PROFESSOR OWEN ON THE FOSSIL MAMMALS OF AUSTRALIA. 
211 
fig. 2, Plate 25, and fig. 4, Plate 26) accord with the characters shown in more frag- 
mentary specimens of Sthenurus Atlas. Consequently can be added by means of the 
present fossil the characters of the first and third upper incisors to the previous know- 
ledge of the dentition of that large extinct species. 
The fossil evidence of this young individual of Sthenurus Atlas presents a condition 
which significantly points to the nature of its violent death, and to the operation of the 
powerful jaws and teeth of its carnivorous destroyer. 
The upper jaw, anterior to the orbits, has been nipped in by a cross bite ; another 
grip in a vertical or obliquely vertical direction in the orbital region has crushed the 
right half in the course of the interfrontal and internasal sutures to a lower level than 
the left half, with a similar degree of forward dislocation. The skull has been subject 
to this violence in its fresh state, and the matrix has subsequently become petrified 
about it, and has preserved the dislocations. 
If they had been due to movements of the matrix after fossilization, the petrified 
head would show fracture corresponding to the bone; but no such evidence of post- 
humous crushing of matrix and fossil being present, I presume that the skull, if it 
had been imbedded uninjured, would have retained its form when petrified, and con- 
clude that the actual state of the fossil was that in which it was interred before 
petrifaction began. 
The anterior incisor (Plate 25. fig. 2, i i) is curved, as in most existing Kangaroos ; 
but besides its superiority of size to that in the largest kind, as shown by the breadth 
of the crown*, the exserted and enamelled portion is both absolutely and relatively 
longer, and thus makes a nearer approach to the character of the first upper incisor in 
Diprotodonf. The convex or fore surface of the crown of i i in Sthenurus Atlas is 
traversed longitudinally by a shallow and rather wide groove behind the mid line of 
that surface, which groove deepens near the cutting-edge, and thus marks it with a 
feeble notch. The enamel also shows some fine longitudinal striations. This wrap of 
the tooth is uninterrupted, but becomes much thinner at the back part. A transverse 
section of the crown would give a long, narrow oval, rather broader at the outer and 
hinder end. 
The breadth of the tooth, or length of the oval, is 10 millims., or 4f lines ; the 
thickness or antero-posterior extent is 4 millims., or 2J lines. The hind margin of the 
tooth, near the cutting-edge, shows the shallow indent caused by the crown of the 
second incisor ; but this tooth in both premaxillaries has been displaced by the lateral 
crushing of these bones in the recent state, and was probably lost prior to the imbedding 
of the skull. The second incisor is the smallest and least deeply implanted in most 
Kangaroos. 
The third incisor (Plate 25. fig. 2, i s) had not been fully developed ; its crown had 
only partially emerged from the socket, whence its preservation. It is in the form of a 
* Compare with. Phil. Trans. 1874, plate xx. fig. 17 ( Macropus major). 
t Phil. Trans. 1870, plate xxxv. fig. 1, i l. 
2 G 
MDCCCLXXVI. 
