104 ON AN EXTINCT MAMMAL ; 
only necessary to ascertain to which of the older and better known 
genera it has the nearest alliance. The absence of the dilated 
muzzle, flat face, elevated forehead, huge zygomata, and strongly 
inflected mandibular angle of Nototherium shews that in its leading 
characters its affinity to that genus was anything but close. From 
Diprotodon it was not so far removed ; in the several features in 
which it departs from Nototherium, it approaches—or rather 
departs—less from its more ponderous contemporary. In the con- 
formation of the posterior moiety of the mandible, that of the 
condyle excepted, it indeed resembles Diprotodon rather closely ; 
the position of the dental foramen in the two is almost identical, 
and the chief difference is the relatively greater development of 
the alar expansion in the newer genus. 
The position of the surfaces of wear of the incisors being on 
the same (inner) side of the opposite pairs, it is plain that they 
cannot have resulted from the mutual attrition of the corresponding 
teeth—in fact, a cropping or gnawing function was impossible in 
teeth so formed and placed as these are. It seems probable there- 
fore, that the vertical action of the jaws was greatly subordinate to 
their horizontal motion, unless these surfaces were worn by some 
use of the teeth (other than prehension), preliminary to the act of 
mastication, in other words, if they are due to mutual contact 
during that act it follows from the length and distance apart of the 
tips of the teeth that the reduction of the food could only be 
effected by a strong transverse, combined with a by no means 
feeble vertical action of the jaws. Such a recurvilinear motion is 
of course only an exaggeration of usual masticatory movements— 
an exaggeration conditioned by fodder unusually coarse in quality, 
and perhaps copious in quantity. It is, however, to be observed 
that the inference is, to some extent, modified by the structure of 
the joint between the upper and lower jaws. The extent and 
form of the articulatory surface of the condyle do not suggest any 
great range of rotular motion, and all retraction of the jaw is 
prevented by the concavity of the glenoid surface, and the extent 
and depth of the post-glenoid process. But the close locking of 
the jaws does not seem incompatible with laborious grinding, and 
certainly the effects of such grinding are evident in the degraded 
state of the molars; these have the semblance of age to a far 
greater degree than the anterior teeth. Seeing that the tusk-like 
incisors were not, or were only to a very limited extent, cutting 
teeth, and that the food to be utilised was voluminous and harsh, 
it does not seem too speculative to imagine that the chief use of 
the front teeth was to aid the lips and tongue in feeding, initiating 
