OF THE MARSUPIALIA. 381 
The zygomatic arches are, however, complete in these, as well as in all the other 
genera ; and are usually, indeed, strongly developed ; but their variations do not indi- 
cate the nature of the food so clearly, or correspond with the differences of animal and 
vegetable diet in the same degree as in the placental Mammalia. No marsupial animal, 
for example, is devoid of incisors in the upper jaw, like the ordinary Ruminants of the 
placental series ; and the more complete dental apparatus with which the herbivorous 
Kangaroos, Potoroos, Phalangers, &c., are provided, and which appears to be in relation 
to the scantier pasturage and the dry and rigid character of the herbage or foliage on 
which they browse, require a strong apparatus of bone and muscle for the action of the 
jaws, and the exercise of the terminal teeth. There are, however, sufficiently marked 
differences in this part of the marsupial skull; and the weakest zygomatic arches are 
those of the insectivorous Perameles' and Acrobates, in which structure we may discern 
a correspondence with the edentate Anteaters of the placental series. Still the difference 
of development is greatly in favour of the marsupial Insectivora. The Hypsiprymni are 
next in the order of development of the zygomatic arches, which again are proportion- 
ally much stronger in the true Kangaroos. The length of the zygomata in relation to 
the entire skull, is greatest in the Koala* and Wombat’. In the former animal they are 
remarkable for their depth, longitudinal extent, and straight and parallel course. In 
the latter they have a considerable curve outwards, so as greatly to diminish the resem- 
blance which otherwise exists in the form of the skull between the Wombat and the 
herbivorous Rodentia of the placental series, as e. g., the Viscaccia. 
In the carnivorous Marsupials the outward curve of the zygomatic arch (which is 
greatest in the Thylacine and Ursine Dasyure*) is also accompanied by a slight curve 
upwards ; but this curvature is chiefly expressed by the concavity of the lower margin of 
the zygoma, and is by no means so well marked as in the placental Carnivora. It is re- 
markable that this upward curvature is greater in the slender zygomata of the Perameles 
than in the stronger zygomata of the Dasyures and Opossums. In the Koala and Pha- 
langers there is also a slight tendency to the upward curvature. In the Wombat the 
outwardly-expanded arch is perfectly horizontal. In the Kangaroo the lower margin of 
the zygoma describes a slightly undulating curve, the middle part of which is convex 
downwards. 
In many of the Marsupiata, as the Kangaroo, the Koala, the Phalangers, and the 
Opossums, the superior margin of the zygoma begins immediately to rise above the 
posterior origin of the arch. In the Wombat an external ridge of bone commences at 
the middle of the Jower margin of the zygoma, and gradually extends outwards as it 
advances forwards, and, being joined by the upper margin of the zygoma, forms the 
lower boundary of the orbit, and ultimately curves downwards in front of the ant-orbital 
foramen, below which it bifurcates, and is lost. This ridge results, as it were, from the 
1 Pl. LXXI, fig. 1. ® Pl. LXIX. figg. 1—3. ’ PI. LXXI. fig. 6. * PL. LXX., figg. 1 & 5. 
