188 UNGULATA order vii 



teeth selenodont, longer than broad, usually separated from canine and frequently 

 from first premolar, by a diastema. Premolars greatly reduced, the first caniniform 

 when present. Cervicals without vertebrarterial canal. Carpals distinct; in the 

 tarsus only second and third cuneiforms coalesced. Feet four- to two-toed, in later 

 forms lateral digit? completely atrophied. Principal metapodials with distal 

 median ridges sharply limited to palmar face, as a rule co-ossified, distinct only 

 in the oldest forms. Stomach with three compartments. 



Of the two existing genera, Camelus and Auchenia, the former at present 

 inhabits Asia and northern Africa, and Auchenia is limited to South America. 

 The family originated in North America, and in the Eocene, Oligocene and 

 Miocene was wholly confined to this region. In the Pliocene it extended as 

 far as Asia, and thence into northern Africa. The extinct North American 

 types form a continuous evolutionaiy series, and are traceable back to the 

 primitive unspecialised tetradactyl Eocene forms with separate metapodials 

 and complete dentition. 



The skull bears neither horns nor antlers. Its low elongated form, 

 obliquely sloping muzzle, short premaxillary with high ascending branch, 

 the prominent orbits completely surrounded by bone, and the slight inclina- 

 tion of the facial axis toward the cranial axis, lend to it a certain physiognomic 

 similarity to that of the horse. The dentition recalls that of the ruminants, 

 although the molars are narrower, and in the upper jaw there is at least one 

 incisor and a canine, and sometimes all three incisors are present. The 

 premolars are much reduced. 



It is noteworthy that notwithstanding the early appearance of coalescence 

 of the metapodials, the carpals and tarsals always remain distinct. In the 

 carpus the trapezoid has been removed to one side and backward by the 

 remarkable broadening of the magnum, yet is still supported by the third 

 metacarpal. In later forms the trapezium is suppressed. Median keels are 

 absent on the dorsal side of the distal articular surfaces of the metapodials. 

 As regards their dental and skeletal development, fossil camels form a con- 

 spicuous and peculiar series, the older members of which may be compared 

 in certain particulars with the embryos of the existing genera Camelus and 

 Auchenia. 



Subfamily 1. Leptotragulinae Cope. 



Dentition complete, witlwut diastema, hrachyodont. Canine larger than third 

 incisor. JVith the exception of the last, premolars trenchant. Superior molars all 

 with cusps selenoid. Pioof of skull flat. Muzzle short. Metapodials not fused 

 together. Manns tetradactyl. Pes with two digits and with ptroximal splint bones. 

 Radius and ulna anchylosed in adults only. Upper Eocene (Uinta beds) and 

 Oligocene ; North America. 



Bunomery.c Wortman. Superior molars quinquetubercular : ^. P. M. similar 

 to those of Homacodon, but selenodont. Uinta beds. B. elegans Wortman. 



Proc. U.S. Nat. Mus., Washington, vol. 46, 191Z.^ Matthew, IV. D., Memoirs Amer. Mus. Nat. 

 Hist., New York, vol. i., 1901, pp. 420-439. — Peterson, 0. A., Oxydactylus. Ann. Carnegie 

 Mus., vol. ii., 1904. — Stenomylus. Ibid., vol. iv., 1908. — Miocene Camel from Nebraska. Ibid., 

 vol. vii., 1911. — Scott, ir. B., On the Phylogeny of Poebrotherium. Journ. Morphology, vol. v., 

 1891. p. 1. — The Selenodont Artiodactyla of the Uinta Eocene. Trans. Wagner Free lust. Sci., 

 Phil.id., \S99. — Wortman, J. L., The Extinct Camelidae of North America. Bull. Amer. Mus. 

 Nat. Hist.. New York, 1S9S, pp. 93-142. 



