263 



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 Liprotodon ; 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 XXXIX., k, 'i), 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 

 transversely 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 

 surface, including the roots of the incisors (Plate XXXIX. 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 Ci). 



At the upper part of the symphysis the ridge (fig. 3, k), of which the beginning or 

 hind part was noted in the description of the preceding specimen (Plate XXXVIII. 

 figs. 1 & 4, k\ is here seen to converge toward its fellow for the extent of an inch, then 

 to be continued straight forward, broadening and subsiding. The pair of ridges form 

 the sides of the smooth channel (s*), grooving the upper surface of the symphysis, and 

 f Sec Plate XXVI. fig. 2, s, where the same form of incisive alveolar outlet is shown in the mandible. 



