The Tongue (lingua).

he tongue is the principal organ of the sense of taste, and an important organ of speech; it also assists in the mastication and deglutition of the food. It is situated in the floor of the mouth, within the curve of the body of the mandible.	75
Its Root (radix linguæ base) is directed backward, and connected with the hyoid bone by the Hyoglossi and Genioglossi muscles and the hyoglossal membrane; with the epiglottis by three folds (glossoepiglottic) of mucous membrane; with the soft palate by the glossopalatine arches; and with the pharynx by the Constrictores pharyngis superiores and the mucous membrane.	76
Its Apex (apex linguæ tip), thin and narrow, is directed forward against the lingual surfaces of the lower incisor teeth.	77
Its Inferior Surface (facies inferior linguæ under surface))i s connected with the mandible by the Genioglossi; the mucous membrane is reflected from it to the lingual surface of the gum and on to the floor of the mouth, where, in the middle line, it is elevated into a distinct vertical fold, the frenulum linguæ. On either side lateral to the frenulum is a slight fold of the mucous membrane, the plica fimbriata, the free edge of which occasionally exhibits a series of fringe-like processes.	78
The apex of the tongue, part of the inferior surface, the sides, and dorsum are free.	79
The Dorsum of the Tongue (dorsum linguæ) (Fig. 1014) is convex and marked by a median sulcus, which divides it into symmetrical halves; this sulcus ends behind, about 2.5 cm. from the root of the organ, in a depression, the foramen cecum, from which a shallow groove, the sulcus terminalis, runs lateralward and forward on either side to the margin of the tongue. The part of the dorsum of the tongue in front of this groove, forming about two-thirds of its surface, looks upward, and is rough and covered with papillæ; the posterior third looks backward, and is smoother, and contains numerous muciparous glands and lymph follicles (lingual tonsil). The foramen cecum is the remains of the upper part of the thyroglossal duct or diverticulum from which the thyroid gland is developed; the pyramidal lobe of the thyroid gland indicates the position of the lower part of the duct.	80
The Papillæ of the Tongue (Fig. 1014) are projections of the corium. They are thickly distributed over the anterior two-thirds of its dorsum, giving to this surface its characteristic roughness. The varieties of papillæ met with are the papillæ vallatæ, papillæ fungiformes, papillæ filiformes, and papillæ simplices.	81