426 A MAN.UAL OF DENTAL ANATOMY. 



excess of the number of the typical mammalian dentition, 

 having 



.4 1 3 6 



1 3 c r p 3 m o 



In the Phalangers, nocturnal arboreal animals found in 

 Australia and a part of the Malay Archipelago, the canines, 

 though present, are feeble ; an interspace also separates the 

 incisors from the molar series. 



The lower incisors, reduced to a single pair, are procum- 

 bent, and grow from persistent pulps ; and a slight exagge- 

 ration of the peculiarities of the dentition of the Phalangers 

 brings us to that of the Kangaroo Rats. 



The name " Kangaroo Rats " (Hypsiprymnus) is applied 

 to a genus consisting of about a dozen species ; they are all 

 small creatures, not much larger than rabbits, but having 

 the general proportions of kangaroos. They are quiet, 

 gentle little creatures, of strictly herbivorous habits, and 

 they are interesting to the odontologist as possessing a 

 dentition which throws some light upon several anomalous 

 extinct forms, whose habits and affinities have been the 

 subject of much controversy. 



The dental formula is 



i I c 1 p 1 m t 

 1 J 1 4 



The first pair of upper incisors are sharply pointed, are 

 directed nearly vertically downwards, and grow from per- 

 sistent pulps. The second and third do not grow from 

 persistent pulps, and their worn crowns do not attain to the 

 same level as those of the first pair. 



All three pairs are antagonised by the single pair of large 

 procumbent lower incisors, of which the sharp points meet 

 the first pair of upper incisors, while the obliquely-worn 

 surface behind the cutting edges impinges against the second 

 and third upper incisors. 



The arrangement of the incisors, and the sharpness of 



