TEETH. 



707 



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demonstrating the identity of its dental structure with 

 that of the Sloth, has yielded us an unerring indication of 

 the true nature of its food." 



The teeth of Man and of most of the higher animals 

 are composed of three different 

 substances, Dentine (known as 

 ivory in the tusk of the elephant), 

 Enamel, and Cementum, or crusla 

 petrosa. These are variously dis- 

 posed, according to the purposes 

 which the tooth is to serve : in 

 Man the whole crown of the 

 tooth is covered with enamel, 

 shown in the darker marginal 

 part of fig. 340 ; its root or fang 

 is covered with cementum, 

 whilst the substance or body of the tooth is composed of 

 dentine. 



In the human suhject, two sets of teeth are developed, 

 the milk and permanent : the first are formed from one 





Fig. 339. — Portion of an enchon- 

 dromatous mass, nucleated cells, 

 and fibrous tissue. 



Fig. 340. — Sections of Human Molar Tooth (magnified 50 diameters) 

 1, Vertical Section. 2, Horizontal Section. 



set of hulbs, which in time shrink, and let the teeth fall 

 out; the permanent set is then produced from new bulbar, 



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