DENTITION. 155 



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 sub- 

 stance also composes the whole circumference 

 of the section. 



'§ 4. Fonnation and Dev elopement 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 con- 

 structed ; and being commenced at a very early 

 period, they afford a signal instance of Nature's 

 provident anticipation of the future necessities of 

 the animal. The teeth, being the hardest parts 

 of the body, require a peculiar system of opera- 

 tions for giving them this extraordinary density, 

 which no gradual consolidation could have im- 

 parted. The formation of the teeth is in some 

 respects analogous to that of shell ; inasmuch as 

 all their parts, when once deposited, remain as 

 permanent structures, hardly ever admitting of 

 removal or of renewal by the vital powers. 



