PEOFESSOB OWEN ON THE FOSSIL MAMMALS OF AUSTEAL1A. 
225 
No. 29 of the series, is a smaller portion of the fore part of a right ramus, with the 
entire incisor, the carnassial, and first molar in situ. The whole length of the base of 
the incisor is exposed, and the obtuse termination of the closed and contracted end 
of the root (Plate XIII. fig. 2). The fractured state of the bone also shows portions of 
the fore and hind roots of the carnassial (p> 4 ), the latter apparently the larger, contrary 
to that in the lower carnassial of Felines, which is not the homologous tooth, although 
with a similar adaptive modification of crown. The length of the incisor is 3 inches 
3 lines, that of the enamelled crown appears to be about 1 inch 8 lines ; the antero- 
posterior breadth of its base is 9 lines. The position, direction, and curvature of the 
incisor in this specimen accord with those in the photograph copied in fig. 1, 
Plate XIII., and with the restoration based on the direction of the empty socket in 
the subject of Plate iv. fig. 6, Philosophical Transactions, 18G6. The vertical extent 
of the fore part of the carnassial (p> 4 ) is 1 inch 9 lines, that of the enamelled crown 
being 7-| lines. 
All the evidences yielded by the specimen (figs. 1-3, Plate XII.), by the casts (Plate xi. 
fig. 3, Phil. Trans. 1859), and by the photographs (Plate XIII. figs. 1 & 2, jp 4) concur in 
showing the closer resemblance of this sectorial tooth to the carnassial of the large pla- 
cental Carnivores (Plate XII. figs. 9 & 12) than to the sectorial premolar in Pat-Kan- 
garoos (ib. figs. 8 & 10). The crown of the tooth (fig. 11) is bent lengthwise, with the 
convexity outward, the concavity inward ; and this is chiefly at the hinder half of the 
tooth (fig. 3, p> 4 ). The fore part of the crown is the thickest, and that by the promi- 
nence of the inner surface at the anterior fourth, which makes a low obtuse ridge (r, fig. 11, 
Plate XII.) divided by a depression or channel from the anterior ridge (a) or border of 
the crown, which represents the prebasal ridge (a) in the carnassial of the Hyaena (fig. 12). 
The broader part of the trenchant surface ( b , fig. 11) is anterior, as in Hyaena (It, fig. 12). 
The trenchant margin does not extend in a straight line, but is subconcave, though less 
so and more continuously than in Hyaena. The effect of these curves of the cutting part 
of the blades in Thylacoleo, as in Felts and Hyaena , is to make them meet at successive 
parts in the act of cutting, not by simultaneous opposition of the entire cutting-edges of 
the opposed blades. The vertical undulation of the enamel is finer, less marked, in the 
lower than in the upper carnassials, and is confined to the basal part of the inner surface, 
not to the apical half of the crown as in Ilypsiprymnus (fig. 10). 
In the cast of a specimen of a right mandibular ramus with the carnassial less worn 
than in the specimen Plate XII. figs. 1-3, the abraded surface is interrupted midway, 
indicating a bilobed character of the unworn margin, as in the lower carnassial of Felines ; 
the abraded surface in the cast expands from the unworn part of the dividing notch 
forward toward the anterior end of the tooth and backward to the posterior end (Plate 
XII. fig. 11). The subject of figure 6, Plate XII., is a specimen worked out of the 
breccia transmitted by the Trustees of the Australian Museum, and shows the propor- 
tions of the two roots ofp 4, lower jaw. 
