173 



are those correspondences in the upper carnassial, and are unmistakable. A broader 

 well-defined prominence on the fore part of the inner surface of the crown of the lower 

 sectorial (Plate VIII. fig. 11, r) leaves a part anterior to it (ib. a) representing the anterior 

 basal talon, chiefly marked or extended upon the inner surface of the fore part of the 

 crown in the lower carnassial of Felis and Hycena. The indications of vertical elevations 

 of enamel are more feeble in the lower than in the upper sectorial, and are chiefly seen 

 at the basal part of the inner surface. The notch at the middle of the trenchant border 

 in the less worn lower carnassial (Plate VIII. fig. 11) clearly indicates divisions resem- 

 bling, though more feebly marked, the anterior and posterior lobes of the homologous 

 tooth in the placental Carnivora (ib. fig. 12). 



The absence of the anterior transverse expansion, and the straight line described by 

 the trenchant border, in the lower sectorial of the Potoroos, is, at least, as strongly marked 

 in the lower jaw (ib. figs. 8, 10, 13) as in the upper one (Plate VII. figs. 17, 18). In 

 juxtaposing the specimens of the homologous teeth in Thylacoleo and any Potoroo for a 

 true deduction of comparative similarity and difference, " one sees at once that the great 

 cutting premolar of the Hypsiprymni or Rat-Kangaroos is" not "a miniature of that of 

 Thylacoleo"*. And, if it were, the function of such sectorial could not be deduced from 

 mere shape, but from the nature of the other teeth wherewith it is associated, and the 

 modifications of the jaws by which such dentition was worked. 



The varieties of form above defined, inasmuch as they modify the surface of a carnas- 

 sial tooth, may be said to be ' merely superficial ;' but I am at a loss to know how that 

 disparaging epithet affects the question. Professor Flower offers no testimony of a 

 'deep-seated' structure common to the sectorials in Poephaga and Paucidentata, and 

 different from those in placental Carnivora. He mil find one if he examines microsco- 

 pical sections of the teeth in question f. But it is one which Thylacoleo shows in com- 

 mon with Thylacinus and Sarcophilus, and it is a marsupial modification, not a macro- 

 podal one. 



The student in reading of the " great cutting premolar of the Rat-Kangaroos" must 

 bear in mind that the epithet is relative. Where such tooth is greatest in those vegeta- 

 rians it is small in comparison with its homologue in Thylacoleo. The difference of 

 shape, direction, term of growth, and of every character meaning function is still greater 

 and more obvious in the incisors of the Diprotodonts compared than in the sectorials ; 

 and the degree and kind of difference shown by Thylacoleo testifies to the carnassiality 

 of the main representative tooth of the molary series. 



Against the association of that great carnivore with the Poephaga "(= Macropoda, 

 V. d. H.)," there are opposed not only the differences above demonstrated in the homo- 

 logous sectorial teeth, but the absence of the third pair of upper incisors and the pre- 

 sence of premolars in advance of the sectorial one in both jaws of Thylacoleo. It will 



* XII. p. 310. 



t It is that represented in Plate 102 of my ' Odontography,' showing the extension of dentinal tubules into 

 the enamel. 



9 



