period, and for a long time after, there were no types referable to the Camelidae in the Old World. Though a Camel in many features of its organisation, Poebrotherium was "generalised" in many ways. Thus the metacarpals and metatarsals were not fused to form a cannon bone, and the two lateral digits were represented by splint rudiments of metacarpals and metatarsals. The dentition was complete. The skull though distinctly Tylopodan, also shows more generalised characters. Thus the orbit is not quite, though nearly, completed by bone. In the Camel it is quite closed. The nasal bones are much longer, reaching nearly to the end of the snout. The odontoid process of the axis vertebra is not spout-like as in existing forms, but cylindrical, though slightly flattened upon the upper surface. The scapula is described as being more like that of the Lama than of the Camel, though variations occur which approximate to the Camel. The brain, judging of course from casts, has those sulci "which are common to the whole series of Ungulates, and closely resemble those of a foetal Sheep."
Fig. 151.—Anterior surface of axis of Red Deer, × ⅔. o, Odontoid process; pz, posterior zygapophysis; sn, foramen for second spinal nerve. (From Flower's Osteology.)
Later in historical sequence than Poebrotherium, and structurally intermediate between it and Protolabis, is the Miocene genus Gomphotherium. It shows an advance in structure upon Poebrotherium, in that the orbit is completely encircled by bone, though the posterior wall is thin; the lower canines instead of being incisiform are curved back as in later Camels, and separated by a wide diastema from the preceding and the succeeding teeth.
Later in age than Poebrotherium is Protolabis, a Tylopod in which the full number of teeth is still retained; its skull presents no particular changes from the Poebrotherine type; the nasals, however, are somewhat shortened.
Later still in point of time is Procamelus. In this form we have apparently an ancestral stock, whence both Camels and Lamas were derived. The upper incisors are as in existing forms, but the first and second persist for a somewhat longer time. The skull shows two well-marked types of structure; in P. occidentalis
