MARSUPIALIA. 
curve, the convex pos- 
terior position of which 
varies as to its degree and 
extent. 
The subscapular sur- 
face is remarkable in the 
Perameles for its flatness, 
but presents a shallow 
groove near the inferior 
costa. In most other 
Marsupials it is more or 
less convex or undulat- 
ing. 
In the Great Kangaroo 
the supra-spinal fossa is of 
less extent than the space 
below the spine, and 
the spine is inclined up- 
In the Perameles and Dasyures the 
Scapula of Koala. 
wards. 
Prono of the supra and infraspinal sur- 
ces are reserved, and the whole spine is 
bent downwards over the infraspinal surface. 
In the Potoroos and Phalangers the acromion 
is, as it were, bent downwards so as to 
resent a flattened surface to the observer. 
le the Potoroos and Opossums this appear- 
ance is produced by a true expansion of the 
acromion. In the Perameles the coracoid 
process is merely represented by a slight pro- 
duction of the superior part of the glenoid ca- 
vity. In the Kangaroo and Potoroo it forms a 
protuberance on the upper part of the head of 
the scapula. In the other Marsupials it as- 
sumes the character of a distinct process from 
the same part, and attains its greatest develop- 
ment in the Wombat and Koala, in the latter 
of which it is forcibly curved downwards and 
inwards. 
The clavicles are present in all the Marsu- 
pials, with the exception of the genus Pera- 
meles, and probably also the Cheropus. In 
the claviculate Marsupials they are relatively 
strongest and longest in the burrowing Wom- 
bat, weakest and shortest in the Great Kanga- 
roo. In the latter they are simply curved with 
the convexity forwards, and measure only two 
inches in length. In the Wombat they are 
upwards of three inches in length, and have 
a double curvature; they are expanded and 
obliquely truncate at the sternal extremity, 
where the articular surface presents a remark- 
ably deep notch: they become compressed as 
they approach the acromion, to which they are 
attached by an extended narrow articular surface. 
In the Koala the clavicles are also very 
strong, but more compressed than in the Wom- 
bat, bent outwards in their whole extent, and 
the convex margin formed, not by a continuous 
curve, but by three almost straight lines, with 
intervening angles; progressively diminishing 
in extent to the outermost line which forms the 
articular surface with the acromion. In the 
Myrmecobius the clavicles are subcompressed 
and more curved at the acromial than at the 
sternal end. In most of the other Marsupials 
the clavicle is a simple compressed elongated 
boue, with one general outward curvature. 
_.. The humerus in the Dasyures and Thyla- 
_ cines resembles that of the Dog-tribe in the 
281 
imperforate condition of the inner condyle, but 
difiers in the more marked development of the 
muscular ridges, especially of that which ex- 
tends upwards from the outer condyle for the 
origin of the great supinator muscle. This ridge 
is terminated abruptly by the smooth tract for 
the passage of the musculo-spiral nerve. 
In all the other genera of Marsupials that I 
have examined the internal condyle of the hu- 
merus is perforated. But in some species of 
Petaurus, as Petaurus sciureus, the foramen is 
represented by a deep notch; and in the Pha- 
langista Cookii, both foramen and notch are 
wanting.* The ridge above the external condyle 
is much developed in the Petaurus macrurus 
and sciureus, and notched at its upper part, but 
this notch does not exist in Pet. taguanoides. I 
find similar differences in the development of 
the supinator, or outer ridge, in the genus 
Perameles ; in the Per. lagutts it is bounded 
above by a groove; in Per. Gunnii it is less 
developed and less defined. In the Kanga- 
roos, Potoroos, Wombat, and Koala (fig. 107), 
the outer condyloid ridge extends in the form 
of a hooked process above the groove of the 
radial nerve. In all these, and especially in 
the Wombat, the deltoid process of the hu- 
merus is strongly developed; it is continued 
from the external tuberosity down the upper 
half of the humerus; except in the Petaurists, 
where, from the greater relative length of the 
humerus, it is limited to the upper third. 
The interspace of the condyles is occasion- 
ally perforated, as in the Perameles lagotis and 
Wombat. The articular surfaces at both ex- 
tremities of the humerus have the usual form; 
but it may be observed in some 
Marsupials, as the Koala, that 
at the distal articulation the 
| externalconvexity forthe radius 
has a greater relative extent 
than usual, and the ulnar con- 
cavity is less deep. 
The bones of the fore-arm 
present little to detain our 
notice. They are always dis- 
tinct and well developed, and 
their adaption to pronation and 
supination is complete. The 
prehensile faculty and ungui- 
culate structure of the anterior 
extremities appear to have 
been indispensable to animals 
where various manipulations 
were required in the economy 
ofthe marsupial pouch. When, 
therefore, such an animal is 
destined like the ruminant to 
Humerus of the 
Koala. range the wilderness in quest 
of pasturage, the requisite 
powers of the anterior members are re- 
tained and secured to it, as has been already 
observed, by an enormous developement of the 
hinder extremities, to which the function of 
locomotion is restricted. 
* In the other species of Phalangista, and in the 
Petawrus taguanoides and macrurus, the internal con- 
dyle of the humerus is perforated, _ 
