Chap. XXI.] 



171 



CHAPTER XXI. 



TEETH. 



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

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

 dentine forming the real 



matrix of the whole 

 tooth, and surrounding 

 the pulp cavity both of 

 the crown and fangs, 

 and (c) the cement, or 

 crusta petrosa, or sub- 

 stantia osteoidea. 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- Fig . m-Longitudiuai Section 



matic elements, the through the Preemolar Tooth of 



enamel prisms placed Jf a ' niel: 6> dentine crustfi 

 closely, and extending in 



