282 



MARSUPIALIA. 



We find, therefore, that the bones of the fore- 

 arm of the Kangaroo differ little from those of 

 the burrowing Wombat, the climbing Koala, or 

 the carnivorous Dasyure, save in relative size. 

 They present the greatest proportional strength 

 in the Wombat, and the greatest proportional 

 length and slenderness in the Petaurists or Fly- 

 ing Opossums, in which the radius and ulna are 

 in close contact through a great portion of their 

 extent, and thus lend a firmer support to the out- 

 stretched dermal parachute. They are also long 

 and slender in the Koala. In general the radius 

 and ulna run nearly parallel, and the interos- 

 seous space is very trifling. It is widest in the 

 Potoroos. The olecranon is well developed in 

 all the Marsupials. In the Virginian Opossum 

 and Petaurists we find it more bent forwards 

 upon the rest of the ulna, than in the other Mar- 

 supials. In the Wombat, where the acromion is 

 the strongest, and rises an inch and a half above 

 the articular cavity of the ulna, it is extended 

 in the axis of the bone. The distal end of the 

 radius in this animal is articulated to a bone 

 representing the os scaphoides and os lunare. 



The ulna, which in the same animal con- 

 verges towards a point at its distal end, has that 

 point received in a depression formed by the 

 cuneiform and pisiform bones ; these are bound 

 together by strong ligaments, and the pisiform 

 then extends downwards and backwards for 

 two-thirds of an inch. The second row of the 

 carpus consists of five bones. The trapezium 

 supports the inner digit, and has a small sesa- 

 moid bone articulated to its radial surface. 

 The trapezoides is articulated to the index digit, 

 and is wedged between the scapho-lunar bone 

 and os magnum ; this forms an oblique articu- 

 lar surface for the middle digit; but the largest 

 of the second series of carpal bones is cuneiform, 

 which sends downwards an obtuse rounded 

 process, and receives the articular surface of 

 the fifth, and the outer half of that of the 

 fourth digit, the remainder of which abuts 

 against the oblique proximal extremity of the 

 middle metatarsal bone. 



The five metacarpal bones are all thick and 

 short, but chiefly so the outermost. The inner- 

 most digit, or pollex, has two phalanges, the 

 remainder three ; the ungueal phalanx of all the 

 digits is conical, curved, convex above, ex- 

 panded at the base, and simple at the opposite 

 extremity. 



In the Perameles the ungueal 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 longitudinal fissure commencing 

 at the upper part of the base. This structure, 

 which characterizes the ungueal 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 con- 

 cave articular surface is not situated, as in the 

 cats, on the lower part of the proximal end, 

 but, as in the sloths, at the upper. The claws 

 which they support are long. 



' It would be interesting to examine the skeleton 

 of Uie CheeropuSf with reference to this structure. 



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 ca- 

 vity formed exclusively by the cuneiforme. 

 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, Ctueropus excepted, the three 

 middle toes only being fully developed. 



In the Petaurists the carpus is chiefly re- 

 markable 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 there- 

 fore 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 deci- 

 dedly opposed to the three outer onfs than in 

 any other climbing Marsupial. But some of 

 the Phalangers, as the Ph. Cookii and Ph. 

 gliriformis of Bell, present in a slighter de- 

 gree the same disposition of the fingers, by 

 which two out of the five have the opposable 

 properties of a thumb. I have observed a 

 similar disposition of the digits in the act of 

 climbing in the Dormouse, and it probably is 

 not uncommon in other placental Mammalia 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 pre- 

 hensile extremities of the Chameleon. 



Of the Pelvic Extremities. The pelvis (fig. 

 1.09) in the mature Marsupials is composed of 

 the os sacrum, the two ossa innominata, and the 

 characteristic supplemental bones, attached to 

 the pubis, called by Tyson the ossa marsupialia 

 or Janitores Marsupii. 



We seek in vain for any relationship be- 

 tween the size of the pelvis and that of the 

 new-born young, the minuteness of which is 

 so characteristic of the present tribe of animals. 

 The diameters both of the area and apertures 

 of the pelvic canal are always considerable, 

 but more especially so in those Marsupialia 

 which have the hinder extremities dispropor- 

 tionately large ; as also in the Wombat, where 

 the pelvis is remarkable for its width. The 

 pelvis is relatively smallest in the Petaurists ; 

 but even here the diameter of the outlet is at 

 least six times that of the head of the new-born 

 young. 



The anterior bony arches formed by the ossa 

 pubis and the ischia are always complete, and 

 the interspace between these arches is divided, 

 as in other Mammalia, into the two obturator 

 foramina by an osseous bridge continued from 



