PEOFESSOE OWEN ON THE EOSSIL MAMMALS OF AUSTEALIA. 
51 
The skull of Nototlierium is shorter in proportion to its breadth and depth than in 
Diprotodon, and differs in the singular way in which the maxillary or facial part is bent 
up upon the cranial part, exemplified in figure 1, Plate II., and by the angle, before 
noted, which the bony palate forms with the basis cranii. The shortness is mainly due 
to that of the antorbital extent of the skull ; the diastema between the incisors and mo- 
lars is relatively as well as absolutely less than in Diprotodon. The Notothere resembles 
the Koala (ib. fig. 3) and Wombat in the small proportion of the skull in advance of 
the orbits ; the Diprotodon is more like the Kangaroos in the length of this part. The 
terminal expanse and lateral tuberosities of the upper half of the bony nostril is a pecu- 
liarity of Nototlierium ; but it is instructive to note them in both Plmscolarctos and 
Phascolomys (Plate II. fig. 4) ; the fore part of the bony muzzle is expanded laterally 
by an outward swelling of the front border of the premaxillary (ib. 22 ) where it joins the 
nasal (ib. 15). 
In the form, especially breadth, of the external nostril the Notothere resembles the 
Wombat, while the Diprotodon is more like the Kangaroo in this respect; but no 
known existing Marsupial shows the septal plates developed from the premaxillaries at 
the entry of the nasal passages, as in both Nototlierium and Diprotodon. The Wombats 
make the nearest approach to this peculiarity. 
The Notothere surpasses the Diprotodon in both the absolute and relative size of the 
zygomatic arches. This difference is very striking when a front view of the cranium (as 
in figure 2 of Plate II.) is compared with the similar view given of the Diprotodon’s 
skull in Plate xxxv. fig. 2, in the Philosophical Transactions for 1870. 
This most extraordinary feature in the cranial organization of the present large ex- 
tinct Plerbivore leads me to submit the following remarks. 
The zygomatic arches are relatively stronger and wider in Proboscidians than in 
Ruminants and Solipeds ; they are widest and thickest in the bilophodont Dinotheres, 
the temporal fossae being of corresponding capacity. Still more developed are these 
arches in the Manatees, the Tapirs, and the bilophodont Megatheres, especially in 
the vertical extension of the bone giving attachment to masticatory muscles. It would 
seem that the working of opposed double-ridged grinders required greater strength 
and more direct horizontal pull of the masseteric muscular fibres than the working 
of the more complex but flatter molars of the Ox, Horse, Rhinoceros, or Elephant. 
The phytophagous Marsupials have the grinding-surface of their many massive molars 
raised into prismatic cones or transverse ridges, and their skull is remarkable for the 
great strength, size, and span of the zygomatic arches. The descending process from 
the fore and under part of the arch, for extending the origin of the premasseter muscle, 
adds to the zygomatic complexities and characterizes the Po ’epliaga among existing Mar- 
supials. This osteological feature is not found in any gyrencephalous Herbivore ; but it 
exists, with a different relation to the constituent bones of the arch, in the lissencephalous 
Sloths, Megatherioids, and Glyptodonts. In the Nototheres the zygomatic development 
reaches its maximum, with the dependent process extending from the maxillary element 
H 2 
