TKKTII. 



217 



well-developed alveoli of the jaw-bones, and there are no longer any 

 teeth on the roof of the palate. The canine, which is most largely 

 developed in Carnivora, usually lies in a continuous series with 

 the incisors, which are situated in the anterior part of the jaws 

 (premaxilla in upper jaw). The premolars follow behind the canine, 

 the space usually present between them being called the diastema, 

 and then come the molars, which lie mainly in the posterior part of 

 the jaw. 1 



The incisors are usually chisel-shaped, while the canines, in 

 those cases where they are most largely developed (Carnivora), 



FIG. 177.- DENTITION OF THE HEDGEHOG (Erinaceus curopceus). (The teeth of 

 both jaws from the side, and those of the tipper jaw from below. ) 



?', incisors ; pm, premolars ; m, molars, 



possess a pointed, conical form, and are more or less curved. The 

 form of the premolar and molar teeth may be derived from that 

 of the incisors and canines ; originally two lateral and a median 

 cutting-edge can be distinguished in all, these edges having become 

 gradually metamorphosed phylogenetically for mastication in the 

 case of the grinding teeth. In the course of further development 

 the whole grinding surface becomes reduced to the same level, 

 and appears more or less flattened or tubercular. 



In describing the teeth of a Mammal it is convenient to make use of a 

 dental formula in which their number and arrangement can be seen at a 



1 The premolars are those teeth which correspond in position with the deciduous 

 milk molars, the molars proper having no predecessors. 



