82 



MAMMALIAN DENTITION 



is necessary to examine the dentitions of two animals which 

 represent side lines in evolution. 



Trichosurns vulpecula, the true Phalanger (Fig. 23), one of 

 the so-called Australian Opossums, is an animal about the size 

 and form of a small fox. It is common everywhere in forested 



Fig. 23. — Dentition of the true Phalanger (Trichosurus vulpecula, 9.222-4). This 

 dentition indicates still more clearly than that of Petaurus the evolution of the pure 

 herbivorous type. 



regions of the continent and its diet consists of small birds and 

 leaves especially of the peppermint gum tree. The tooth 

 formula is: 



l|, C^,Pj,m|. total 38. 



The upper incisors are arranged in a somewhat carnivorous 

 rasping arch and the last premolar of both jaws is sectorial in 

 type, a form equally serviceable for cutting flesh or shoots. The 

 canines are greatly reduced and the molars bunodont and 

 roughly quadrilateral. The median lower incisors are elon- 

 gated as in the herbivorous Kangaroos and the next incisors 



