PROFESSOR OWEN ON THE FOSSIL MAMMALS OF AUSTRALIA. 
795 
The inner side of the tooth is flatter, and is impressed at its middle third by three shallow 
parallel grooves descending rather obliquely backward. The coronal ends of these 
grooves give a crenate character to that part of the enamel. A field of dentine is exposed 
on the broader hind lobe. 
The crown of the second molar (Plate LXXX. figs. 6 & 7, d 3) has the two transverse 
lobes and a prebasal production ; a continuous tract of dentine is exposed on these parts 
and along the mid link connecting the two lobes. Certain longitudinal impressions on 
the outer surface of the crown give a wavy character to parts of the peripheral coat of 
enamel on the working-surface of the tooth. 
The third molar ( d 4) is mutilated by fracture in both rami, but least so in the right. 
The prebasal ridge is narrow transversely in proportion to its length ; its enamel coat 
is indented ; the fore limb is feebly indicated. The hind surface of the hind lobe shows 
three vertical enamel ridges, two of which attain the grinding-surface. The mid link 
is strengthened by a vertical ridge on its inner side. 
In the fourth molar (m 1) the prebasal ridge has a distinct link passing from its outer 
angle toward the middle of the fore part of the front lobe, ending nearer the outer side. 
Short ridges project from this surface on the inner side, marked off by the fore link. 
The mid link passes from near the outer side of the fore lobe to near the middle of the 
hind lobe. The link is complicated by a vertical ridge or fold of enamel on its inner 
surface. Similar ridges mark the inner half of the fore surface of the hind lobe. On 
the hind surface of this lobe, internal to the ridge by which the outer convex end there 
terminates, is a narrow pyramidal tract of enamel in low relief, the apex of which reaches 
the working-ridge of that lobe ; internal to this pyramid is a second, less strongly defined 
by two sharp linear grooves. The inner side or end of each transverse lobe is narrower. 
The fresh and unworn crown of the penultimate molar ( m 2) shows well the accessory 
ridges which complicate the enamel cap of its crown. In this tooth, as in m 1, the pre- 
basal ridge beginning near the base of the inner end of the fore lobe curves forward and 
outward, rising rapidly to a narrow summit, which seems to represent a third short trans- 
verse lobe ; this, as soon as it has received or sent off the fore link, subsides suddenly 
upon the base of the fore lobe before attaining its outer end. 
The position of the germ of the last molar is such that the transverse lobes turn 
their working-edges obliquely inward, rather forward, and, with but a very slight incli- 
nation, upward, indicating the semirotating movement by which, in the course of the 
growth of both tooth and jaw, the crown is brought into the latter direction, and in a 
working line with the antecedent grinders. The superadded complexities noted in these 
teeth are multiplied in the last molar ; at least so much of the hind surface of the hind 
lobe as is formed shows, in the left ramus, not fewer than six accessory ridges in the 
flattened and rather depressed tract included between the hinder terminal ridges or 
angles of the outer and inner convex ends of the hind lobe. Of these six vertical ridges 
two are larger than the rest, and of the narrow pyramidal shape before mentioned (they 
answer to those marked h in fig. 10, Plate LXXIX.). 
