242 
PEOFESSOE OWEN ON THE FOSSIL MAMMALS OF AUSTEAL1A. 
it likewise is in Thylacoleo*). “If, therefore,” proceeds Dr. Falconer, “the function 
is to be deduced with such facile certainty from the mere form, the premolar of 
Hypsiprymnus ought also to be carnivorous. But we know that the genus is so strictly 
herbivorous that the family to which it belongs has been regarded as representing in 
the Marsupialia the Ruminants of the placental Mammals. With this fact before us, 
is it likely that the premolars of Plagiaulax and Thylacoleo ‘ were applied to cut and 
divide flesh’ V’f 
To this I reply ; consider the difference of the molar teeth following the trenchant 
one in Plagiaulax and Hypsiprymnus respectively, and the true solution will be given 
§ 14. Interrupted and continuous applications of Teeth. — The deduction of the 
carnivorous nature of the extinct Marsupials in question was drawn not from shape 
merely, but from correlation of teeth. The “ arbitrariness,” if such quality be predi- 
cable of the conclusion, is applicable to the guiding principle, not to the palaeontologist 
confiding therein. If reference to confirmatory and collateral facts was omitted in the 
Papers of 1859 and 1869, it was under the belief of their being the common property 
of the interpreters of fossil remains. 
In the adaptively modified dentition of the class Mammalia the differently shaped 
teeth are put, some to occasional and interrupted, others to continuous use. The 
incisors of the child biting a piece of bread and butter exemplify the first functional 
character ; the molars which pound the piece bitten off, the second. These incisors are 
trenchant or sharp-edged like the premolar of a Bettong or the carnassial of a Cat; 
their action in the human subject leaves a clean semicircular border of the bitten slice. 
The teeth, of whatever kind, incisors, premolars, or molars, which have the continuous 
work show its effects by an abraded surface. Those which have the occasional and in- 
terrupted work show little or no indication of such. The laniaries of Carnivora , when 
they have pierced and lacerated the prey, have done their work ; the gnawing off of the 
pieces of flesh adapted for the imperfect tubercular mastication and for deglutition is 
effected by continuous action of the sectorial blades, the mouth being turned sideways 
to the food, as may be seen in the Felines and other Carnivora which have the largest 
and best-shaped carnassial teeth. Such action and application of these teeth are exem- 
plified by the clean-worn, smooth, oblique surface sloping in the opposed blades down 
their opposite and opposed sides. 
The same functional character, relating, that is to say, to “ time” or “ prolongation of 
use,” is indicated by the incisors. Those in Thylacoleo and Plagiaulax show no evidence 
* XII. p. 310. “ The great cutting premolar of Thylacoleo bears no real comparison with the carnassial 
tooth of the Carnivora, hut with the compressed premolar of the Hypsiprymni.” — lb. p. 316. 
t X. p. 356 ; XI. p. 440. 
+ Dr. Falconer, indeed, does strengthen his attack by calling in the argument from correlation ; hut he selects 
a different tooth from that of the Cuvierian principle : — “ When this conclusion as to the herbivority of Plagi- 
aulax ” and Thylacoleo “ from similar trenchant characters of premolars with those of Hypsiprymnus is coupled 
with the obviously phytophagous type of the incisors, the conviction will he confirmed.” — X. p. 357 ; XI. p. 440. 
