THE TONGUE. 313 



tubules which, radiating from the pulp cavity, perforate it 

 throughout, finally ending in minute branches which open 

 into irregular cavities, the interglobular spaces, which lie 

 just beneath the enamel or cement. At their widest ends, 

 close to the pulp cavity, the dentinal tubules are only 

 about 0.005 millimeter (j-gVir f an inch) in diameter. 

 The cement is much like bone in structure and composition, 

 possessing lacunae and canaliculi but rarely any Haversian 

 canals. It is thickest at the tip of the fang and thins 

 away towards the cervix. Enamel is the hardest tissue in 

 the Body, yielding on analysis only from two per cent to 

 three per cent of organic matter, the rest being mainly 

 calcium phosphate and carbonate. Its histological ele- 

 ments are minute hexagonal prisms, closely packed, and set 

 on vertically to the surface of the subjacent dentine. It is 

 thickest over the free end of the crown, until worn away by 

 use. Covering the enamel in unworn teeth is a thin struc- 

 tureless horny layer, the enamel cuticle. 



The Tongue (Fig. 95) is a muscular organ covered with 

 a mucous membrane, extremely mobile, and endowed not 

 only with a delicate tactile sensibility but with the ter- 

 minal organs of the special sense of taste; it is attached 

 by its root to the hyoid bone. Its upper surface is covered 

 with small eminences or papillae, much like those more 

 highly developed on the tongue of a cat, where they are 

 readily felt. On the human tongue there are three kinds 

 of papillae, the circumvaUate, the fungiform, and the fill*, 

 form. The circumvaUate papillae, 1 and 2, the largest 

 and least numerous, are from seven to twelve in number 

 and lie near the root of the tongue arranged in the form of 

 a V with its open angle turned forwards. Each is an ele- 

 vation of the mucous membrane, covered by epithelium, 

 and surrounded by a trench. On the sides of the papillae, 

 imbedded in the epithelium, are small oval bodies (Fig. 155)* 

 richly supplied with nerves and supposed to be concerned 

 in the sense of taste, and hence called the taste buds 

 (Chap. XXXIV.). The fungiform papillce, 3, are rounded 

 elevations attached by somewhat narrower stalks, and found 

 all over the middle and fore part of the upper surface of 



* P. 571. 



