278 MARSUPIALIA. 
tebre both by anchylosis and partial ju netic 
with the ossa innominata. 
are thirteen dorsal vertebre and thirteen pairs 
of ribs.* 
In the Koala the length of the spine of the 
first dorsal hardly exceeds that of the last 
cervical, but in all other Marsupials the diffe- 
rence is considerable, the first dorsal spine 
being much longer: those of the remaining 
dorsal vertebra progressively diminish in length 
and increase in breadth and thickness. They 
slope backwards towards the centre of motion, 
which in Mauge’s Dasyure is shown to be at 
the ninth dorsal vertebra, by the verticality of 
its spine, towards which both the preceding 
and succeeding spines incline. In the Pera- 
meles the centre of motion is at the eleventh 
dorsal vertebra, in the Potoroo and Kangaroo 
at the twelfth, in the Petaurists at the thir- 
teenth vertebra. In the Phalangers, Opossum, 
Koala, and Wombat the flexibility of the spine 
is much diminished, and the centre of motion 
is not defined by the convergence of the spinous 
rocess towards a single vertebra, but they all 
incline slightly backwards. 
The lumbar vertebre are four in number in 
the Wombat, seven in the Petaurists, and six 
im other Marsupialia; the total number of true 
vertebre being thus the same in all the genera. 
The pressure which the trunk of the Wombat 
must occasionally have to resist in its extensive 
subterranean burrows, is probably the condition 
of the development of the additional pairs of 
ribs in that species. 
The anterior oblique processes, which begin 
to increase in length in the three posterior dorsal 
vertebra, attain a great size in the lumbar ver- 
tebre, and are locked into the interspace of the 
posterior oblique processes which are double on 
each side, except in the Perameles, and in the 
last lumbar vertebre of all the other genera. 
The transverse processes of the lumbar vertebrae 
oe increase in length as the verte- 
rz approach the sacrum ; they are most deve- 
loped in the Wombat, where they are directed 
obliquely forwards. In the Kangaroos, Poto- 
roos, and Perameles, they are curved forwards 
and obliquely downwards. The length of these 
and of the anterior oblique processes is rela- 
tively least in the Petaurists, Phalangers, and 
Opossums. 
Sacrum.—The numberof vertebra succeeding 
the lumbar which are anchylosed together in 
the sacral region of the spine, amounts in the 
Wombat to seven (fig. 102), but if we regard 
those vertebre only as sacral which join the ossa 
innominata, then there are but three. In the 
Phalangers there are generally two sacral ver- 
tebre, but in the Phalangista Cookii the last 
lumbar assumes the character of the sacral ver- 
* Cuvier assigns only twelve dorsal vertebre to 
the Kangaroo Rat, but in two different species of 
i in the Mus. Coll. Surgeons, there 
are thirteen dorsal and six lumbar vertebra, and 
Fo aad the same number in the skeletons of 
ypsiprymnus ursinus and dorcocephalus in the 
Leyden Museum. Pander and D’Alton figure 
thirteen dorsal vertebre in the Hypsiprymnus mu- 
remus. 
+ In Phal. Cookii the sixth lumbar vertebra is 
joined by a part of its transverse processes to the 
ossa innominata, 
of the powerful hinder extremities is trans’ 
to two anchylosed vertebra. 
there is only a single sacral vertebra, the s 
of which is shorter and thicker than those ¢ 
lumbar vertebra, and is turned in the cont 
direction, viz. backwards. 
vertebra by anchylosis, two of which join 
ilia. In Mauge’s Dasyure, two sacral ve 
tebre are anchylosed, but it is to the expand 
transverse processes of the anterior one 
that the ossa innominata are joined. The sat 
kind of union exists in the Viverrine Da 
syure, but three vertebre are anchylose 
gether in this species. 
and Petaurists there are two sacral vert 
In Petaurus macrurus three are 
together, though only two join the ilium. 
the Wombat (fig. 102) the transverse 
cesses of the numerous anchylosed vertebrae 
remarkable for their length and flatness, tht 
of the first four are directed outwards and 
confluent at their extremities; the remai 
ones are turned in a slight degree backwat 
and very nearly reach the tuberosities of ” 
ischia, behind which they Sipe ir 
in size and disappear in the three ca 
vertebra. The transition from the sacral to 
caudal vertebre is very obscure in the Wor 
If we limit the sacral to the three v 
the ilium, then there remain twelve 
for the tail. The spinal canal is com 
all but the last three, which consist only © 
body. There are no inferior spines, anc 
the six posterior vertebrae, which progre: 
diminish i 
aperture of the pelvis, the tail is scarcely vi 
in the living animal. In the Koala (fig. 1 
the tail is also very short. In the Chen 
it seems to be wanting. 
Perameles I find eighteen caudal 
~ (OL, 
Pelvis of the Wombat. 
In the Kangaroos and Potoroos the im peti 
In the Pera nel 
r 
In the Myrmecobius there are four 
In the 
a 
ae 
in length, extend beyond the poste 
In one specie 
