The tongue is a solid conical muscular organ, covered partially by the mucous membrane, and lies partly in the oral cavity and partly in the pharynx. a. It ACTS as an organ of taste, and helps in masti­cation, deglutition and speech.b. It is sometimes utilised in gestures and postures of facial expression.c. It helps in moistening the lips, and acts as a DUMPING ground for placing the postage stamps. d. In some lower animals (e.g. dog) it is used for thermo-regulation by panting.e. Sometimes tongue-prints displaying the pattern of lingual papillae are used in medico­legal purposes for personal identification.f. Clinically, it acts as a mirror in various disturbances of alimentary tract.Presenting parts: The tongue PRESENTS a tip (or apex), base dorsal and inferior surfaces, two lateral margins and a root (Fig. 11.8).Tip:It is directed forward in contact with the incisor teeth.: Base:It is directed backward towards the oropharynx and is formed by the posterior one-third of the tongue. The base is connected to the epiglottis by a median and a pair of lateral glosso-epiglottic folds. On each side of the median fold there is a depression known as the epiglottic vallecula.Dorsal surface:It is convex on all sides, covered with mucous membrane which is moist and pink, and lined usually by the non-keratinized stratified squamous epithelium. The dorsal surface is DIVIDED by a V-shaped sulcus terminalis into anterior two-thirds (oral or presulcal part) and posterior one-third (pharyngeal or post-sulcal part) of the tongue.The sulcus passes forwards and laterally from a central depression, the foramen caecum, which indicates the commencement of the median thyroid rudiment as the thyroglossal duct. The featues of the mucous membrane of the oral and pharyngeal parts of the tongue are different.ADVERTISEMENTS: In the pre-sulcal oral part, the mucous mem­brane is adherent to the underlying muscles by the lamina propria and is provided with numerous papillae of different types. Each papilla is a projection of lamina propria covered by mucous membrane and presents the following types:(a) Vallate papillae:These are about 8 to 12 in number and arranged in a V-shaped single row immediately in front and parallel to the sulcus terminalis. Each papilla is truncated conical with the broad base directed to the surface of the tongue and is surrounded by a circular sulcus. The walls of the sulcus PRESENT taste buds, and its bottom receives the ducts of serous glands the secretion of which makes the food somewhat soluble to stimulate the taste buds. The outer wall of the sulcus is known as the vallum (Fig. 11.9).