404 MAMMALIA. 



respectively as the incisors, canines, prcemolars, and molars 

 (fig. 335)- "Those teeth which are implanted in the prae- 

 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 prasmaxillary, 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 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 



PI* 



Fig. 335. Teeth of the right side of the lower jaw of the Chimpanzee (after Owen). 

 * Incisors ; c Canine ; fm Praemolars ; m Molars. 



molars. The incisor and canine teeth of the deciduous set are 

 replaced by the teeth which bear the same names in the per- 

 manent set. The deciduous " molars," however, are replaced 

 by the permanent " praemolars," and the " molars " of the per- 

 manent set of teeth are not represented in the deciduous series, 

 only existing once, and not being replaced by successors. 



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 

 presents the " dentition " of both jaws in a condensed and 

 easily-recognised form. 



