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), hav- 

 ing the ivory on their interior, and the yellow 

 crusta petiosa on their outer sides; which latter 

 substance also composes the whole circumference 

 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 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. 



