138 



THE VITAL FUNCTIONS. 



their surfaces opposite to each other alternately on 

 both sides. Fig. 27.9 shows the grinding surface of 

 the tooth of a Sheep, where the layers of bone are 

 not apparent; there being only two layers of enamel 

 (e), and one of crusta petrosa (c). 



These three component parts are seen to most 

 advantage in a vertical and longitudinal section of 

 the grinding tooth of the elephant, in which they 

 are more completely and equally intermixed than 

 in that of any other animal. Fig. 281 presents a 

 vertical section of the grinding tooth of the Asiatic 

 Elephant, in the early stage of its growth, and 



highly polished ; so as to exhibit more perfectly its 

 three component structures. The enamel, marked 

 E, is formed of transverse fibres ; the osseous, or 

 innermost structure is composed of longitudinal 

 plates : the general covering of crusta petrosa, c, is 

 less regularly deposited : p is the cavity which had 

 been occupied by the pulp. In this tooth, which is 

 still in a growing state, the fangs are not yet added; 

 but they are, at one part, beginning to be formed. 



