274 
ferous remains hitherto discovered in the se- 
condary formations, will justify the minuteness, 
perhaps tediousness, with which I have dwelt 
on characters that, inclusive of the teeth, serve 
to distinguish the cranium of the Marsupial 
from that of any Placental quadruped. e 
structure of the bony palate in the Marsupials 
is interesting in other respects. Since the de- 
fective condition of this part of the cranium is 
one of the characteristics of the skull of the 
Bird, it might be expected that some approx- 
imation would be made to that structure in the 
animals which form the transition between the 
Placental and Oviparous Classes. We have 
already noticed the large vacuities which occur 
in the bony palate of nearly all the Marsupials ; 
but this imperfectly ossified condition is most 
remarkable in the great Perameles lagotis and 
Acrobates. In the former (fig. 96) the bony 
Fig. 96. 
= Perameles lagotis. 
roof of the mouth is perforated by a wide 
oval space extending from the second pre- 
molars to the penultimate molars, exposing to 
view the vomer and the convolutions of the 
inferior spongy bones in the nasal cavity. Be- 
hind this space there are six small perforations, 
two in a transverse line midway batween the 
great vacancy and the posterior margin of the 
bony palate, and four in a transverse line close 
to that margin. In Acrobates a still larger pro- 
rtion of the posterior part of the palate is 
ormed by membrane. 
MARSUPIALIA. 
Cavity of the cranium.—The Ferg: 
cranial cavity are remarkable for their thickne: 
in some of the Marsupial genera. In th 
Wombat the two tables of the parietal bone: 
are separated posteriorly for the extent of mor 
than Fait an inch, the insters being lle 
with a coarse cellular diploé ; the frontal bone 
are about two and a half lines thick. In | 
Ursine Dasyure the cranial bones havea 
milar texture and relative thickness. ' 
Koala the texture of the cranial bones is der 
and their thickness varies from two lines toh 
a line. In the Kangaroo the thicknes 
considerably in different parts of the 
the parietes are generally so thin as tot 
sar which is the case with the 
arsupials, as the Potoroos and Petaw: 
The union of the body of the second : 
of the third cranial vertebra takes place in| 
marsupial as in the placental Mammalia at 
sella turcica, which is overarched by the b 
ward extension of the lesser ale of the sphen 
The optic foramina and the fissure las 
anteriores are all blended together, so thi 
wide opening leads outwards from each sid 
the sella. Immediately posterior and 
to this opening are the foramina rotunda, 1 
each of which in the Kangaroo a remar 
groove leads to the fossa Gasseriana at the e¢ 
mencement of the foramen ovale ; s 
groove is indicated in a slight degree 
Dasyures and Phalangers, but is almost 
solete in the Wombat and Koala. The c 
canals pierce the body of the sphenoid, a 
Birds, and terminate in the skull 
together behind the sella turcica, which is 
bounded bya _ posterior clinoid process. — 
sphenoidal bulla, which forms the chief pa 
the tympanic cavity in the Perameles la 
forms a large convex protuberance on each 
of the floor of the cranial cavity in that spe 
The petrous bone in the Kangaroo, Koala, 
Phalangers is impressed above the 1 
auditorius by a deep, smooth, round pit, 1 
lodges the lateral appendage of the cereb 
The corresponding pit is shallower in the 
syuri, and is almost obsolete in the Wor 
The middle and posterior fissure lacera 
the usual relative position, but the latter 
small. The condyles are each perforated 
norly by two foramina in most of 
cops, the Thylacinus forming the exeeé 
Of the composition and form of the for 
magnum we have already spoken: it 
great size in relation to the capacity © 
cranium ; the aspect of its plane is back 
and slightly downwards. " 
In the Kangaroo and Phalancer a thin 
of bone extends for the distance of one oF 
lines into the periphery of the tentorial p 
of the dura mater, and two sharp spine 
sent down into it from the upper part 0 
cranium in the Phalangista on ina. ne 
torium is supported by a thick ridge of bo 
in the Thylacine; but it is not comple 
ossified in any of the Marsupials: in 
species, indeed, as the Dasyures, the K 
and the Wombat, the bony crista above ¢ 
scribed does not exist. There is no ossif 
or 
= 
