200 COMPARATIVE ANATOMY 



The shape of a tooth is determined by that of the tooth-germ. If 

 the layer of ameloblasts is folded, the enamel is correspondingly modified, 

 and teeth such as those of ruminants and elephants, which become 

 ridged by wear as the result of the difference in hardness of enamel and 

 dentine, owe this adaptive characteristic to the folding of the ameloblast 

 and odontoblast layers. The multiplication of roots as in molar teeth is 

 produced by the budding of the odontoblast layer of the dental papilla. 



