524 
PROFESSOR OWEN ON THE FOSSIL MAMMALS OF AUSTRALIA. 
mination of the nasals rather exceeds that of the cranial part at the parietal region ; it 
is also greater than the beginning of the facial part of the skull in advance of the orbits 
and molar alveoli, whence there is a gain both in depth and breadth as it approaches 
the anterior terminations ; but the uniformity of this diameter of the skull along the 
medial line, from the superoccipital forward to the premaxillo-nasal part, viewed side- 
ways or in direct profile, is a remarkable characteristic of Diprotodon. 
The part of the maxillary (Plate XXXV. fig. 1, 21 ) lodging the molar series of teeth 
(d 3 -m 3) breaks the lower line of the profile, descending below it along the middle third 
of the length of the skull. The zygomatic arch is deep, long, but proportionally less con- 
vex outwardly, or less expanded, than in Tliylacoleo. Its base (ib. figs. 1 & 3, 27) seems as 
if continued from the whole side of the occipital plane, contracting rapidly at the upper 
border as the arch sweeps outward and forward ; the superoccipital crest being continued 
into the upper border of the arch, and this apparently without break or abrupt rise in 
any part of that border*. The frame of the orifice of the “meatus auditorius” (ib. 
% 1, 2 s) projects downward from the hind part of the lower border of the base of the 
zygoma, indicative of the tympanic. Immediately in front of this descends the postglenoid 
process (a) of the squamosal, and in advance of this is a second downward projection or 
convexity due to the “ eminentia articularis ” ( b ), which is here, as in Marsupials, a process 
of the malar ( 26 ). From this part the lower border of the zygoma runs forward nearly 
parallel to the upper one, but with a slight concavity, as far as the maxillary element of 
the zygoma, which sends down a strong, moderately long, obtuse, subcompressed masse- 
teric process (ib. 21 ') — a cranial feature which is peculiar to herbivorous Marsupialsf. 
The orbit (ib. fig. 1, r) is a relatively small vertically oval cavity, communicating 
widely behind with the temporal fossa (ib. 7 ). The external nostril (ib. figs. 1 & 2, n) 
is terminal, subvertical, rather expanded, and divided in great part by an upward exten- 
sion of the medial nasal plate of each premaxillary (ib. figs. 1 & 2 , 22 '), which plates, 
being in close contact, form the lower part of a long “ septum narium” at the outlet of 
the nasal cavity, recalling its condition in the extinct Rhinoceros tichorhinus. There 
is a narrow and short descending ridge at the coadapted medial borders of the nasals, 
wPich seems to have been continued into the septum by cartilage rather than by bone. 
I have alluded to the analogy which the structure of the external nostrils in I)iprotodo7i 
suggest to those of an extinct Pachyderm, but the truer and closer resemblance is found 
in the Marsupial group. The cavity of the nose is divided by a complete bony septum 
to within one-fourth of the outer opening in Macropus and Phascolomys$, advancing, in 
one species of Wombat, as in Not other ium, nearer to that outlet. 
* Some mutilation of the hind part of this upper border in both zygomata begets reserve in definitely pro- 
nouncing as to its normal outline. 
•h The descending masseteric process in Glyptodonts, Sloths, and Megatherioids is formed by the malar bone 
exclusively. Owen - , ‘ Anatomy of Vertebrates,’ vol. ii. p. 405, figs. 273, 274, 26, a. 
+ “ On the Osteology of the Marsupialia,” Zoological Transactions, vol. ii. p. 391. Anatomy of Vertebrates, 
vol. ii. p. 348. 
