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, Clucropus 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 ones than in any other climbing Marsupial. But some of the Phalangers, as the Ph. Cookii and Ph. glirifornas 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 Ritremitics.—The pelvis (fig. 109) 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 marsupialla or Janitores Marsupii.
\Ve 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 the pubis to the ischium on each side of the symphysis.
In the Kangaroos, Potoroos, Phalangers, and Opossums the ilia offer an elongated pris matic form. They are straight in the Opossum, but gently curved outwards in the other Mar supial genera. In the Dasyures there is a lon gitudinal groove widening upwards in place of the angle at the middle of the exterior surface of the ilium. The ilia in the Petaurists are simply compressed, with an almost trenchant anterior margin. They are broader and flatter in the Perameles, and their plane is turned outwards. But the most remarkable form of the ilia is seen in the Wombat, in which they are considerably bent outwards at their anterior extremity. In the Kangaroos and Potoroos the eye is arrested by a strong pro cess given off from near the middle of the ileo-pubic ridge, and this process may be ob served less developed in the other Marsupialia. The tuberosity of the ischia inclines outwards in a very slight degree in the Dasyures, Opos sums, Phalangers, Petaurists, and Perameles, in a greater degree in the Kangaroos and Poto roos, and gives off a distinct and strong obtuse process in the Wombat, (fig. 108,) which not only extends outwards but is curved for wards. In the Potoroos the symphysis of the ischia, or the lower part of what is commonly called the symphysis pubis, is produced ante riorly. The length of this symphysis, and the straight line formed by the lower margin of the ischia is a characteristic structure of the pelvis in most of the Marsupials.
elongated, flattened, and more or less curved, expanded at the proximal extremity, which sometimes, as in the Wombat, is articulated to the pubis by two points ; they are relatively straightest and most slender in the Perameles; shortest in the Myrmecobius, where they do not exceed half an inch in length ; longest, flattest, broadest, and most curved in the Koala, where they nearly equal the iliac bones in size. They are always so long that the cremaster muscle winds round them in its passage to the testicle or mammary gland, and the uses of these bones will be described in treating of that muscle.