274 ELEMENTARY ANATOMY. [LESS. 



be of various degrees of vascularity. 1 On the other hand, 

 the structure of the teeth may be much simpler than in 

 man in his own class, as, e.g., in the Sloths and Armadillos, 

 where the teeth are formed of dentine and cement only, 

 being destitute of enamel. 



The best example of great complexity of structure of a 

 Mammalian tooth is that exhibited by one of the molars of 

 the Indian Elephant. 



Such a tooth consists of a number of narrow transverse 

 plates of dentine, each plate being capped with enamel, and 

 the interspaces between the plates being filled up with a 

 quantity of cement, as if this material had been poured round 

 and between the plates, and had there solidified. As the tooth 

 wears, it assumes the transversely ridged appearance before 

 noticed, which is an effect of the different densities of the 

 component tissues. 



Thus the enamel, being harder than either the dentine or 

 the cement, stands up a little along each front and hind 



FIG. 252. GRINDING SURFACE OF LOWER MOLAR OF INDIAN ELEPHANT. 



(After Omen.) 



d, d, two of the vertical plates of "dentine" (each surrounded by "enamel"), 

 which are connected together by the "cement." 



margin of each transverse plate ; and in this way, proceeding 

 from either end of the tooth along its grinding surface, we 

 successively meet with layers thus arranged : Cement, 

 enamel, dentine, enamel, cement, enamel, dentine, enamel, 

 cement, &c. 



1 7.1?. may be more or less permeated by canals for nutritive fluid, which are 

 larger than the dentinal tubes existing in man. 



