74 PROFESSOE OWEN ON THE FOSSIL MAMMALS OF AUSTRALIA. 



outer surface. The hindmost part of the worn surface, which is 4 lines across, slopes 

 rather outwardly from the rest, at a low angle defined by a linear boundary. I conclude 

 that this surface is formed by the attrition of the small tooth succeeding the carnassial 

 in the lower jaw, and marked m 1, fig. 3, Plate XI. of the former paper. The more 

 extended anterior surface indicates that the lower camassials pass within the upper ones 

 when the mouth is shut. The whole abraded surface shows a play of the teeth for 

 trenchant action, like that of the blades of shears, in a more striking degree than in the 

 camassials of Felines. The fore part of the carnassial, here 7 lines in breadth at the 

 base of the crown, is formed by a ridge of enamel, acquiring, as it approaches the work- 

 ing surface, a line in breadth; from this the crown quickly expands to its greatest 

 breadth, which is defined by a similar vertical ridge on both the outer and inner sides of 

 the tooth. The enamel tract between the anterior and outer ridges is convex ; that 

 between the anterior and inner ridges is flat. The outer surface of the enamel behind 

 the ridge shows several slight linear vertical impressions, between which the enamel 

 slightly bulges out, at the basal part of the crown, the grooves subsiding halfway 

 toward the trenchant border ; the enamel is also finely wrinkled. The vertical extent 

 of the enamel decreases from the fore to the hind end of the crown. I have nothing 

 more to add from this second specimen to the description of the upper carnassial of 

 Tliylacoleo given at p. 311 of my former paper. The breadth of the palate between 

 the fore parts of the camassials is 3 inches 5 lines, and between the hind parts 3 inches 

 10 lines ; showing the slight convergence of the antero-posteriorly extended crowns of the 

 camassials anteriorly. 



In the portion of upper jaw first described, the fore part had been broken away 

 immediately in front of the alveolus of the carnassial tooth ; but enough of the bone 

 on the outer side of the socket remained to determine a difierential character between 

 Felis and Thylacoleo in favour of the marsupiality of the latter. From the state of the 

 first specimen I could only say that the suborbital or antorbital canal " must open some 

 way in advance of the socket of the penultimate tooth, as it does in Sarcophilus" (p. 312). 

 The present specimen shows that the anterior opening of the canal (Plate III. 21) is 

 about 3 lines in advance of the alveolus of that tooth (here the carnassial, j? 4), 10 lines 

 above the alveolar border of the maxillary, and 6 lines behind the maxillo-premaxillary 

 suture. The foramen is vertically elliptical, 3J lines in long diameter, and 2^ in the 

 opposite diameter. The corresponding foramen in Felis Leo may be 10 lines in long dia- 

 meter and 6 lines in short diameter. This difference indicates the minor extent of sensi- 

 tive surface and (vibrissal \) appendages in Thylacoleo as compared with Felis, and corre- 

 sponds with the singular relative shortness of the muzzle in Thylacoleo, which the pre- 

 sent instructive fossil exemplifies. 



In this specimen the right occipital condyle is entire : it forms outwardly a strong 

 oblique convexity, broadest above, contracting as it bends round the outside of the fora- 

 men magnum forward and inward ; toward the foramen the condyle is slightly concave 

 lengthwise (Plate III. 2). The lower ends of the condyles are about 5 lines apart, the 



