Inferior pharyngeal branch (ramus pharyn geus inferior ).—This branch arises a very little below the last, and runs parallel to it and across the anterior surface of the internal carotid. It is joined by a considerable bmnch from the superior ganglion of the sympathetic, which generally forms an arch with it around the ascending pharyngeal artery. It soon divides itself into different branches which are distri buted upon the lower part Of the middle con strictor muscle, and over the whole of the inferior constrictor, and anastomoses with the twigs of the other nerves found on the surface of these muscles.
Valentin describes under the name of middle pharyngeal nerves (ranzi pharyngei medli seu tenuiores n. v.) some small filaments arising from the anterior surfa.ce of the vagus imme diately below the superior pharyngeal, and which pass forwards to join the pharyngeal branches of the glosso-pharyngeal. The free anastomosis of the nerves we have mentioned, viz. the glosso-pharyngeal and sympathetic, with the numerous subdivisions of the pharyngeal branches of the vagus, intermixed with a few twigs from the superior laryngeal, and also with some small filaments from the upper part of the cervical plexus of nerves, and an occa sional twig from the hypo-glossal, form an elongated and intricate plexus (plexus pharyn geus) upon the lateral surface of the pharynx. (See article GLOSS-PHARYNGEAL NERVE.) Superior laryngeal branch (ramus luryngeus superior) arises from the inner side of the vagus, about four or five lines below the superior pharyngeal branch, and from the upper and inner part of the second or inferior ganglion. It is considerably larger than the pharyngeal branch, and in the first part of its course pro ceeds almost directly inwards, then inwards and downwards, passing behind the internal carotid and in front of the longus colli muscle.° While it is behind the carotid it generally divides into its two branches, the internal and external. The internal is much the larger and more important, crosses the lateral part of the middle constrictor of the pharynx obliquely downwards, forwards, and inwards, joins itself to the laryngeal branch of the superior thyroid artery and runs along its upper edge, passes between the lower margin of the os hyoides and upper margin of the thyroid cartilage, and reaches the upper edge of the larynx by per forating the thyro-hyoid ligament posterior to the external edge of the thyro-hyold muscle, above the upper edge of the inferior constrictor and below the lower edge of the rniddle con strictor of the pharynx, and a little in front of the round ligament connecting the superior cornu of the thyroid cartilage to the larger comu of the hyoid bone. Sometimes one or two small twigs pass between the trunk of the vagus and the superior laryngeal soon after the origin of the latter, and the external branch of the superior laryngeal occasionally comes directly from the trunk of the vagus, a little below the origin of the internal branch. NVhile the superior laryngeal nerve is passing behind the internal carotid, it sends off several small twigs, some of which communicate with the pharyngeal plexus, a few pass downwards and throw themselves into some of the cardiac nerves, and the greater part run upon the sur face of the internal and external carotids, and assist in forming, with the inore numerous branches from the sympathetic, the- arterial plexus of nerves winding round the carotid arteries and their branches.
External branch of the superior laryngeal. It is strengthened by some twigs from the superior ganglion of the sympathetic, passes downwards and forwards over the inferior con strictor muscle of the pharynx and lateral surface of the larynx, gets below the outer edge of the sterno-thyroid, and continues its course below it and the thyro-hyoid muscle. It gives
some twigs to the inferior constrictor muscle, some, filaments also to the upper part of the sterno-hyoid and thyroid muscles, and to the thyroid body. The continuation of the nerve after sending a twig downwards to anastomose with another twig, from the inferior laryngeal nerve behind the thyroid body, ultimately ter minates in the crico-thyroid muscle.t Internal branch of the superior laryngeal. A.s soon as this branch has perforated the thyro hyoid ligament and reached the outer surface of the mucous membrane immediately beneath it, it divides into numerous branches which are flattened and radiating, some passing tip wards and forwards towards the base of the tongue and sides of the epiglottis, others for wards, downwards, and inwards in the aryteno epiglottidean folds to the surfaces of the epi glottis, and others downwards upon the posterior surface of the larynx. The branches which proceed forwards and upwards are small and pass onwards to the glosso-epiglottidean folds; and while some of their filaments terminate in these folds and in the mucous membrane at the lateral and back part of the tongue, others turn inwards and are distributed upon the sub mucous glands and the mucous covering of the anterior and upper part of the epiglottis. Several pretty strong branches pass forwards and inwards in the aryteno-epiglottidean folds to the side of the epiglottis. Some of these proceed upon its anterior surface and are there distributed upon the mucous membrane and the subtnucous glands, sending also a few filaments through small apertures in the epi glottis to be ramified in the mucous membmne on its posterior or laryngeal surface; while other branches pass upon the posterior aspect of the epiglottis,—some of them occupying notches on its outer edge,—and are distributed upon the submucous glands and mucous mem brane covering that surface. A few branches proceed downwards and forwards over the outer surface of the lining mucous membrane of the larynx, send some filaments to the laryngeal sac, and may be traced as far as the inferior or true vocal chords. A long slender branch passes downwards on the outer surface of the thyro-arytenoid muscle, and between it and the inner surface of the thyroid cartilage, and fre quently anastomoses with an ascending branch of the recurrent or inferior laryngeal. One or two slender filaments enter the thyro-arytenoid muscle, and these, after a long and winding. course among the fibres of that muscle and those of the crico-arytenoideus lateralis, ulti mately run to the mucous membrane of the larynx. A pretty large branch runs backwards in the posterior part of the thyro-arytenoid fold of mucous membrane, transmitting at the same time a few filaments downwards; and on reach ing the arytenoid cartilage it sends seveml filaments upon the posterior surface of the proper arytenoid muscles, and continuing its course downwards between the mucous mem brane of the pharynx and the crico-arytenoideus posticus muscle, it anastomoses with one of the posterior ascending branches of the recurrent. Tbe greater part of the filaments which enter among the fibres of the arytenoideus posticus and transversus muscles may be traced to the mucous membrane of the larynx, and only a very few appear to terminate among the mus cular fibres; others anastomose with arytenoid branches of the superior laryngeal of the opposite side, and with the• arytenoid branch of the recurrent; and occasionally a filament perforates the arytenoid cartilage to reach the inner surface of 'the larynx.