480 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 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 suc- 

 cessors. 



Fig. 185. Teeth of the right side of the lower jaw of the Chimpanzee (after Owen), 

 z Incisors ; c Canine teeth : pm Prsemolars ; m Molars. 



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 distinc- 

 tions 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. 



According to Owen, the typical permanent dentition of a 

 diphyodont Mammal would be expressed by the following 

 formula : 



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. 



