432 A MANUAL OF DENTAL ANATOMY. 



are very deeply grooved upon their sides, so that their 

 grinding surfaces are uneven. 



Their dental formula is, 



.101 4 

 1 1 C P 1 m I' 



The first tooth of the molar series is a single column, 

 whereas the deep grooving of the others divides them into 

 two columns, so that its simpler appearance, as well as 

 analogy, would indicate that it is a premolar. But no 

 succession whatever has been observed in the wombats. 



The adaptive resemblance to the dentition of the true 

 Rodents is exceedingly close, though the Wombat is an 

 undoubted Marsupial ; and the very closeness of the imita- 

 tion is an exemplification of the fact that adaptive charac- 

 ters are very apt to mislead, if used for the purposes of 

 classification. 



Extinct wombats, of very much larger size than the 

 recent species, are found in the later tertiary deposits of 

 Australia. 



Amongst the Marsupials there is a pretty little arboreal 

 creature (Tarsipes), not larger than a small rat, which sub- 

 sists upon insects and the nectar of flowers, which it reaches 

 by means of a long protrusible tongue. Its molar teeth 

 are rudimentary, variable in number, and are soon shed ; 

 the lower incisors, which are procumbent, are however re- 

 tained, as are a few small teeth which are opposed to them 

 above. 



The wonderful diversity of the forms into which the 

 Marsupials have branched out in Australia seems to prove 

 that they have been established in that region, and have 

 been without the competition of more highly organised 

 placental Mammals, for a prodigious length of time j and 

 one cannot better conclude the very brief survey of the 

 teeth of Mammalia which has been attempted in this volume 



Upper and lower teeth of Wombat (Phascolomys wombat). 



