546 MANUAL OF ZOOLOGY. 



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 " prsemolars," 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. 



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 



pill 



Fig. 235. Teeth of the right side of the lower jaw of the Chimpanzee (after Owen). 

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



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

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

 easily-recognised form. 



According to Owen, the typical permanent dentition of a 

 diphyodont Mammal would be expressed by the following 

 formula : 



44 33 



. p m . m _ .. 



44' 33 



The four kinds of teeth are indicated in such a formula by the 

 letters incisors /', canines c, praemolars pm, molars m. The 

 numbers in the upper line indicate the teeth in the upper jaw, 

 those in the lower line stand for those in the lower jaw ; and 

 the number of teeth on each side of the jaw is indicated by 

 the short dashes between the figures. 



