This order is mainly Australian at the present day, using the term of course in the "regional" sense (see p. 84); the only exception indeed to this statement is the occurrence of the genus _Caenolestes_ in South America. But it is now known that Diprotodont Marsupials formerly existed in the same part of the world. [Illustration] FIG. 64.--Bones of right foot of Kangaroo (_Macropus bennetti_). _a_, Astragalus; _c_, calcaneum; _cb_, cuboid; _e_^3, ento-cuneiform; _n_, navicular; _II-V_, second to fifth toes. (From Flower's _Osteology_.) {130} [Illustration] FIG. 65.--Skeleton of Wallaby (_Macropus ualabatus_). The scapula is raised somewhat higher than in nature. The end of the tail is omitted. The head of the femur has been separated from the acetabulum. _acet_, Acetabulum; _acr_, acromion process; _ast_, astragalus; _cal_, calcaneum; _cbd_, cuboid; _chev_, chevron-bones; _cl_, clavicle; _cun_, cuneiform of carpus; _epi_, epipubis; _fb_, fibula; _fem_, femur; _hd_, head of femur; _hu_, humerus; _il_, ilium; _isch_, ischium; _obt_, obturator-foramen; _orb_, orbit; _pis_, pisiform; _pub_, pubis; _rad_, radius; _rb_^1, first rib; _rb_^{13}, last rib; _sc_, scapula; _st_, sternum; _tb_, tibia; _troch_, great trochanter of femur; _uln_, ulna; _unc_, unciform; _IV_, fourth toe. (From Parker and Haswell's _Zoology_.) FAM. 1. MACROPODIDAE.--This family contains the Kangaroos, Wallabies, Rat-Kangaroos, and Tree-Kangaroos. With the exception of _Dendrolagus_ the family is terrestrial, and its numerous species progress by leaps effected by the long hind-limbs, which are decidedly, often greatly, longer than the fore-limbs. In the hind-limb the fourth toe is very long and strong; the fifth moderately so; the second and third are slender and united by skin. The tail is always long, but differs in its characters from {131} genus to genus. The stomach is much sacculated. The dental formula is I 3/1 C (1 or 0)/0 P 2/2 M 4/4. The atlas is often open below, forming thus an incomplete ring. Though the number of the incisor teeth in the adult Diprotodonts is never more than three on each side in each jaw, more numerous rudiments are present. Mr. M. Woodward[76] has lately investigated the subject with interesting results. He finds that many species present decided traces of two additional incisors, raising the total to that which characterises the Polyprotodontia; but in two cases, viz. _Macropus giganteus_ and _Petrogale penicillata_, a sixth is present, the total number being thus in excess of that found in any other Marsupial. This, as the author himself admits, proves too much. No mammal is known which in the adult condition has so many incisors; nor do the fossil Mammalia help us to get over the difficulty; even among reptiles it is not usual for so many teeth to occur upon the premaxillaries.