The existing forms are all animals eminently adapted for a terrestrial life, and in the main for a vegetable diet. Though a few are more or less omnivorous, and may under some circumstances kill living creatures smaller and weaker than themselves for food, none are distinctly and habitually predaceous. Their teeth are markedly heterodont and diphyodont,—the milk set being well developed and not completely changed until the animal attains its full stature. The molars have broad crowns with tuberculated or ridged surfaces. There are no clavicles.[173] Their toes are provided with blunt, broad nails, or in the majority of cases with hoofs, more or less enclosing the ungual phalanges. The scaphoid and lunar bones of the carpus are always distinct. The humerus has no entepicondylar foramen. The number of digits varies from five to one; and the radius and ulna may be united together. The more generalised of the fossil forms do not conform in all respects to the above-mentioned characters; clavicles being present in _Typotherium_, and perhaps in some of the Condylarthra, while in the latter group the humerus may have an entepicondylar foramen, and thus approximate to the corresponding bone of the Carnivora. Wide as is the gap between existing Carnivores and Ungulates, there are indeed more or less strongly marked evidences of affinity between the earlier members of the two orders, as will be again noticed under the head of the suborder Condylarthra. A departure from the normal type of foot-structure is exhibited by the extinct _Macrotherium_, provisionally included in the Perissodactyla, where the digits terminated in long and curved claws. As a general rule, the cheek-teeth have distinct roots, and in those of the existing suborders a gradual increase in the height of the crowns of these teeth may be noticed in passing from the more generalised to the more specialised types. Those teeth in which the crowns are low, and their whole structure visible from the grinding surface, are termed _brachydont_ (Fig. 122); while those with higher crowns, in which the bases of the infoldings of enamel are invisible from the grinding surface, are known as _hypsodont_ (Fig. 123). Again, when the tubercles on the crowns of the molars are more or less cone-like in form the tooth is said to be _bunodont_; but when they are expanded in an antero-posterior direction and curved into a crescent shape the tooth is described as _selenodont_. [Illustration: FIG. 98.—Right fore foot of Indian Elephant. × ⅛. U, ulna; R, radius; _c_, cuneiform; _l_, lunar; _sc_, scaphoid; _u_, unciform; _m_, magnum; _td_, trapezoid; _tm_, trapezium; I to V, first to fifth digit.]