal ; it passes outward behind the jugular vein, and enters a small canal 

 on the outer wall of the jugular fossa. Traversing the substance of the temporal 

 bone, it crosses the aqueductus Fallopii about two lines above its termination at 

 the stylo-mastoid foramen ; here it gives off an ascending branch, which joins the 

 facial : the continuation of the nerve reaches the surface by passing through the 

 auricular fissure between the mastoid process and the external auditory meatus, and 

 divides into two branches, one of which communicates with the posterior auricular 

 nerve, while the other supplies the integument at the back part of the pinna and 

 the posterior part of the external auditory meatus. 



The pharyngeal branch, the principal motor nerve of the pharynx, arises from 

 the upper part of the inferior ganglion of the pneumogastric. It consists principally 

 of filaments from the accessory portion of the spinal accessory : it passes across 

 the internal carotid artery (in front or behind) to the upper border of the Middle 

 constrictor, where it divides into numerous filaments, which join with those from 

 the glosso-pharyngeal, superior laryngeal (its external branch), and sympathetic, 

 to form the pharyngeal plexus, from which branches are distributed to the muscles 

 and mucous membrane of the pharynx and the muscles of the soft palate. From 

 the pharyngeal plexus a minute filament (lingual branch) is given off, which 

 descends and joins the hypoglossal nerve as it winds round the occipital artery. 



The superior laryngeal is the nerve of sensation to the larynx. It is larger than 

 the preceding, and arises from the middle of the inferior ganglion of the pneumo- 

 gastric. It consists principally of filaments from the accessory portion of the spinal 

 accessory. In its course it receives a branch from the superior cervical ganglion 

 of the sympathetic. It descends by the side of the pharynx behind the internal 

 carotid, where it divides into two branches, the external and internal laryngeal. 



The external laryngeal branch, the smaller, descends by the side of the larynx, 

 beneath the Sterno-thyroid. to supply the Crico-thvroid muscle. It gives branches 

 to the pharyngeal plexus and the Inferior constrictor, and communicates with the 

 superior cardiac nerve, behind the common carotid. 



The internal laryngeal branch descends to the opening in the thyro-hyoid 

 membrane, through which it passes with the superior laryngeal artery, and is 

 distributed to the mucous membrane of the larynx. A small branch communicates 

 with the recurrent laryngeal nerve. The branches to the mucous membrane are 

 distributed, some in front to the epiglottis, the base of the tongue, and the 

 epiglottidean glands ; while others pass backward, in the aryteno-epiglottidean 

 fold, to supply the mucous membrane surrounding the superior orifice of the 

 larynx, as well as the membrane which lines the cavity of the larynx as low down 

 as the vocal cord. The filament which joins with the recurrent laryngeal descends 

 beneath the mucous membrane on the inner surface of the thyroid cartilage, where 

 the two nerves become united. 



The inferior or recurrent laryngeal. so called from its reflected course, is the 

 motor nerve of the larynx. It arises on the right side, in front of the subclavian 

 artery : winds from before backward round that vessel, and ascends obliquely to 

 the side of the trachea, behind the common carotid and behind or in front of tl.e 

 inferior thyroid artery. On the left side it arises in front of the arch of the 

 aorta, and winds from before backward round the aorta just beyond where the 

 remains of the ductus arteriosus are connected with it, and then ascends to the 

 side of the trachea. The nerves on both sides ascend in the groove between the 

 trachea and oesophagus, and, passing under the lower border of the Inferior con- 

 strictor muscle, enter the larynx behind the articulation of the inferior cornu of 

 the thyroid cartilage with the cricoid, being distributed to all the muscles of the 

 larynx, except the Crico-thyroid. It communicates with the Superior laryngeal 

 nerve and sends twigs to the mucous membrane below the true cords. The recur- 

 rent laryngeal, as it winds round the subclavian artery and aorta, gives off 

 several cardiac filaments. "which unite with the cardiac branches from the pneu- 



