PROFESSOR OWEN ON THE FOSSIL MAMMALS OF AUSTRALIA. 
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At the fractured part of the symphysis are parts of the bottoms of a pair of incisive 
alveoli ; that on the left side gives a transverse breadth of 9 lines and a vertical one of 
about 1 inch ; but the lower wall is broken away from the base. A still smaller por- 
tion is preserved on the right side. 
The indications suffice to show that the incisors were not developed as tusks, of size and 
proportions fitted for offensive or defensive purposes, as in Diprotodon ; their base and 
socket not extending backward beneath any of the molar alveoli, at least in the adult. 
Not more than an inch and a half of the toothless part of the symphysial end of the 
lower jaw has been preserved in the present specimen, and that only on one (the left) 
side. 
Accepting the evidence from size and proportion in the preserved parts of the present 
mandible and its dentition, in proof of its appertaining to a full-grown individual of the 
same species as the skull above described, the length of the part of the lower jaw with 
its incisors, in advance of the molar series, can be estimated and restored from that of 
the premaxillary and its incisors anterior to the molar teeth in the upper jaw. This 
estimate gives from the fore part of the anterior molar socket of the mandible to the 
tips of the pair of lower incisors an extent of at least four inches and a half. 
Complete as is this lower jaw compared with previously received specimens, including 
the one originally described, the relative extents of the sockets and protruded parts of 
the lower incisors would have remained to be determined. 
Fortunately a mutilated mandible, but with the symphysial end nearly if not quite 
entire, has been received by the Trustees of the Australian Museum, Sydney, and a plaster 
cast of this specimen has been prepared and transmitted, with their characteristic libe- 
rality and promptitude, to the Trustees of the British Museum. 
In this specimen an extent of the jaw forming the sockets of the pair of incisors 
(Plate V., Jc, 1), 2 inches 6 lines anterior to the first molar (ib. fig. 3, d 3 & s*), has been 
preserved ; but at this distance, the incisors with, perhaps, some small part of the fore 
part of their sockets have been broken off. The symphysis dwindles vertically and trans- 
versely to the condition of mere sheaths of the two approximate teeth, such sheath in 
no part of the fractured surface exceeding three lines in thickness, and where the bone 
comes nearest to the fracture it thins off to a fine edge (ib. fig. 4). As far as a cast can be 
trusted, part of the natural outlet of the sockets is shown below the teeth (ib. fig. 2, s'), 
the alveolar wall having extended further forward at their upper partf. 
The vertical diameter of the fractured or partially fractured end of the symphysis at 
the mid line is 1 inch 6 lines ; the transverse diameter is the same. The broken sur- 
face, including the roots of the incisors (Plate V. fig. 4, nat. size), is of a subquadrate 
form, with a mesial groove above (s') and a slighter one below. 
The lower contour of the mandible is continued, without interruption, but with gra- 
dual loss of convexity, from the inflected border (fig. 1, d) to the outlet of the incisors ( i ). 
f See “ Memoir on Diprotoclon Philosophical Transactions, 1870, Plate xli. tig, 2, s, where the same form 
of incisive alveolar outlet is shown in the mandible. 
