Page:Encyclopædia Britannica, Ninth Edition, v. 13.djvu/873

KANGAROO 839 and tapers forward to the muzzle. The shoulders and fore limbs are feebly developed, and the hind limbs of dispro portionate strength and magnitude, which gives them a peculiarly awkward appear ance when moving about on all fours, as they occasionally do when feeding. Rapid progression is, however, performed only by the powerful hind limbs, the ani mal covering the ground by a series of immense bounds, during which the fore part of the body is inclined forwards, and balanced by the long, strong, and tapering tail, which is carried horizontally back wards. When not moving they often assume a perfectly upright position, the tail aiding the two hind legs to form a sort of supporting tripod, and the front limbs dangling by the side of the chest. This position gives full scope for the senses of sight, hearing, and smell to warn of the approach of enemies, from which they save themselves by their bounding flight. The fore paws have five distinct digits, each armed with a strong, curved claw. The foot of the hind limb is quite different, and very peculiar in construction, being extremely long and narrow, and (with only one, lately discovered, exception) without any hallux or great toe. It consists mainly of one very large and strong toe, corresponding to the fourth of the human or other typically developed foot, ending in a strong curved and pointed claw. 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. The dental formula, when completely developed, is incisors y, canines ^-, premolars , molars on each side, giving a total of thirty-four teeth. The three incisors of the upper jaw are arranged in a continuous arched series, FIG. 2. Skeleton of hind foot of Kangaroo. Fio. 3. Skull and teeth of Bennett s Kangaroo (Macropus ben- nettii). t 1 , t 2 , i 3 , first, second, and third upper incisors ; pin, second or posterior premolar (the first having been already shed); m 1 , m 2 , m 3 , m*, the four true molars. The last, not fully developed, is nearly concealed by the ascending ramus of the jaw. and have crowns with broad cutting edges ; the first or middle incisor is often larger than the others. Corre sponding to these in the lower jaw is but one tooth on each side, but it is of great size, procumbent or directed horizontally forwards, narrow, lanceolate, pointed, and with sharp edges. Owing to the laxity of the union of the two rami of the lower jaw at the symphysis, in many species the two lower incisors can be made to work together like the blades of a pair of scissors, a very remark able arrangement not known to occur in other mammals. The canines are absent or rudimentary, always so in the lower jaw, and often deciduous at an early age in the upper jaw. The premolars are compressed, with cutting longi tudinal edges, the anterior one is always deciduous, being lost about the time the second one replaces the milk molar, so that both premolars are never found in place and use in the same individual. The true molars have quadrate crowns, provided with two strong transverse ridges, or with four obtuse cusps. In Macropus giganteus and its im mediate allies, both premolars and one or two of the anterior true molars are shed during the lifetime of the animal, 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 molar 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 fully developed near the median line of the mouth, for the pur pose of cropping the various kinds of herbage on which they feed, and ridged and tuberculated molars for crushing it, there being no tusks or canines for offensive or defensive purposes. The number of vertebras 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 hand. 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 of large size, and very complex, its walls being puckered up by longitudinal muscular bands into a great number of sacculi, like those of the human colon. The alimentary canal is long, and the caacum well developed. All the species have a marsupium or pouch formed by a fold of the skin of the abdomen, covering the mammary glands with their four nipples. In this pouch the young (which, as in other marsupials, leave the uterus in an extremely small and imperfect condition) are placed as soon as they are born ; there their growth and develop ment proceeds; and to it they resort temporarily for the purpose of shelter, concealment, or transport, for some time after they are able to run and jump about the ground and feed upon the same 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 their existence the respiratory organs are modified much as they are per manently in the Cetacea, the elongated upper part of the larynx projecting into the posterior nares, and so maintain ing a free communication between the lungs and the external surface, independently of the mouth and gullet, thus averting all danger of suffocation while the milk is passing down the latter passage. The kangaroos are all vegetable feeders, browsing on grass and various kinds of herbage, the smaller species also eating roots. They are naturally timid, inoffensive creatures, but the larger ones when hard pressed will turn