54 
PROFESSOR OWEN ON THE FOSSIL MAMMALS OF AUSTRALIA. 
outsides of these, from the cavities (Plate III. fig. 3, g , 27) receiving them, to have been 
1 foot, or thereabouts. 
The outer surface of the horizontal ramus (Plate II. fig. 1, 32, q) is smooth, very convex 
vertically where it advances from the ascending ramus, but rising with a slight con- 
cavity to the outlets of the sockets; the convexity subsides as the jaw advances and the 
surface ascends more vertically to the outlets of the three anterior molars (ib. d 3, d 4, 
m 1 ), but it continues the vertically convex curve to the lower border. The thickness 
of the ramus before inbending to the symphysis is 2 inches ; its height where it joins its 
fellow at s (Plate IV". fig. 2) is 3 inches 5 lines. At the lower and back part of the 
symphysis is a transverse roughish crescentic depression (Plate IV. fig. 3, v) for muscular 
insertion. The general longitudinal lay of the outer surface of the horizontal ramus 
is a feeble convexity forwards as far as below the second molar (d 1 4 ), where it begins 
to change to a concavity leading on to the symphysial part (fig. 1 , 32-k), containing, 
anteriorly, the sockets of the incisors. On the vertical parallel of the fore part of the 
first molar socket, about halfway between the upper and lower borders of that part of the 
ramus, is an outlet of the dental canal (ib. 32) ; it is subcircular, 5 lines in long diameter. 
The inner surface of the horizontal ramus (Plate IV. figs. 1 & 2,i) sinks sheer below 
the outlets of the last socket, and with a slight vertical convexity from that of the penul- 
timate molar ; it is at first feebly concave, then convex to the back part of the symphysis, 
and the surface is uniformly concave at the upper part of the symphysis (ib. fig. 2, s*), 
between the three anterior sockets of the right and left sides. The longitudinal lay of 
the inner wall of the ramus is feebly convex posteriorly, changing to a concavity deep- 
ening into the back and upper part of the symphysis. This junction of the right and 
left rami is completely ossified without a trace of the primitive separation shown in 
Plate VI. figs. 2, 3, 4, s, s', s * ; herein contrasting strongly with the condition of the 
joint in the Kangaroo f. 
The hind surface of the symphysis (Plate IV. figs. 2 & 3, s), vertically convex and 
smooth, is on the vertical parallel with the back lobe of third molar (m 1 ), near, but not 
quite extending, to the interspace between its socket and that of the fourth molar (m 2). 
The upper surface of the symphysis (ib. fig. 2, s*, s) between the three anterior molars 
(>?i 1 , d 4, d 3 ) is a rather deep smooth longitudinal canal, the margins of which begin to 
be encroached on by a diastemal ridge (ib. k), continued forward from the socket of d 3 
with a slight curve convex inward. 
The antero-posterior extent of the five molar alveoli is 7 inches 5 lines. The breadth 
of the anterior division of the first socket is 3^ lines, of the posterior division 5 lines ; 
the depth is shown in the jaw of the young Nototherium (Plate VI. fig. 5, l). The 
sockets of the other molars increase in breadth to the anterior division of the last, which 
is 1 inch 1 line across. The alveolar plate rises in an angular form at the intervals of 
the sockets, and at those of the diverging roots of each tooth on both outer and inner 
sides of the jaw. 
f Owejt, Osteology of the Marsupialia, ‘Anatomy of Vertebrates,’ vol. ii. p. 350. 
