PEOFESSOR OWEN ON THE FOSSIL MAMMALS OF AUSTRALIA. 
47 
figs. 2 & 3), then bend abruptly downward and arch transversely inward to abut against 
the middle third of the alveolar plates of the maxillaries, a thick transversely extended 
process (Plate II. figs. 1 & 2, sc) being continued downward from the angle of the inward 
curvature. From the hinder origin or “ pier ”(27) each arch gains, as it advances, a vertical 
extent of 4 inches 3 lines ; then contracts to one of 3 inches, again expanding slightly 
in the vertical direction, and greatly in the transverse one, before the inward twist to 
form the maxillary pier or abutment. The inner surface of the arch is smooth and 
slightly concave ; the outer surface is rough, convex, and outswells into two large pro- 
tuberances, one at the part (e) anterior to that supporting the joint for the lower jaw, 
the other and larger (fig. 2 ,f) at the angle formed by the down-bending of the arch to 
the orbital floor ; the latter is most prominent and best defined. The floor of the orbit 
(ib. fig. 1, r) is of comparatively small extent, limited to the inner or mesial half of the 
inwardly bent part of the zygoma, of a triangular form, indicative, with the inner orbital 
concavity leading to the antorbital process ( 5 ), of the small relative size and low position 
of the eyeball ; with this position the foramen opticum corresponds. The extent of the 
anterior inwardly bent part of the zygoma is 5 inches. From the lower angle of the 
bend is continued downward the process ( 2 c) for an extent of 3 inches, with a twist, making 
its sides look forward and backward, its borders outward and inward. Its breadth is 24 
inches, its termination subtruncate ; from its inner border to the alveolar part of the 
maxillary, between the penultimate and antepenultimate molars, is 3 inches 6 lines, 
giving the span of the arch extending transversely from the anterior root of the zygoma 
to the masseteric process, the end of which reaches below the level of the upper grinding- 
teeth (Plate II. fig. 1, 21 '). The anterior root of the zygoma is three-sided: one, the 
upper horizontal surface, forming the floor of the orbit, has a fore-and-aft extent of 2 
inches ; the anterior and posterior surfaces converge to a thick lower border, which is 
above the interval between m 1 and m 2 , terminating about 10 lines above the outlets of 
the sockets of those teeth. The antorbital foramen (ib. 21 ) is vertically elliptic, 10 lines 
in long and 6 in short diameter, situated 1 inch 9 lines in advance of the orbit, and about 
2 inches above the outlet of the anterior molar (d 3). The antero-posterior extent of the 
maxillary alveoli, in a straight line, is 7 inches ; their outlets describe a gentle convexity 
downward as well as outward, the right and left series diverging from the anterior pair 
to the fourth and incurving slightly at the last pair (Plate III. fig. 3, d 3 , m 3 ). The 
outer roots of the contained molars cause corresponding prominences of the sockets, 
giving an undulatory surface to that part of the upper jaw (Plate II. fig. 1). This 
extends, perhaps in conjunction with the palatine bone, about an inch beyond the last 
molar, with an upward slope. 
The breadth of the hind part of the palate here is 3 inches 3 lines. The posterior 
nares form a triangular aperture, with the base above the palate, 2 inches 3 lines broad, 
thence contracting as it extends obliquely upward and backward to a point at the, fore 
end of the basisphenoid ridge ; the length of the aperture from this point is 4 inches 
6 lines. The aperture is bounded laterally by the pterygoid plates. 
