72 MAMMALIAN DENTITION 



ing lower as a pestle in a mortar. Again the trigonid of the 

 lower tooth shears behind the trigon of the upper next in 

 front. Hence the protoconid and paraconid of the lower molar 

 correspond to one blade of the shears while the metacone and 

 metastyle of the upper form the other blade. It is especially 

 important to emphasize this as a preliminary to the discussion 

 later of carnivorous adaptations in teeth. Equally important 

 is it to remember in connection with omnivorous and herbiv- 

 orous modification that the first indication of triturating action 

 is the mortar and pestle relation of the talonid with the proto- 

 cone. Once these fundamental relationships of the upper 

 and lower molars to each other are fully understood the reason 

 for the imperfect development of the last member of both series 

 becomes obvious. Having no lower molar to shear behind it 

 the last upper has developed no metacone or metastyle. Also 

 the last upper tooth being reduced and possessing an imper- 

 fect protocone the talonid of the last loAver molar is incom- 

 pletely formed. 



The carnivorous adaptation of teeth is next introduced, first 

 because it is simpler and more direct in its evolution than the 

 herbivorous modification and secondly because there is a direct 

 succession toward this adaptation in the family Dasyuridae to 

 which Phascologale belongs. 



Sarcophilus ursinus, the Tasmanian Devil, a purely carniv- 

 orous, powerfully built and very ferocious animal inhabiting 

 Tasmania alone, is becoming rapidly exterminated by the farm- 

 ers as the penalty of its depredations on the stock. This ugly 

 and nocturnal animal, illustrated in Fig. 19, kills every creature 

 which falls in its way and is not too large to attack: even 

 sheep are not infrequently victims of its bloodthirstiness. The 

 size of the skull is shown by the millimeter scale. The animal 

 is about as large as a terrier though much thicker set and with 

 shorter limbs. 



The tooth formula is: 



l|, Cj,p|,m|. total 42. 



