When moving with great velocity, the Kangaroo depends upon the hind limbs alone, bounding along with great ease, over ten, fifteen, or more feet at a jump. Its body is then carried almost horizontally, and the tail is stuck out as if to balance it.
SKELETON OF THE GREAT KANGAROO.
If the short fore limbs are examined, they will be noticed to be able to do a great deal in the way of holding, clasping, and turning things about, and they are used in patting the little ones, and in embracing and cleaning them. The five digits, or fingers, have a very free movement, and the fore arm can twist and turn like that of the higher animals; that is to say, it is capable of pronation and supination. The first digit, or thumb, has two joints (phalanges), and the other four have three; and the five curved claws (the third and fourth being large) are useful weapons of offence. But they and the fingers are often used for very different purposes, and they have, in the female, to open the curious pouch for the young ones, and to place them there. There is an evident relation between the arrangement of the bones of the wrist and this necessary office or function. The marsupium, or pouch, is a kind of inbending of the skin of the lower part of the belly, and is moist and naked inside. In it, in the females, are the nipples of the mammary glands, and to these the very young Kangaroos[84] hang on for a long time, before they see the outer world. They are put in there by the mother, when they are just born, and when very small and not perfectly formed. They grow there, and after a while, leave the nipple when they think fit. As this pouch, with its contents, would drag upon the mother, it is kept from doing so, more or less, by two bones which are found amongst the muscles of the lower part of the body, and which are attached to the front or pubic bones of the pelvis. They are called marsupial bones. They exist also in the males, but they have no open pouch, for it is, as it were, turned outwards, and contains part of the reproductive organs.
The head is long, and is remarkable for the long nose, and large full eyes, with eyelashes, for the Kangaroo is not nocturnal in its habits, like most of the Marsupials. The upper lip is split, the end of the nose or muffle is naked or hairy according to the kind, and the brain-case is small. The nostrils are at the side of the end of the muzzle, and are slit-like and oblique, and there are bristly “smellers” to the fleshy lips and chin. A slender tongue is sometimes seen for an instant whilst the Kangaroo is feeding, and if the bones of the jaws be examined, the angle, or lower part of the back of the lower jaw, will be found to be turned inwards.
The long jaws have not very many teeth, and there are two large lower front ones, or lower incisors, which project in a line with the lower jaw; they are horizontal and more or less pointed, but have an outer and inner cutting edge. The upper incisors, six in number, or three on each side of the middle line, are placed on the pre-maxillary bone, and they work up and down. They are broad and have the cutting edge below, and the outer one, on each side, is broad, grooved, and complicated by one or two folds of its enamel, which are continued from the outer side of the tooth obliquely forward and inward. There is a space or diastema behind the incisors. There are four premolars, one on each side of both jaws, and then follow four molar teeth above and below and on both sides of the mouth. The dental formula is thus—Incisors, 3–31–1; premolars, 1–11–1; molars, 4–44–4 = 28. There are no canine teeth in the adults, but their germs may be found in the very young Kangaroos. As the Kangaroo is a vegetable feeder, and delights in grass, leaves, and herbs, its teeth are eminently of a non-carnivorous kind. It may be remarked that when the mouth is closed, the cutting edges of the upper incisors come against the outer cutting edge of the long front teeth of the lower jaw. The true molars increase in size from front backwards; and the crown of each molar is squarish, but is longer than broad, and it has two principal cross ridges, which, when not worn, are tall, and have sharp edges. Besides these, there are two other transverse ridges which are smaller and not so tall. One of these is on the front part of the tooth, and the other on the hinder (in the upper molars only). Then there is a long ridge which connects the cross ones. They are all covered with enamel. When the tooth is worn, we find it presenting, according to Mr. Waterhouse,[85] two powerful loops or folds. On comparing these teeth with those of the herbivorous mammalia already noticed, a remarkable difference will be seen.
TEETH OF THE GREAT KANGAROO.
(A) Upper and Lower Jaw; (B) Upper Molar; (C) Lower Molar.
