232 



ELEMENTARY PHYSIOLOGY 



there being two cusps on the inner side and three on the 

 outer. Each tooth presents a crown, which is visible in 

 the cavity of the mouth, where it becomes worn by 

 attrition with the tooth opposite to it and with the food ; 

 and one or more fangs, which are buried in a socket 

 furnished by the jawbone and the derma of the dense 

 nmcous membrane of the mouth, which constitutes the 

 gum. The line of junction between the crown and the 



Fig. 70. 



A, vertical, B, horizontal section of a tooth. — a, enamel of the crown ; 

 6, pulp cavity ; c, cement of the fangs ; d, dentine. (Magnified about 

 three diameters.) 



fang is the neck of the tonth. Tn the interior of the 

 tooth is a cavity communicating with the exterior by 

 canals, which traverse the fangs and open at their points. 

 This cavity is the pulp cavity. It is occupied and com- 

 pletely filled by a highly vascular tissue richly supplied 

 with nerves, the dental pulp, which is continuous 

 below, through the openings of the fangs, with the 

 vascular dermis of the gum which lies between the fangs 



