B Poephaga. In this section are the Kangaroos (Macropodidae) and the Kangaroo-rats or Potoroos (Hypsiprymnus), all strictly phytophagous. The Kangaroos are distinguished by the disproportionate length of the hind-limbs, and disproportionate development of the posterior portion of the body as compared with the fore-limbs and fore-part of the body. The hind-legs are exceedingly long and strong, and the feet are much elongated - the whole sole being applied to the ground. The hind-feet (fig. 363) have four toes each, of which the central one (the 4th toe) is by far the largest, and the two inner toes (the 2d and 3d toes) are very small, and are united by a common integument. The hallux is wanting altogether. The tail is also extremely long and strong, and is of great assistance to the animal when standing upright upon the hind-limbs. From the length and strength of the hind-limbs and hind-feet, the Kangaroos are enabled to effect extraordinarily long and continuous bounds. In fact, leaping is the ordinary mode of progression in the typical Kangaroos; and when walking upon all fours their locomotion is slow and ungraceful. The anterior extremity of the body is very diminutive as compared with the posterior, and the fore-limbs are quite small, but have five well developed toes armed with strong nails. The head is small, with large ears, and the dental formula is:
3 - 3
0 - 0
1 - 1
1 - 1
0 - 0
1 - 1
There are therefore six upper incisors, two lower incisors (the latter horizontal, fig. 362), and no functional canines (though rudimentary upper canines are present in the young of some of the Kangaroos, at any rate). The stomach is complex, and sacculated. The Kangaroos are all herbivorous, and mostly live, either scattered or gregariously, on the great grassy plains of Australia. The "Tree-kangaroos," however, (constituting the genus Dendrolagns) live mostly in trees; and in adaptation to this mode of life, the fore-legs are nearly as long and strong as the hind-legs, the tail is not used as a support, and the claws are long, curved and pointed, while small upper canines are present. They are natives of New Guinea. The "Rock-kangaroos" form the genus Petrogale, and inhabit the mountainous regions of North-western Australia.
Fig. 364. - A, Dentition of a herbivorous Marsupial (Hypsiprymnus cuniculus), showing the upper canine (c) and the great grooved first praemolar (a a); B, Lower jaw of an entomophagous Marsupial (Perameles obesula); C, Lower jaw of a predatory Marsupial (Dasyurus ursinus). (After Giebel and Waterhouse.)
The Kangaroo-rats (Hypsiprymnus) differ from the true Kangaroos chiefly in their smaller size, and in the presence of well-developed upper canines (fig. 364, A), and in having scaly tails. They are diminutive nocturnal animals, and they live mostly upon roots.