402 PROF. OWEN ON THE OSTEOLOGY 
the articular surface of the fifth and the outer half of that of the fourth digit, the re- 
mainder of which abuts against the oblique proximal extremity of the middle metatarsal 
bone. 
The five metatarsal bones are all thick and short, but chiefly so the outermost. 
The innermost digit has two phalanges, the remainder three. The unguial phalanx 
of all the digits is conical, curved, convex above, expanded at the base, and simple at 
the opposite extremity. In the Perameles the unguial phalanx of the three middle digits 
of the hand, and of the two outer digits of the foot, are split at the extremity by a longi- 
tudinal fissure commencing at the upper part of the base. This structure, which cha- 
racterizes the unguial phalanges in the placental Anteaters, has not been hitherto met 
with in other marsupial genera’. 
The terminal phalanges of the Koala are large, much compressed, and curved. The 
concave articular surface is not situated, as in the Cats, on the lower part of the prox- 
imal end, but, as in the Sloth, at the upper. The claws which they support are long. 
In the Great Kangaroo the first row of the carpus is composed, as in the Wombat, 
of three bones, but the apex of the ulna rotates in a cavity formed exclusively by the 
cuneiform. There are four bones in the second row, of which the unciform is by far 
the largest, and supports a part of the middle, as well as the two outer digits. In the 
Potoroos I find but three bones in the distal series of the carpus, the trapezoides being 
wanting, and its place in one species being occupied by the proximal end of the second 
metacarpal bone, which articulates with the os magnum. In the Perameles there are 
four bones in the second carpal row, although the hand is less perfect in this than in 
any other marsupial genus, Cheropus excepted, the three middle toes only being fully 
developed. In the Petaurists the carpus is chietly remarkable for the length of the os 
pisiforme. It would be tedious to dwell on the minor differences observable in the bony 
structure of the hand in other Marsupials ; I shall therefore only observe, that though 
the inner digit is not situated like a thumb, yet that the fingers enjoy much lateral 
motion, and that those at the outer can be opposed to those at the inner side, so as to 
grasp an object and perform in a secondary degree the function of a hand. In the 
Koala the two inner digits are more decidedly opposed to the three outer ones than in 
any other climbing Marsupial. But some of the Phalangers, as the Ph. Cookii and Ph. 
gliriformis of Bell, present in a slighter degree the same disposition of the fingers, by 
which two out of the five have the opposable properties of a thumb. A similar dispo- 
sition of the fingers may be observed in the Dormouse when it climbs, and it probably 
may not be uncommon in other placental Mammals of similar habits, and which have 
long, slender, and freely moveable fingers. As a permanent disposition of the digits, 
the opposition of three to two is most conspicuous in the prehensile extremities of the 
Chameleon. ‘ 
! It would be interesting to examine the skeleton of the Cheropus with reference to this structure. 
