Mucous glands.—These are largest and most abundant at the base of the tongue, where they occupy the space behind the circum vallate papillm, and lie immediately beneath the surface, which they raise in nodular emi nences. The most anterior of them form a V-shaped ridge, the counterpart of that formed by the circumvallate papillm, from which they are separated by a corresponding furrow. These structures, which are true mucous glands, analogous to the buccal and labial, are of an oval or roundish lenticular shape : in front of the epiglottis they are gradually lost. Each gland is surmounted by a distinct orifice, most conspicuous in the most posterior of them, opening into a little crypt, generally closed and collapsed, but dilatable so as to be large enough to contain a mustard-seed, and into the bottom of these crypts the minute ducts of the glands open. Some of these crypts I have found extending into long and capacious canals, branching in dif ferent directions, and undermining the surface. I have traced some of them half or three quarters of an inch before they have termi nated in their blind extremities : their surface is quite smooth, and the orifices of the ducts of neighbouring glands might be seen termi nating in different parts of it. They probably act as reservoirs, and permit some accumula tion of the secretion, and also prevent the orifices of the glands from infarction by the matters passing over the surface. Similar glands, but smaller, are seen along the sides of the tongue, particularly near the base ; and under the tip a small aggregation of them, first described by Nuck, may generally be de tected : they are about eight or ten in num ber, much smaller than those at the base, situated on each side of the median furrow, and each surmounted by a little orifice. The true glandular nature of all these structures is proved by microscopical examination : they are seen to be true conglomerate glands, their ultimate follicles filled with an abundant se creting epithelium.
Vessels of the vascular supply of this organ, which is large in proportion to its size, is derived mainly from its proper ar tery, the lingual, but it receives some small branches at its sides and base from the inferior pharyngeal and palatine. The lingual artery arises from the external carotid, between the inferior thyroid and the facial : it passes up wards and inwards, at first superficial, covered only by the integument and fascim, to reach the posterior border of the hyoglossus muscle, beneath which it passes to its anterior border, where it breaks up into its terminal branches, the sublingual and the ranine. In the first part of its course it lies on the middle constrictor of the pharynx ; in the second part it is covered by the hyoglossus and mylohyoid muscles, and lies on the middle constrictor and genio glossus. Previous to passing beneath the posterior border of the hyoglossus the artery is crossed by the hypoglossal nerve, which, at first placed below it, now rises above it ; the hyoglossus muscle then separates the two, the nerve lying outside of it and the artery beneath it, but at its anterior border they are again in relation ; the nerve, however, is now inferior, having crossed the course of the artery while beneath the hyoglossus. Its branches are, 1st, a hyoid branch, passing along the upper margin of the hyoid bone, corre sponding to a branch of the superior thyroid running along the under margin of the bone, with which and with its fellow of the opposite side it anastomoses ; 2dly, the dorsalis linguce branch, ascending from the artery in the se cond part of its course, supplying the side and dorsum of the tongue ; 3dly, the sublingual, one of its two terminal branches, passing downwards and outwards from the anterior margin of the hyoglossus to be distributed to the sublingual gland, cellular tissue, and mu cous membrane adjacent ; 4thly, the ranine, which may be regarded as its continuation, passing upwards and inwards in immediate relation with the genioglossus to the tip, where it anastomoses with its fellow. That
the communication of the arteries of the opposite sides of the tongue is not very free, is shown by the imperfect injection of one side when the injection is made into the carotid of the opposite side : it is free enough, however, to make the ligature of the artery of one side of little service in stopping haemorrhage of that side, the supply from the other being sufficient to keep it up.
Nerves of the tongue. — The tongue is sup plied with nerves from three sources, two sentient— the lingual branch of the fifth, and the glosso-pharyngeal, and one motor — the ninth or hypoglossal nerve. The lingual or gus tatory nerve, one of the three great branches into which the sensory portion of the inferior maxillary division of the fifth breaks up after its emergence through the foramen ovale, passes down, at first between the external pterygoid muscle and the small muscles of the palate, then between the two pterygoids, then between the internal pterygoids and the jaw, finally escaping from between these two at the anterior border of the muscle ; it then runs downwards and forwards, under the pro tection of the jaw, to the side of the tongue, crosses the mylohyoid attachment of the superior constrictor, then passes forwards beneath the sublingual gland and to the outer side of the ranine artery, to terminate at the tip of the tongue. The numerous small branches that are distributed to the conical and fungiform papillm may be seen ascending from the nerve whilst beneath the tongue, passing upwards and forwards through the substance of the organ to the mucous surface. The other nerve of sensation, the glosso-pha ryngeal, the smallest and most anterior di vision of the eighth pair, emerges from the skull through the foramen lacerum jugulare by a distinct fibrous canal ; it then descends between the jugular vein and internal carotid, passing forwards, in front of that artery and beneath the styloid process and muscles aris ing from it, to the anterior border of the stylo pharyngeus, between that muscle and the styloglossus ; it then passes under the hyo glossus, beneath which and below the tonsil it divides into its branches for the supply of the gland and the tongue: its arch across the neck is below of the lingual, and above the hypoglossal, but deeper seated than either. The branches to the tongue are distributed to the circumvallate papillm, and the mucous surface behind them. The ninth, or hypo glossal nerve, the motor nerve of the tongue, after escaping from the skull through the an terior condyloid foramen, lies at first deep, between the internal jugular vein and carotid artery ; coming forward between them it be comes superficial, and forms an arch across the neck below, and parallel to, the digastric muscle, hooks round the occipital artery, and passes beneath the mylohyoid muscle, but superficial to the hyoglossus, at the anterior border of which it pierces the fibres of the genioglossus, and divides into its branches for the supply of this and the other muscles of the tongue : its relations to the lingual artery have been mentioned. For a more detailed account of these nerves, of their relations, branches, and the experiments on the results of which the present amount of our knowledge as to their function is based, the reader is referred to the articles FIFTH NERVE, EIGHTH NERVE, NINTH NERVE, and TASTE.