(fig. 2). Close to the outer side of this lies a smaller fifth digit,
and to the inner side two excessively slender toes (the second and
third), bound together almost to the extremity in a common
integument. The two little claws of these toes, projecting together
from the skin, may be of use in scratching and cleaning
the fur of the animal, but the toes must have quite lost all connexion
with the functions of support or progression. This type
of foot-structure is termed syndactylous.
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| Fig. 1.—The Great Grey Kangaroo (Macropus giganteus). |
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| Fig. 2.—Skeleton of right hind-foot of Kangaroo. |
The dental formula, when completely developed, is incisors 31, canines 10, premolars 33, molars 33 on each side, giving a total of 34 teeth. The three incisors of the upper jaw are arranged in a continuous arched series, and have crowns with broad cutting edges; the first or middle incisor is often larger than the others. Corresponding to these in the lower jaw is but one tooth on each side, which is of great size, directed horizontally forwards, narrow, lanceolate and pointed with sharp edges. Owing to the slight union of the two halves of the lower jaw in front in many species the two lower incisors work together like the blades of a pair of scissors. The canines are absent or rudimentary in the lower, and often deciduous at an early age in the upper jaw. The first two premolars are compressed, with cutting longitudinal edges, the anterior one is deciduous, being lost about the time the second one replaces the milk-molar, so that three premolars are never found in place and use in the same individual. The last premolar and the molars have quadrate crowns, provided with two strong transverse ridges, or with four obtuse cusps. In Macropus giganteus and its immediate allies, the premolars and sometimes the first molar are shed, so that in old examples only the two posterior molars and the incisors are found in place. The milk-dentition, as in other marsupials, is confined to a single tooth on each side of each jaw, the other molars and incisors being never changed. The dentition of the kangaroos, functionally considered, thus consists of sharp-edged incisors, most developed near the median line of the mouth, for the purpose of cropping herbage, and ridged or tuberculated molars for crushing.
The number of vertebrae is—in the cervical region 7, dorsal 13, lumbar 6, sacral 2, caudal varying according to the length of the tail, but generally from 21 to 25. In the fore-limb the clavicle and the radius and ulna are well developed, allowing of considerable freedom of motion of the fore-paw. The pelvis has large epipubic or “marsupial” bones. The femur is short, and the tibia and fibula of great length, as is the foot, the whole of which is applied to the ground when the animal is at rest in the upright position.
The stomach is large and very complex, its walls being puckered by longitudinal muscular bands into a number of folds. The alimentary canal is long, and the caecum well developed. The young (which, as in other marsupials, leave the uterus in an extremely small and imperfect condition) are placed in the pouch as soon as they are born; and to this they resort temporarily for shelter for some time after they are able to run, jump and feed upon the herbage which forms the nourishment of the parent. During the early period of their sojourn in the pouch, the blind, naked, helpless young creatures (which in the great kangaroo scarcely exceed an inch in length) are attached by their mouths to the nipple of the mother, and are fed by milk injected into their stomach by the contraction of the muscle covering the mammary gland. In this stage of existence the elongated upper part of the larynx projects into the posterior nares, and so maintains a free communication between the lungs and the external surface, independently of the mouth and gullet, thus averting danger of suffocation while the milk is passing down the gullet.
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| Fig. 3.—Skull and teeth of Bennett’s Wallaby (Macropus ruficollis bennettii): i 1, i 2, i 3, first, second and third upper incisors; pm, second premolar (the first having been already shed); m1, m2, m3, m4, last premolar and three molars. The last, not fully developed, is nearly concealed by the ascending part of the lower jaw. |
Kangaroos are vegetable-feeders, browsing on grass and various kinds of herbage, but the smaller species also eat roots. They are naturally timid and inoffensive, but the larger kinds when hard pressed will turn and defend themselves, sometimes killing a dog by grasping it in their fore-paws, and inflicting terrible wounds with the sharp claws of their powerful hind-legs, supporting themselves meanwhile upon the tail. The majority are inhabitants of Australia and Tasmania, forming one of the most prominent and characteristic features of the fauna of these lands, and performing the part of the deer and antelopes of other parts of the world. They were important sources of food-supply to the natives, and are hunted by the colonists, both for sport and on account of the damage they do in consuming grass required for cattle and sheep. A few species are found in New Guinea, and the adjacent islands, which belong, in the zoological sense, to the Australian province, beyond the bounds of which none occurs.
The more typical representatives of the group constitute the sub-family Macropodinae, in which the cutting-edges of the upper incisors are nearly level, or the first pair but slightly longer than the others (fig. 3). The canines are rudimentary and often wanting. The molars are usually not longer (from before backwards) than the anterior premolars, and less compressed than in the next section. The crowns of the molars have two prominent transverse ridges. The fore-limbs are small with subequal toes, armed with strong, moderately long, curved claws. Hind-limbs very long and strongly made. Head small, with more or less elongated muzzle. Ears generally rather long and ovate.
