98 MAMMALIAN DENTITION 



1 1, Ct,Pt.m|. total 44. 

 3 14 3 



This formula is important because it represents the full 

 placental dentition. The premolars are one more and the 

 molars one less in number than in Marsupials. Only in oc- 

 casional (Otocyon, Cetacea, etc.) or in doubtful (Shrews) in- 

 stances are these numbers exceeded. Examining the teeth in 

 detail and comparing them with the dentition of Phascologale 

 the following points may be noted. The upper median incisors 

 show no procumbency or approximation of tips but are uniform 

 with the others. The lower incisors are also subequal in size 

 but are slightly procumbent. Unlike the strong upper tusk the 

 lower canine is reduced and slightly procumbent. Associated 

 with this is the exaggerated size of the first lower premolar. 

 The second, third, and fourth lower premolars progressively 

 increase in size. In the maxilla the last premolar alone at- 

 tains any considerable development: it becomes a carnassial or 

 sectorial tooth similar to but less developed than that found 

 in Carnivora. The upper molars except the last show the three 

 cusps and the three styles as in Phascologale but the protocone 

 is a low shelf -like structure and projecting behind it on the 

 first and second molars is an extension which may represent 

 the hypocone. This is doubtful however since the cusp does 

 not fit into the trigonid of the lower molar next behind. Into 

 the triangular spaces between the upper teeth pass the trigo- 

 nids of the lower molars in closure of the jaws. The last upper 

 molar exhibits no metacone-metastyle shear since there is no 

 lower tooth to occlude behind it. Each mandibular molar shows a 

 typical three-cusped trigonid with a someAvhat smaller two- 

 cusped talonid or heel immediately behind. The talonid is re- 

 duced in the third molar. In brief then the dentition of Talpa 

 as just described differs from the purely insectivorous denti- 

 tion of Phascologale in its incipient carnivorous adaptation. 



A somewhat different type of Dilambdodont dentition is 

 represented in the lesser Gymnura, Hylomys suilla dorsalis 