The hinder extremities consist of a nearly straight, long, cylindrical bone, the femur, which has a hemispherical joint head, and a large trochanter, which reaches above the joint; of two leg bones—the tibia, which is prismatic above and cylindrical below, but with only a slight inner ankle projection, and the fibula, which is distinct but thinned and concave in its lower half, where it is close and attached to the other bone, and forms the outer ankle projection. To these are added the bones of the ankle-joint and the clawed toes. The Kangaroo being a great jumper, and having a great tendon, the analogue of the tendo achillis of man, has a powerful projecting process of the hinder ankle bone for its attachment. But the great length of the foot is produced by the size of the fourth and fifth or two outer toes, and especially of the fourth, which often reaches a foot in length, including the metatarsal bone behind, and the pointed claw in front. The great claw looks like a long hoof, is three-sided and sharp-pointed like a bayonet, and with it the animal stabs and rips open the body of its opponent.[86] The outer claw is very small, and there is no great toe (or first), but the second and third are long and slender, and are united in a common skin, so as to look like a single toe with a double nail, the hair coming to the roots of it. The long narrow foot is nearly as long as the leg bones, and is admirably adapted for jumping forwards, as well as sideways, and for supporting, when the legs are widely separated, the weight of the erect body. The body in that position has the leg bones straight, the thigh bones oblique, and the pelvis and spine erect, the great tail being a prop behind. Owen remarks that in man it is the massive and expanded muscles of the back of the pelvis and upper part of the thigh, or the gluteal muscles,[87] which are the chief structures in maintaining the erect posture. But in the Kangaroo, the narrow bones of the haunch could not afford attachment to great gluteal muscles; so a muscle which is but slightly formed in man, and is called the little psoas, is greatly developed in the Kangaroo, and has evidently the power of maintaining the erect posture, although it is situate within the body and in front of the spine. The great jumping power is due to the leverage of the ankle and long toes, and the muscles which supply the tendon already mentioned, and others which have the same office. These are of great strength and size, and there are some accessory muscles to the thigh and leg. The long spine of the back has powerful processes, and the jar of the great jumps is received by two vertebræ which, anchylosed or united together, form the sacrum. The tail is made up of many vertebræ, and covered with muscles. The great blood-vessels running underneath it have many chevron, or V-shaped, bones, to protect them from pressure. The marsupial bones, one on each side, are long, and broad below; they are movable on the pubis, and afford attachment to muscular fibres, act as a pulley for others, and strengthen the walls of the abdomen. Formed within muscles and tendons, they are rather bony growths than parts of the true skeleton, and hence they may be absent in some of the order, although they are always present in the Kangaroos.
Although well provided with strong limbs and muscles, and acute senses, the Kangaroos living the life of the deer and cattle of other regions than Australia, are subject to the attacks of beasts of prey and hunters. In Australia the great Carnivora do not exist, but there is a native dog, the Dingo, aborigines, and trained dogs and colonists, who enjoy a Kangaroo hunt. The native dogs stalk and run them down, the natives spear them after sometimes forming a great circle and closing in and yelling and shouting. But the rifle and trained hounds have dislodged many more than the natives, and the animals are becoming scarcer near the settlements than in former years. Dogs which run by sight afford many an exciting hunt, and the Kangaroo starts off, bounding at a great rate, and clearing all sorts of impediments with ease. It is hard riding to keep up with the chase, and especially in hot weather, when the Kangaroo often escapes, thanks to its greater powers of endurance. Sometimes the Kangaroo will stand at bay, and will rip up a solitary Dog with its claws, or will kill with a single blow of the leg and tail. Three or more Dogs are usually laid on, one more fleet than the others, to “pull” the Kangaroo, while the others rush in and kill it. Mr. Gould[88] says that it sometimes adopts a singular mode of defending itself, by clasping its short, powerful fore limbs round its antagonist, leaping away with it to the nearest water hole, and then keeping it beneath the water until drowned.