Chap. XXL] 



CHAPTER XXL 



THE TEETH. 



227. A HUMAN tooth, adult and milk-tooth, consists 

 (Fig. 102) of (a) the enamel covering the crown, (6) 

 the dentine forming the 



bulk of the whole 

 tooth, and surrounding 

 the pulp-cavity both of 

 the crown and fangs, 



(c) the pulp-cavity, and 



(d) the cement or crusta 

 petrosa. This cement 

 covers ^the outside of 

 the dentine of the 

 fang or fangs, in the 

 same way as the enamel 

 covers the dentine of the 

 crown. The crusta pe- 

 trosa is covered on its 

 outside by a dense fibrous 

 tissue acting as a perios- 

 teum to it, and is fixed 

 by it to the inner surface 

 of the bone forming the 

 wall of the alveolar 

 cavity. 



228. The enamel 

 (Fig. 103) consists of 



thin microscopic pris- 



matic elements, the 



enamel prisms placed 



closely, and extending in 



102. Longitudinal 



the Pr8emolar 



a, Enamel: 5, dentine ;C , crusta potrosa; 



