280 
ing between the last nine vertebre of the 
tail, In the Petaurists, Phascogales, and Da- 
syures, where the tail acts as a balancing pole, 
or serves, from the long and thick hair with 
which it is clothed, as a portable blanket to keep 
the nose and extremities warm during sleep, 
the subvertebral arches are also present, but in 
less number and of smal'er relative size. They 
are here principally subservient to the attach- 
ment of muscles, their more mechanical office 
of defending the caudal vessels from pressure 
not being required. 
Thorax.—The ribs consist of thirteen pairs, 
except in the Wombat, which has fifteen, and 
Petaurists, which have twelve; the first is the 
shortest, and, except in some of the Petau- 
rists, the broadest. In the Pet. macrurus the 
fifth, sixth, or seventh are the broadest, and 
the ribs generally have, both in this species and 
The sternum consists of a succession of elon- 
gated bones, generally six in number, but in 
the Petaurus Taguanoides five, and in the 
Wombat four. 
The first bone, or manubrium sterni, is the 
largest, and presents in many species a triangu- 
lar shape from the expansion of its anterior part, 
and sometimes a rhomboidal figure. A strong 
keel or longitudinal process is given off in many 
species from the middle of its inferior or outer 
surface; the side next the cavity of the chest 
is smooth and slightly concave. In the Wom- 
bat, Phalangers, and others, the keel is pro- 
duced anteriorly into a strong process, against 
the Sides of which the clavicles abut: the first 
pair of ribs join the produced anterior angles of 
the manubrium, 
In the Dasyures, Opossums, Phalangers, 
and Petaurists, the manubrium is compressed 
and elongated, and the clavicles are joined to 
a process continued from its anterior extremity ; 
the small clavicles of the Kangaroo have a 
similar connexion. 
The cartilages of the true ribs (which fre- 
quently become ossified in old Marsupials) are 
articulated as usual to the interspaces of the 
sternal bones; the last of these supports a broad 
flat cartilage. 
MARSUPIALIA. 
Phascolomys fusca. 
in Pet. sciureus, a tore compressed form thi 
in the other Marsupials; but this ch 
does not exist in Petaurus Tuguanoides. Int 
Great Kangaroo they are very slender g 
rounded, except at the sternal extremities, wh 
are flattened for the attachment of the cartila 
In this species and the Bush Kangaroo, 
seven anterior pairs of ribs articulate dire 
with the sternum. The cartilages of the 
false pairs are long and bent towards the : 
num, but do not join it, nor are they cor 
but have a gliding motion one over the other. 
In the Myrmecobius there are eight pairs 
true ribs; the two last pairs are floating F 
In the Opossum there are seven pairs of © 
ribs, and six which may be regarded as cosi 
nothe. In the Petaurist six pairs out of f 
twelve, and in the Wombat six pairs only ¢ 
of the fifteen, reach the sternum (fig. 105). 
‘ 
Kes 
WAZ KE 
\ = 
Of the Pectoral Extremities—The seap 
varies in form in the different Marsupk 
In the Petaurists it forms a scalene trian 
with the glenoid cavity at the converger 
the two longest sides. 
In the Wombat it presents a remarkabl 
gular oblong quadrate figure, the neck be 
produced from the lower half of the an 
margin, and the outer surface being tray 
diagonally by the spine, which in this spe 
gradually rises to a full inch above the p 
the scapula, and terminates in a long nai 
compressed acromion arching over the nec 
reach the clavicle. r 
In the Koala (fig. 106), the superior 
does not run parallel with the inferior, bt 
cedes from it as it advances forwards, and 
passes down, forming an obtuse angle, and 
a gentle concave curvature to the neck ¢ 
scapula ; a small process extends fre 
middle of this curvature. In the Potor 
upper costa is at first parallel with the lower 
this parallel part is much shorter ; the remain 
describes a sigmoid flexure as it approach 
neck of the scapula. Pein 
In the Great Kangaroo, the Perameles, F 
langers, Opossums, and Dasyures, the wh 
upper costa of the scapula describes a sigmol 
i= 
ie 
