1868.] FLOWEK THYLACOLEO. 317 



vious : the points of ijenetration are doubled, the grasp is strengthened 

 by widening the base, and the dilacerating and killing powers are 

 multiplied. To arrange them collaterally in the axis would be to 

 place them at a disadvantage to the end to be attained. But when 

 a gnawing power is required, the middle incisors are powerfully 

 developed, and placed collaterally in the axis of the jaws, one on 

 each side, above and below, as typically exemplified in the placental 

 llodents and Chiromys. Doubtless a Rat, when seized, can inflict a 

 smart wound on the hand ; but the power is a secondary attribute, 

 complementary to the main function. Regarded in this aspect, it is 

 negatively stamped upon the incisors of Plagiaulax by their colla- 

 teral position that they are not constructed upon the carnivorous 

 plan of design, nor in rational correlation therewith" (op. cit. p. 352). 



It is certainly one of the most significant circumstances con- 

 nected with the relation of dental armature to food and habits, that 

 every known true predaceous carnivoi'ous animal (by which I mean 

 one which kills and eats creatures at all comparable to itself in bulk 

 and capable of making any effectual resistance) has powerful and 

 pointed canine teeth in both jaws, combined with comparatively 

 small incisors, which diminish in size as they approach the middle 

 line (see fig. 5, p. 313. A typical placental carnivore, as Felts, would 

 have exemplified this even more strongly) ; and, moreover, this 

 adaptive type of dentition is found equally well marked in animals 

 having similar habits, both in the placental and implacental series, 

 which differ so entirely in the far more fundamental or deep-seated 

 conditions of organization, including the characters of dental develop- 

 ment and succession*. This relation of canines to incisors is 

 evidently more especially related to the predaceous mode of life 

 than the characters of the molars. The compressed trenchant 

 form of the crown of the carnassial tooth, for example, is a special 

 peculiarity of the Cats and a few allied forms, and is not met with 

 in any of the carnivorous Marsupials. 



Now, to the above-described type of dentition, common to pla- 

 cental and marsupial carnivores, Tliylacoleo presents no sort of an 

 approximation : its lower canines are absent, its upper ones rudi- 

 mentary and probably functionless ; its central incisors in both jaws 

 were greatly developed. If such a dental machinery is of the most 

 effective type for predatory life, Lions, Tigers, Hyaenas, Wolves, 

 Dasyures and Thylacines must all be ill-fitted for the part they have 

 to play in nature's great arena. 



There is certainly one group of flesh-eating animals, the Shrews 

 and Hedgehogs, in which the type of dentition characteristic of the 

 true carnivora is widely departed from, the development of the 

 anterior incisors taking place at the expense of the lateral incisors 

 and canines ; but the living prey of all these animals is comparatively 

 small, feeble, and unresisting. They cannot on account of their 

 habits any more than their structure be regarded as typically car- 

 nivorous : the modics operandi of the Hedgehog in snapping up and 



* See Phil. Trans. 1867, part 2, p. 631, " On the Development and Succession 

 of the teeth in the Marsupialia." 



