100 MAMMALIAN DENTITION 



in this being taken by an elongation of the metacone. Even in 

 the two anterior molars the metacone-metastyle shear is greatly 

 reduced and in the second and third it is nonexistent. The 

 needle-like appearance of the cusps is lost and since the molars 

 are quadrilateral there is but little space between them for 

 the reception of the trigonid of the lower molars. In this there 

 is a marked difference from the pattern and relations in Talpa 

 and Phascologale. In conformity with this construction of the 

 upper teeth the protoconid on the lower molars is greatly 

 reduced. The protoconid-paraconid shear is found only upon 

 the first molar. In other respects the lower teeth call for no 

 special description. The reduction in size of the molars in both 

 jaws from the first backward is an example of specialization. 

 The glenoid fossa compared Avith that of Phascologale is com- 

 paratively shallow to allow for freer rotary movement in asso- 

 ciation with the omnivorous adaptation of the teeth. 



Perhaps the most significant family of the Dilambdodonts is 

 that of the Tupaiidae or Tree Shrews which are of special im- 

 portance because of their relationship to the Primates. They 

 differ from other Insectivora in many features, for example, 

 the orbit instead of being open laterally is encircled by a ring 

 of bone as in Primates. The example chosen is Tupaia tana, 

 a Bornean Tree Shrew (Fig. 31). Its diet consists of insects 

 and fruit and the dentition is therefore insectivorous-omniv- 

 orous. The tooth formula is: 



l|,C~,p|,M|. total 38. 



The third upper incisor and the first premolar of both jaws 

 in the ancestral dentition have been lost. The markedly pro- 

 cumbent lower incisors, the reduced upper canines and the 

 increase in size backward of the premolars are noteworthy. 

 The upper molars except the last show the styles plainly al- 

 though the metacone-metastyle shear is absent. The hypocone 

 is more developed than in Talpa but less pronounced than in 

 Hylomys. Each lower molar shows a small but distinct para- 



