250 



ELEMENTAR Y ANA TO MY. 



[LESS. 



Dentine forms the bulk of the tooth ; the dense enamel 

 coats the crown ; the cement invests the fang. 



The dentine is traversed by exceedingly minute tubes 

 which radiate into it from the pulp cavity. The enamel is 

 the hardest structure in the human body, and almost en- 

 tirely a mineral, containing but two per cent, of animal 

 substance. It is made up of minute fibres, with their ends 

 applied to the surface of the dentine of the tooth. The ce- 

 ment is more like bone ; it may take a much greater share 

 in the formation of the tooth than is assigned to it in the 

 teeth of man. 



FlG. 2l8. A, VERTICAL, B, HORIZONTAL SECTION OF A TOOTH. 



n ; b, pulp cavity ; c, cement of 

 Magnified about three diameters. 



rr, enamel of the crown; b, pulp cavity; c, cement of the fangs; d, dentine, 

 lifted i " 



17. As all know, teeth are cut. The meaning of this is 

 that, as the tooth develops, it rises out of its sac, the parts 

 superficial to its apex being absorbed. As its crown rises 

 its fang is developed. 



The teeth appear successively in two sets. First the milk- 

 teeth come into place, and afterwards the second or permanent 

 set of teeth. 



Each permanent tooth is formed in a little sac, which 

 at first is but a prolongation of the sac of that milk-tooth 

 which it is destined to succeed. 



The development of the second tooth is accompanied by 



