In the Peophagous Marsupials no rudiment of the innermost toe exists. The power of the foot is concentrated in all these genera on the fourth and fifth or two outer toes, but especially the fourth, which, in the Great Kangaroo, is upwards of a foot in length, including the metatarsal bone and the claw. This formidable weapon resembles an elongated hoof, but is three-sided and sharp-pointed like a bayonet, and with it the Kangaroo stabs and rips open the abdomen of its assailant : with the ante rior extremities it will hold a powerful dog firmly during the attack, and firmly supporting itself behind upon its powerful tail, deliver its thrusts with the whole force of the hinder extremities.
The cuboid bone which supports the two outer metatarsals is proportionally developed. The internal cuneiform bone is present, though the toe which is usually articulated to it is wanting. It is also the largest of the three, and assists in supporting the second metatarsal; posteriorly it is joined with the navicular and external cuneiform bones, the small middle cuneiform occupying the space between the external and internal wedge-bones and the proximal extremities of the two abortive meta tarsals. The great or fourth metatarsal is straight and somewhat flattened ; the external one is compressed and slightly bent outwards; the toe which this supports is armed with a claw simi lar to the large one, but the ungueal phalanx does not reach to the end of the second pha lanx of the fourth toe, and the whole digit is proportionally weaker.
In the climbing Potoroos, ( Bypsiprymnus ursinus and Hypsipryntnus dorcocephalus), the two outer toes are proportionally shorter than in the leaping species, and are terminated by curved claws by which they gain a better hold on the branches and inequalities of trees.
Mvotoo v.— To give a description of the muscular system with the same detail as of the osteology of the Marsupials would not be at tended with the same advantages. Modified as this system necessarily is in conformity with the various modes of locomotion in the different Marsupial genera, as running, leaping, burrow ing, swimming, even flying, we should here fail to detect in these modifications so many marks illustrative of the aberrant and inferior type of structure of our present group as we have witnessed in those of the skeleton. In addition, moreover, to their physiological rela tions, the importance of the passive and endur ing parts of the locomotive system to the zoology both of recent and extinct species, con fers upon them a claim to our attention which the more perishable though more highly organ ised and active parts of the same system do not possess, even if a detailed tnyology comported with the scope and extent of the present work. The present notice, therefore, of this depart ment of the anatomy of the Marsupialia will be limited to a brief description of a few of the most striking peculiarities.
• Every one knows that the erect position is the most usual one in the Kangaroos ; yet the conditions of this posture are very different from those in the human subject. The trunk, in stead of resting on two nearly vertical pillars so placed with reference to the superincumbent weight that it rather inclines to topple forwards, is here swung upon the femora as upon two springs, which descend from the knee-joints ob liquely backwards to their points of attachment at the pelvis ; and the trunk is propped up be hind by the long and powerful tail (fig. 103). In Man the massive and expanded muscles which find their attachment in the broad bones of the pelvis, especially at the posterior part, are the chief powers in maintaining the erect posture. But in the Kangaroo the glutai offer no corresponding predominance of size; the narrow prismatic ilia could not, in fact, afford them the requisite extent of fixed attachment. The chief modifications of the muscular sys tem in relation to the erect position of the trunk in the Kangaroo are met with on the anterior part of the base of the spina] column. The psore parve, for example, present proportions the very reverse of those which suggested their name in human anatomy. They form two thick, long, rounded masses, which take their origin, fleshy, from the sides of the bodies and base of the transverse processes of the lower dorsal and all the six lumbar vertebra, and from the extre mities of the three last ribs; the fibres converge penuiformwise to a strong, round, middle tendon, inserted in the well-marked tubercle or spine of the pubis, already noticed.
The disposition of the abdominal muscles, especially at the pubic and hypochondriac re gions, has been described and figured by Mr. Morgan* and Professor Vrolikt in the female Kangaroo. The principal modifications are seen first in the presence of a large muscle called the triangularis by Tyson, the anterior rectus abdominis by Mr. Morgan,t and con sidered as the analogue of the pyramidalis muscle by Meckel ; secondly, in the equal de velopment of the cremaster in both sexes ; and thirdly, in the formation of a moveable bone in the situation and, as it were, in the substance of the mesial or internal pillar of the abdominal ring, which bone serves as a trochlea or pulley for the cremaster, and affords an extensive attachment to the abnormally developed pyra midalis. This part of the muscular system is here described as it exists in a male Phalanger (fig. 112), that sex being chosen, because most of the peculiarities, as the extensive pyramidalis,§ the cremaster, and the ossified tendons of the external oblique abdominal muscle have been regarded as being essentially connected with the physiology of the marsupial pouch, whereas they are equally developed in both sexes.