268 
of notice. The Koala, like the P and 
Kangaroos, has 13 pairs of ribs ; but this class 
of characters will form the subject of the fol- 
lowing section. 
OsreoLocy or tae Marsupratta. 
Of the Skull—The form of the skull 
varies much in different Marsupial animals, 
but it may be said, in general terms, to re- 
semble an elongated cone, being terminated by 
a vertical plane surface behind, and in most 
of the species converging towards a point ante- 
riorly: it is also generally more depressed or 
flattened than in the placental Mammalia. The 
skull is also remarkable in all the Marsupial 
genera for the small proportion which is de- 
voted to the protection of the brain, and for the 
great expansion of the nasal cavity immediately 
anterior to the cranial cavity. 
In the stronger carnivorous Marsupials the 
exterior of the cranium is characterized by bony 
ridges and muscular impressions, but in the 
smaller herbivorous and insectivorous species, 
as the Petaurists, Potoroos, and Myrmecobius, 
the cranium presents a smooth convex surface 
as in Birds, corresponding with the smooth un- 
convoluted surface of the simple brain con- 
tained within. 
The breadth of the skull in relation to its 
length is greatest in the Wombat,* Ursine Da- 
syuret and Petaurists, in which it equals three- 
fourths of the length, and is least in the Pera- 
meles lagotis, in which it is less than one-half. 
The occipital region, which is generally plane, 
and vertical in position, forms a right angle 
with the upper surface of the skull, from which 
it is separated by an occipital or lambdoidal 
-crista. is crista is least developed in the 
Myrmecobius, Petaurists, and Kangaroos, and 
most so in the Thylacine and larger Opossums, 
in which, as also in the Koala, the crest curves 
slightly backwards, and thus changes the occipi- 
tal plane into a concavity for the firm implanta- 
tion of the strong muscles from theneck and back. 
The upper surface of the skull presents great 
diversity of character, which relates to the dif- 
ferent development of the temporal muscles, and 
the varieties of dentition in the different genera. 
In the Wombat the coronal surface offers an 
almost flattened tract bounded by two slightly 
elevated temporal ridges, which are upwards of 
an inch apart posteriorly, and slightly diverge, 
as they extend forwards to the anterior part of 
the orbit. 
The skull of the Virginian Opossum pre- 
sents the greatest contrast to that condition, for 
the sides of the cranium meet above at an acute 
angle, and send upwards from the line of their 
union a remarkably elevated sagittal crest, which, 
in mature skulls, is 6 gag a at more deve- 
loped& than in any of the placental Carnivora, 
not even excepting the strong-jawed Hyena. 
The Thylacine and Dasyures, especially the 
Ursine Dasyure, exhibit the sagittal crest in a 
somewhat less degree of development. It is 
again smaller, but yet well marked in the Koala 
and Perameles. e temporal ridges meet at 
* As 15 to 20. +t As 10 to 14. 
MARSUPIALIA. 
the lambdoidal suture in the larger Ph 
and in the Hypsiprymni, but the size 
muscles in these does not require the de 
lopment of a bony crest. we 
In the Kangaroo, the temporal ri wh 
are very slightly raised, are y 
interspace of the third of an inch. al 
They are separated for a proportion: 
greater extent in the Petaurists, est 
Petaurus flaviventer ; and in the smoot 
convex upper surface of the skull of Peta 
sciureus, Pet. pigmeus, Myrmecobius, thi 
pressions of the feeble temporal muscles 
cease to be discernible. 2 
The zygomatic arches are, however, com 
in these as in all the other genera: the 
usually, indeed, wnat pr ; but 
variations do not indicate the nature o 
food so clearly, or correspond with the. 
rences of animal and vegetable diet in the 
degree as in the placental Mammalia. 
this is not surprising when we recollect thi 
Marsupial animal is devoid of incisors it 
upper jaw, like the ordinary Ruminants o 
placental series : accordingly the more — 
pete dental system with which the herbiyo 
angaroos, Potoroos, Phal &c. are 
vided, and which appears to be in relatic 
the scantier pasturage and the dry and 
character of the herbage or foliage on 
they browse, requires a stronger apparatt 
bone and muscle for the action of the jaws 
especially for the working of the tert 
teeth. There are, however, well marked ¢ 
rences in this part of the Marsupial skull. 
the weakest zygomatic arches are those 
Insectivorous Perameles and é 
which structure we may discern a corres 
dence with the Edentate Anteaters of the 
cental series. Still the difference in the ¢ 
lopment of the zygomata is greatly in favo 
the Marsupial Insectivora. q 
The Hypsiprymni come next in the ore 
development of the zygomatic arches; wi 
again are proportionally much stronger 
true Senescona The vength of the zygo 
in relation to the entire skull is greatest in 
Koala and Wombat. In the former 
they are remarkable for their depth and 
and parallel course, as well as for their 
tudinal extent. In the Wombat they ha 
considerable curve outwards, so as gre 
diminish the resemblance which otherwise 
ists in the form of the skull between this } 
supial and the Herbivorous Rodentia of 
placental series, as, e.g. the Viscaccia. _ 
In the carnivorous Marsupials the out 
sweep of the zygomatic arch, which is grez 
in the Thylacine und Ursine ‘a 
accompanied by a slight curve up : 
this curvature is chiefly expressed by the 
cavity of the lower margin of the zygoma 
is by no means so well marked as in 
placental Carnivora. It is remarkable that th 
upward curvature is greater in the ( 
zygomata of the Perameles than in the stror 
zygomata of the Dasyures and Opossums. | 
the Koala and Phalangers there is also a sligl 
tendency to the upward curvature; in th 
, 
