VERTEBRATA : MAMMALIA. 649 



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

 to the suture with the prsemaxillary, 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 



Fig. 356. Teeth of the right side of the lower jaw of the Chimpanzee (after Owen). 

 i Incisors ; c Canine tooth ; pm Praemolars ; m Molars. 



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

 displace and succeed them vertically are the ' praemolars ; ' 

 the more posterior teeth, which are not displaced by vertical 

 successors, are the ' molars ' properly so called " (Owen). 

 The deciduous dentition, therefore, 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," however, are re- 

 placed by the permanent "praemolars," and the "molars" of 

 the permanent set of teeth are not represented in the decidu- 

 ous series, only existing once, and not being replaced by 

 successors. It has, however, been shown that in some diphyo- 

 dont Mammals there may be certain of the anterior maxillary 

 teeth in the permanent dentition, which are not represented 

 by any predecessors in the deciduous series. This is the case, 

 for example, with the first praemolar of the Dog. 



All these four kinds of teeth are not necessarily present in 

 all Mammals, and, as will be afterwards seen, the characters of 

 the teeth are amongst the most important of the distinctions by 

 which the Mammalian orders are separated from one another. 

 The variations which exist in the number of teeth in different 

 Mammals are usually expressed by a " dental formula," which 



