602 UNGULATA. 



some important respects from the perissodactyl type, e.g. the fore-foot is 

 artiodactyl-like, and the number of dorso -lumbar vertebrae is less than 22. 

 They are huge extinct beasts from the Eocene and Miocene of N. America 

 and probably of Europe. They possessed two bony horn-like prominences 

 on the nasal bones. c j^|* T P ^Tv m f grinding teeth brachyodont 

 with a W-shaped outer wall and two inner tubercles with low connecting 

 ridges. Manus with 4 digits, artiodactyl-like, axis passing between digits 

 3 and 4, pes perissodactyl with 3 digits. The bones of the two 

 carpal rows alternate. Premolars like the molars in the later forms, 

 simpler in the older ; femur with a small third trochanter, and the fibula 

 articulates with the calcaneum. The orbits were open behind. The 

 brain cavity was small and there was a small, much convoluted cerebrum. 

 There appear to have been only 19 or 20 dorso-lumbar vertebrae, a 

 character which also recalls the artiodactyls ; probably omnivorous. 

 Lambdotherium Cope, Palaeosyops Leidy, Titanotherium Leidy, Bronto- 

 therium and Brontops Marsh. 



Sub-order 3. LIPOTERNA.* 



They are remarkable extinct American digitigrade ungulates, f which 

 in the structure and reduction of their digits (the axis of the limb passing 

 through the third digit) and in the structure of their lophodont grinding 

 teeth resemble the Perissodactyla ; but they differ from them in the 

 carpal and tarsal bones not alternating, and in the fact that the fibula 

 articulates with the calcaneum as in Artiodactyls. The humerus is without 

 an entepicondylar foramen. The digits vary in number from five to one. The 

 astragalus is flattened below, the carpus has no centrale, the orbit is usually 

 closed, there is a third trochanter on the femur, and there is no clavicle. 

 The brain case is small and the dentition complete or slightly reduced. 

 The group is not well known, but the digits and the teeth show variations 

 not unlike those presented by the same organs in the Perissodactyls. For 

 instance the digits vary from five to one, the teeth show a tendency to 

 reduction in some genera, but these variations do not form a continuous 

 series as in the Perissodactyls. The oldest forms, e.g. Thoatherium f rom 

 the Eocene of Patagonia show a reduction in the teeth and of the digits 

 to the equine condition, and a diastema between the incisors and grinders, 

 whereas in the comparatively recent form Macrauchenia from the Pliocene, 

 the dentition is complete, the feet have three digits, and there is no gap 

 in the tooth series. A remarkable feature of the Macrauchenidae is the 

 presence of a mark in the incisors as in the Equidae, and in the same 

 family the vertebrarterial canal pierces the neural arches of the cervical 

 vertebrae as in the camels and My.mecophaga. It can hardly be sup- 

 posed that the sub-order is related to the Perissodactyls, but the resem- 

 blances are certainly remarkable. 



Fam. 1. Maerauchenidae. Dentition i f c p \m f in a closed row ; 

 incisors with a "mark," anterior premolars simpler than the molars, grinders 

 rhinocerotine ; nasal openings far back, nasal bones reduced or aborted ; 



* Ameghino. Contrib. al conocim de los Mammiferos foss. d. 1. Bepubl. 

 Argent., Actas Ac. nac. Cordoba, 1889, 6, p. 523, and Revista Argentina, 

 1, '1891. Cope, The Lipoterna, Amer. Sat., 25, 1881. Gervais, Mem. 

 JSoc. Geol. France, (2), 9, 1873. 



j- The reasons for placing this sub-order among the ungulates are stated 

 on p. 574. 



