TONGUE 795 a more or less distinct longitudinal furrow on the median line, from which extend out- ward and forward numerous other lines whose angle of union points backward ; the posterior third is smooth and without compound papil- lae, exhibiting a few simple ones and the nodu- lar eminences of the numerous muciparous glands ; in front of this is a V-shaped ridge, the angle directed backward, formed by two converging lines of button-like eminences, the circumvallate papillae; in front of these, and occupying the anterior two thirds of the organ, are the fungiform and conical or villiform pa- pill, the former spheroidal and scattered, the latter very numerous. The osseous support of the tongue is the U-shaped or hyoid bone, consisting of a base or median body, two greater and two lesser cornua, and placed in the neck between the lower jaw and the thy- roid cartilage ; it is the homologue of a very complex apparatus in the lower vertebrates. The muscles constitute the chief bulk of the tongue; they are arranged in a complicated manner, so as to support each other, rendering the movements of the organ exceedingly va- ried and extensive ; they are attached to the submucous fibrous tissue, which is firm and thick on the superior surface. The mucous membrane is invested with a delicate scaly epithelium, the superficial layer of which read- ily and constantly falls off. The papillae are much like those of the skin, most being com- pound organs, in their nervous and vascular supply. The circumvallate papillae are 6 to 10 in number, and sometimes % in. in diameter ; the fungiform are V to ^V m - ^ n diameter, and vary greatly in number, perhaps accounting for the well known diversity in the acuteness of the sense of taste in different individuals ; the filiform are the most numerous, closely set like the pile of velvet, covering the anterior two thirds of the tongue, and the seat of what is called the fur ; their epithelium frequently breaks up into hair-like processes, having their imbrications directed backward, which mark a physiological distinction between the circum- vallate and fungiform papillae and the filiform and conical ones. The conical papillae are gen- erally regarded as tactile, the fungiform and circumvallate as gustatory (acutely tactile), and the filiform as the homologues of the recurved spines of the tongue of the cats, and as princi- pally concerned in regulating the movements of the food in order to bring it within the reach of the muscles of deglutition. The principal arteries of the tongue are the lingual branches of the external carotid;, the sensory nerves are the lingual branch of the fifth pair or trifacial and the glossopharyngeal, distributed respec- tively to the anterior and posterior portions, and the motor nerve is the hypoglossal; for their functions see TASTE. The 'tongue in fishes is rudimentary, and not endowed with any great sensibility or motor power ; in rep- tiles it varies greatly in length, size, and mov- ability, being in some immovable or short and thick, in some remarkable for slenderness and length (as in serpents), and in others for pro- tractility (as in the chameleon and frog); in them it is usually an organ of prehension and not of sensation. The tongue in birds is also prehensile and not gustatory, and generally FIG. 1. Papilla circumvallata of Man, In transverse and ver- tical section. A. Proper papilla. B. Wall. a. Epithelium. c. Secondary papillae. 6, 6. Nerves of the papilla and of the wall. (Magnified about 10 diameters.) provided at the base with numerous spines directed backward to prevent the return of food ; though itself incapable of elongation, it may be remarkably protruded by the action of the muscles attached to the very long and movable hyoid bones. In some mammals, as the giraffe and ant-eater, it is capable of great elongation, and is an important organ of pre- hension ; the recurved spines of the cats have been referred, to, and constitute efficient in- struments for cleaning flesh from bones and for combing their fur. In man the tongue keeps the food during mastication within the range of the teeth, collects it from all parts of the mouth preparatory to swallowing it, and is also concerned in the commencement of de- glutition ; and it is a principal organ of articu- lation. It is liable to inflammation, enlarge- ment, atrophy, ulcerations, tumors, and ma- lignant diseases. The fur in disease depends on a sodden and opaque condition of the epi- thelium of the filiform and conical papillae, arising from an alteration of the mucus and FIG. 2. A. Fungiform Papilla, showing the secondary papilla on its surface, and at a its epithelium covering them over. (Magnified 25 diameters.) B. The capillary loops of the simple papillae of A, injected: a, artery; v, vein. The groove around the base of some of the fungiform papillae is represented, as well as the capillary loops (c. c) of some neighboring simple papillae. (Magnified 16 diameters.) saliva of the mouth, the bright red color of the fungiform papillae presenting a striking con- trast ; the amount, color, and arrangement of the fur are symptomatic of various morbid changes in the system, of interest to the physi- cian, though there is great variety within the
