Genio-Hyo-Glossus.
Lingualis.
Hyo-Glossus.
Stylo-Glossus.
Palato-Glossus.

Dissection. After completing the dissection of the preceding muscles, saw through the lower jaw just external to the symphysis. The tongue should then be drawn forwards with a hook, and its muscles, which are thus put on the stretch, may be examined

The Genio-Hyo-Glossus has received its name from its triple attachment to the chin, hyoid bone, and tongue; it is a thin, flat, triangular muscle, placed vertically in the middle line, its apex corresponding with its point of attachment to the lower jaw, its base with its insertion into the tongue and hyoid bone. It arises by a short tendon from the superior genial tubercle on the inner side of the symphysis of the chin, immediately above the Genio-hyoid; from this point the muscle spreads out in a fan-like form, the inferior fibres passing downwards, to be inserted into the upper part of the body of the hyoid bone, a few being continued into the side of the pharynx; the middle fibres passing backwards, and the anterior ones upwards and forwards, to be attached to the whole length of the under surface of the tongue, from the base to the apex.

Relations. By its internal surface, it is in contact with its fellow of the opposite side, from which it is separated, at the back part of the tongue, by a fibro-cellular structure, which extends forwards through the middle of the organ. By its external surface, with the Lingualis, Hyo-glossus, and Stylo-glossus, the lingual artery and hypoglossal nerve, the gustatory nerve, and the sublingual gland. By its upper border, with the mucous membrane of the floor of the mouth. By its lower border, with the Genio-hyoid.

The Hyo-Glossus is a thin, flat, quadrilateral plane of muscular fibres, arising from the body, the lesser cornu, and whole length of the greater cornu of the hyoid bone, and passing almost vertically upwards, is inserted into the side of the tongue, between the Stylo-glossus and Lingualis. Those fibres of this muscle which arise from the body are directed upwards and backwards, overlapping those from the greater cornu, which are directed obliquely forwards. Those from the Jesser cornu extend forwards and outwards along the side of the tongue, under cover of the portion arising from the body.

The diiference in the direction of the fibres of this muscle, and their separate origin from different segments of the hyoid bone, led Albinus and other anatomists to describe it as three muscles, under the names of the Basio-glossus, the Cerato-glossus, and the Chondro-glossms.

Relations. By its external surface, with the Digastric, the Stylo-hyoid, Stylo-glossus, and Mylo-hyoid muscles, the gustatory and hypoglossal nerves, Wharton's duct, and the sublingual gland. By its deep surface, with the Genio-hyo-glossus, Lingualis, and the origin of the middle Constrictor muscle of the pharynx, the lingual artery, and the glosso-pharyngeal nerve.

The Lingualis is a longitudinal band of muscular fibres, situated on the under surface of the tongue, lying in the interval between the Hyo-glossus and the Genio-hyo-glossus, and extending from the base to the apex of that organ. Posteriorly, some of its fibres are lost in the base of the tongue, and others are attached to the hyoid bone. It blends with the fibres of the Stylo-glossus, in front of the Hyo-glossus, and is continued forwards as far as the apex of the tongue. It is in relation, by its under surface, with the ranine artery.

The Stylo- Glossus, the shortest and smallest of the three styloid muscles, arises from the anterior and outer side of the styloid process, near its centre, and from the stylo-maxillary ligament, to which its fibres in most cases are attached by a thin aponeurosis. Passing downwards and forwards, so as to become nearly horizontal in its direction, it divides upon the side of the tongue into two portions; one longitudinal, which is inserted along the side of the tongue, blending with the fibres of the Lingualis, in front of the Hyo-glossus; the other oblique, which overlaps the Hyo-glossus muscle, and decussates with its fibres.

Relations. By its external surface, from above downwards, with the parotid gland, the Internal pterygoid muscle, the sublingual gland, the gustatory nerve, and the mucous membrane of the mouth. By its internal surface, with the tonsil, the Superior constrictor muscle of the pharynx, and the Hyo-glossus muscle.

The Palato-Glossus, or Constrictor Isthmi Faucium, although one of the muscles of the tongue, serving to draw its base upwards during the act of deglutition, is more nearly associated with the soft palate, both in its situation and function; it will, consequently, be described with that group of muscles.

Nerves. The muscles of the tongue are supplied by the hypoglossal nerve, excepting the Palato-glossus, which receives its nerves from the palatine branches of Meckel's ganglion.

Actions. The movements of the tongue, although numerous and complicated, may easily be explained by carefully considering the direction of the fibres of the muscles of this organ. The Genio-hyo-glossi, by means of their posterior and inferior fibres, draw upwards the hyoid bone, bringing it and the base of the tongue forwards, so as to protrude the apex from the mouth. The anterior fibres will restore it to its original position by retracting the organ within the mouth. The whole length of these two muscles acting along the middle line of the tongue will draw it downwards, so as to make it concave from before backwards, forming a channel along which fluids may pass towards the pharynx, as in sucking. The Hyo-glossi muscles draw down the sides of the tongue, so as to render it convex from side to side. The Linguales, by drawing downwards the centre and apex of the tongue, render it convex from before backwards. The Palato-glossi draw the base of the tongue upwards, and the Stylo-glossi upwards and backwards.