118 UNGULATA order vii 



The milk dentition consists usually of incisors, canines and cheek teeth. 

 The ID and CD are unlike the / and C only in that they are weaker. The 

 PD, on the contrary, offer many characteristic and systematically important 

 differences. Their number may diminish from four to three, but may also 

 remain unchanged, even though they are followed by only three P. The 

 posterior D has always the construction of a molar. In the lower jaw of the 

 artiodactyls D^ has a third, although small, pair of cusps, and the lower D^ 

 of the perissodactyls is often more complicated than the molars. 



The skull of the ungulates exhibits considerable differentiation. The 

 cranial cavity of the most primitive ungulates is very small, the hemispheres 

 of the cerebrum are slightly furrowed and leave the cerebellum uncovered. 

 The size and complexity of the cerebrum of the higher types increase con- 

 siderably. The skull of the earliest representatives of the ungulates has no 

 particularly distinguishing features. It is low, has a flat roof and a well- 

 developed sagittal crest on the narrow cranium. Specialisation in several 

 directions takes place, however, with the gradual evolution of the group. 

 Thus the frontals may be filled with air-cavities, or may bear horns, as in 

 artiodactyls. The basifacial axis, parallel as a rule to the basicranial axis, 

 may in some cases become inclined to it. With enlargement and development 

 of the nasals and the orbits the skull assumes a very characteristic appearance, 

 which may become still more intensified by the ossification of certain pro- 

 tuberances on the snout. 



The Ungulata are now distributed in all parts of the globe with the 

 exception of Australia. In the Tertiary they were scarcely less abundant 

 than now. 



Only those forms which had bunodont ancestors, or at least whose ancestors 

 possessed a normal canine and display well-marked specialisations in the 

 extremities, can be properly included among the Ungulata. Thus they can be 

 divided into five suborders : Condylarthra, Litopterna, Perissodadyla, Artiocladyla 

 and Amhlypoda. The relationship of the last suborder to the bunodont forms 

 is, however, somewhat uncertain. 



Suborder A. CONDYLARTHRA Cope.^ 



Extinct plantigrade ungulates with pentadactyl extremities. Astragalus with 

 elongated neck, usually with foramen, and convex distal articular surface. Carpals 

 arranged in tioo rectilinear series. Dentition complete. Cheek teeth bunodont. 

 Humerus with entepicondylar foramen. Femur with third trochanter. 



The Condylarthra are, with the exception of a few scattered remains from 

 the oldest European Eocene, restricted to the oldest Tertiary of western North 

 America (Puerco, Torrejon and Wasatch beds). They are unquestionably the 

 most primitive of ungulates, from which the perissodactyls, artiodactyls, 

 and possibly the South American Litopterna originated. They display many 

 creodont features in their cranial and skeletal structure, and probably arose 

 from a common stock. 



1 Cojye, E. D., The Condylarthra. Amer. Naturalist, 1884, p. 790, 892. Trans. Amer. 

 Philos. Soc, 1888, p. 2^$,.— Matthew, W. D. Bull. Amer. Mus. Nat. Hist., New York, 1897, 

 p. 293. — Matt/tew aiKl Gra7iger. Ihid., 1915. — Oshorn, H. F., and Eaiie, C. Ibid., 1895, p. 47. 

 — Osborn, H. F. Ibid., 1898, p. 159. 



