a whole series of remains of extinct, and for the most part gigantic, examples of this group of Quadrupeds.  Not to speak of Wombats and Phalangers, two forms stand out prominently as representatives of the Post-Pliocene animals of Australia.  One of these is Diprotodon (fig. 258), representing, with many differences, the well-known modern group of the Kangaroos.  In its teeth, Diprotodon shows itself to be closely allied to the living, grass-eating Kangaroos; but the hind-limbs were not so disproportionately long.  In size, also, Diprotodon must have many times exceeded the dimensions of the largest of its living successors, since the skull measures no less than three feet in length.  The other form in question is Thylacoleo (fig. 259), which is believed by Professor Owen to belong to the same group as the existing “Native Devil” (Dasyurus) of Van Diemen’s Land, and therefore to have been flesh-eating and rapacious in its habits, though this view is not accepted by others.  The principal feature in the skull of Thylacoleo is the presence, on each side of each jaw, of a single huge tooth, which is greatly compressed, and has a cutting edge.  This tooth is regarded by Owen as corresponding to the great cutting tooth of the jaw of the typical Carnivores, but Professor Flower considers that Thylacoleo is rather related to the Kangaroo-rats.  The size of the crown of the tooth in question is not less than two inches and a quarter; and whether carnivorous or not, it indicates an animal of a size exceeding that of the largest of existing Lions.

[Illustration:  Fig. 258.—­Skull of Diprotodon Australis, greatly reduced.  Post-Pliocene, Australia.]

[Illustration:  Fig. 259.—­Skull of Thylacoleo.  Post-Pliocene, Australia.  Greatly reduced. (After Flower.)]

The order of the Edentates, comprising the existing Sloths, Ant-eaters, and Armadillos, and entirely restricted at the present day to South America, Southern Asia, and Africa, is one alike singular for the limited geographical range of its members, their curious habits of life, and the well-marked peculiarities of their anatomical structure.  South America is the metropolis of the existing forms; and it is an interesting fact that there flourished within Post-Pliocene times in this continent, and to some extent in North America also, a marvellous group of extinct Edentates, representing the living Sloths and Armadillos, but of gigantic size.  The most celebrated of these is the huge Megatherium Cuvieri (fig. 260) of the South American Pampas.  The Megathere was a colossal Sloth-like animal which attained a length of from twelve to eighteen feet, with bones more massive than those of the Elephant.  Thus the thigh-bone is nearly thrice the thickness of the same bone in the largest of existing Elephants, its circumference at its narrowest point nearly equalling its total length; the massive bones of the shank (tibia and fibula)