_Macrotherium_, like the last genus, seems to have been common to both New and Old Worlds. It is to be distinguished by a number of characters. It is supposed to have been "semi-arboreal and fossorial"; the fore-limbs are much longer than the hind, the relative proportions of the radius and tibia being 70 to 29. The ulna was distinct from the radius, whereas in _Chalicotherium_ the two are coalesced, or nearly so. Young specimens appear to possess a full set of incisors; whether this is the case or not with _Chalicotherium_ is not known.[133] _Homalodontotherium_ is sometimes placed in the group. SUB-ORDER 4. TYPOTHERIA. It is a little difficult to be confident that the Typotheria are rightly referred to the Ungulata, since they contradict two important Ungulate rules. They have clavicles, which are elsewhere missing, and the thumb looks as if it were opposable.[134] An Ungulate is essentially a running animal, and has no need of a grasping finger. Still Typotheria are placed by most within the Ungulate series, though their undoubted likenesses to other groups, especially to the Rodentia, are admitted, and indeed emphasised. Cope places them definitely with the Toxodonts. The Typotheria are an extinct group of smallish beasts, confined, like the Toxodontia, to South America, a region which during the Tertiary period, and into the Pleistocene, abounded with strange and varied types of Ungulate animals. The earlier forms of Typotheria may be exemplified by some {213} account of the genus _Protypotherium_. This animal was of about the size of a _Hyrax_, which indeed it resembles in several points of structure. The teeth have the primitive number of forty-four, and they are close set, leaving no diastema; the molars are rootless and grow persistently; they are simple and Rodent-like in surface pattern. The shape of the lower jaw is like that of _Hyrax_, being rounded in outline posteriorly; there is no projecting angle as in the Rodents, and this remark applies to the Typotheria in general. The aspect of the Rodent lower jaw is characteristically different from that of _Hyrax_ and the forms under consideration. Some other characters of these early forms of Typotheria can be gathered from an inspection of other genera. In _Icochilus_ both hand and foot were five-toed, and, as in ancient Ungulates generally, the bones of the wrist and of the ankle are serially and not alternately arranged. Moreover, an os centrale is present in the carpus. Both thumb and big toe were opposable. The skull has a remarkably Rodent-like appearance, but the palate is not so narrowed as in these animals.