124 



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. The more extended anterior surface indicates that the lower carnassials 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 carnassials 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 working 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 impres- 

 sions, 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 Thylacoleo given at p. 111. The breadth of the palate 

 between the fore parts of the carnassials 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 carnassials 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 differential 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 Sdrcophilus" (p. 312). 

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

 about 3 lines in advance of the alveolus of that tooth (here the carnassial, p 10 lines 

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

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

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

 and 6 lines in short diameter. This difference indicates the minor extent of sensitive 

 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 XVII. 2). The lower ends of the condyles are about 5 lines apart, the 

 upper ends 1 inch 3 lines. The foramen magnum is 1 inch in transverse, and 1\ lines in 

 vertical diameter : it looks backward and a little downward. About 4 lines in advance 



