THE ORGANS OF SENSE. 



Organs of the Senses are five in number viz. those of Touch, of Taste, of 

 Smell, of Hearing, and of Sight. The skin, which is the principal seat of the 

 sense of touch, has been described in the chapter on General Anatomy. 



THE TONGUE. 



The Tongue is the organ of the special sense of taste. It is situated in the 

 floor of the mouth, in the interval between the two lateral portions of the body of 

 the lower jaw. 



Its base or root is directed backward, and connected with the os hyoides by 

 the Hyo-glossi and Genio-hyo-glossi muscles and the hyo-glossal membrane ; with 

 the epiglottis by three folds of mucous membrane 

 which form the glosso-epiglottic ligaments ; with 

 the soft palate by means of the anterior pillars 

 of the fauces ; and with the pharynx by the Su- 

 perior constrictor and the mucous membrane. 

 Its apex or tip, thin and narrow, is directed for- 

 ward against the inner surface of the lower in- 

 cisor teeth. The under surface of the tongue is 

 connected with the lower jaw by the Genio-hyo- 

 glossi muscles ; from its sides the mucous mem- 

 brane is reflected to the inner surface of the 

 gums : and in front a distinct fold of that mem- 

 brane, the //<?>? H/ linguce, is formed beneath its 

 under surface. 



The tip of the tongue, part of the under 

 surface, its sides and dorsum. are free. 



The dorsum of the tongue is convex, marked 

 along the middle line by a raphe, which divides 

 it into symmetrical halves ; this raphe terminates 

 behind, about an inch from the base of the organ, 

 in a depression, the foramen ccecum. The ante- 

 rior two-thirds of this surface are rough and 

 covered with papillae ; the posterior third is 

 smoother, and covered by the projecting orifices 

 of numerous muciparous glands. 



Structure of the Tongue. The tongue is 

 partly invested by mucous membrane and a sub- 

 mucous fibrous layer. It consists of symmetri- 

 cal halves, separated from each other, in the middle line, by a fibrous septum. 

 Each half is composed of muscular fibres arranged in various directions, contain- 

 ing much interposed fat, and supplied by vessels and nerves. 



The mucous membrane invests the entire extent of the free surface of the 

 tongue. On the dorsum it is thicker behind than in front, and is continuous with 

 the sheath of the muscles attached to it, through the submucous fibrous layer. 

 On the under surface of the organ it can be traced on each side of the fraenum 

 through the ducts of the submaxillary and the sublingual glands. As it passes 

 over the borders of the organ it gradually assumes its papillary character. 



The structure of the mucous membrane of the tongue differs in different parts. 

 That covering the under surface of the organ is thin, smooth, and identical in 



879 



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FIG. 515. Upper surface of the tongue. 



