282 



MAMMALIA. 



to one another ; but no Mammal has ever more than these 

 two sets. The Mammals with two sets of teeth are called 

 by Owen " diphyodont." 



In Man and in many other Mammals the teeth are divis- 

 ible into four distinct groups, which differ from one another 

 in position, appearance, and function ; and which are known 

 respectively as the incisors, canines, 'prccniolaTs, and molars 

 (fig. 596). "Those teeth which are imj)lanted in the pra?- 

 maxillary bones, and in the corresponding part of the lower 

 jaw, are called 'incisors,' whatever be their shape or size. 

 The tooth in the maxillary bone which is situated at or near 

 to the suture with the prtemaxillary, is the ' canine,' as is 

 also that tooth in the lower jaw which, in opposing it, passes 

 in front of its crown when the mouth is closed. The other 

 teeth of the first set are the ' deciduous molars ; ' the teeth 



Fig. 596. — Teeth of the right side of the lower jaw of the Chimpanzee (after Oweu). 

 i, Incisors ; c, Canine; fin, Prseniolars ; m, Molars. 



which displace and succeed them vertically are the 'pre- 

 molars ; ' the more posterior teeth, which are not disj^laced 

 by vertical successors, are the ' molars ' properly so called " 

 (Owen). The deciduous dentition, tlierefore, of a diphyodont 

 Mammal consists of only three kinds of teeth — incisors, 

 canines, and molars. The incisor and canine teeth of the 

 deciduous set are replaced by the teeth which bear the same 

 names in the permanent set. The deciduous " molars," how- 

 ever, are replaced by the permanent " praemolars," and the 

 " molars " of the permanent set of teeth are not represented 



