216 
PROFESSOR OWEN ON THE FOSSIL MAMMALS OF AUSTRALIA. 
the smooth and polished surface (Plate 28. fig. <5) presents an oval figure, the great end 
outward; the long diameter is 7-g- lines (15 milfims.), the short diameter, near the outer 
side of the worn surface, is 5^ lines (11 millims.). The enamel, nearly 2 millims. in 
thickness, is limited to the anterior surface, bending slightly hack at the outer and 
inner margins ; not more than 9 lines in length of the enamelled crown remains. The 
whole incisor, as usual, is curved lengthwise, with the greater convexity anterior ; the 
root contracts to its implanted end ; the length of the incisor, in a straight line, as here 
w 7 orn, is 1 inch 8 lines. The portion of cranium preserved, from the fore part of the 
front incisor to the back of the last molar, measures 6 inches 8 lines. About 2 inches 
of the facial part of the premaxillaries are preserved, bounding by a curved and obtuse 
border, thinning as it rises, the anterior nostril (Plate 28. fig. 1, 22 ). According to the 
proportions of some existing Wallabies, which retain the premolar with the last molar 
in use, 5 inches may be added for the extent of skull behind the last molar, and the total 
length of the skull in Sthenurus Brehus may be moderately estimated at 12 inches. 
The skull, so far as it is shown in the present specimen, has been crushed sideways, 
not partially as in the cave fossil, but by a pressure operating along a more extensive 
plane, and which I deem to be due to movement of the matrix, rather than to the jaws 
of a destroyer or devourer. 
The lower jaw, which appears to have been imbedded originally in connexion with 
the upper one, has suffered similar lateral compression. Only the fore part of the 
mandible, has been obtained or transmitted: it includes the pair of lower incisors with 
the premolar and two following molars of the right side ; these are much worn. The 
length of the diastema is 2 inches : in Sthenurus Atlas f it is 1 inch 3 lines. In the 
course of the pressure to which this mandible of Sthenurus BreJius has been subject, 
the attachment of the broad symphysis has been overcome, and the right ramus has 
been moved a little in advance of the left. 
The thin alveolar sheath does not extend to, or has been lost from, the end of the 
cement-clad root next the enamelled crown. This expands as it extends forward, and 
terminates in a polished worn surface, 10 lines in long diameter (obliquely transverse), 
5 lines in fore-and-aft diameter. The length of the enamelled (under or outer) part of 
the crown is 8 lines, that of the entire tooth is 2^ inches. The fang, as usual, tapers as 
it recedes in its socket (Plate 28. fig. 1, i*). The narrow symphysial border sinks from 
the premolar alveolus with a sharp curve before extending forward to expand upon the 
terminal part of the socket of the incisor. The outlet of the dental canal (v) is nearer 
the molars, and the diastema, with the symphysial part of the ramus, is longer, relatively, 
than in Sthenurus Atlas. 
A third example of the premaxillary part of the skull with the fore part of the right 
maxillary, of a still older individual of Sthenurus Brehus from Queensland deposits, 
shows the six incisors in situ , much worn, and the form and transverse extent of the 
palate between those teeth and the molars. The length of the diastema is 2 inches 
t Phil. Trans. 1874, plate xxii. fig. 5. 
