DENTITION. 139 



The same tooth in its usual state, as worn by mas- 

 tication, gives us a natural and horizontal section 

 of its interior structure, in which the plates of 

 white enamel are seen forming waved ridges. 

 These constitute, in the Asiatic Elephant, a series 

 of narrow transverse bands (Fig. 283) ; and in the 

 African Elephant, a series of lozenge-shaped lines 

 (Fig. 282), having the ivory on their interior, and 

 the yellow crusta petrosa on their outer sides; which 

 latter substance also composes the whole circum- 

 ference of the section. 



§ 4. Formation and Developement of the Teeth. 



Few processes in animal developement are more 

 remarkable than those which are employed to form 

 the teeth ; for they are by no means the same as 

 those by which ordinary bone is constructed ; and 

 being commenced at a very early period, they 

 afford a signal instance of Nature's provident anti- 

 cipation of the future necessities of the animal. 

 The teeth, being the hardest parts of the body, 

 require a peculiar system of operations for giving 

 them this extraordinary density, which no gradual 

 consolidation could have imparted. The formation 

 of the teeth is in some respects analogous to that of 

 shell ; inasmuch as all their parts, when once depo- 

 sited, remain as permanent structures, hardly ever 

 admitting of removal or of renewal by the vital 

 powers. Unlike the bones, which contain within 

 their solid substance vessels of different kinds, by 

 which they are nourished, modified, and occasion- 

 ally removed, the closeness of the texture of the 



