PERISSODACTTLA. 



597 



Fia. 313. — A half worn upper molar of 

 PcUaeotherium magnum (after Owen, 

 from Flower and Lydekker). //con- 

 cavities of outer wall, a postero-exter- 

 nal tubercle (metacone), 6 antero- 

 extemal tubercle (paracone), c postero- 

 internal tubercle (hypocone), forming 

 with the intermediate tubercle which 

 is not distinct the posterior transverse 

 ridge, d antero-internal tubercle 

 (protocone) forming with the not 

 distinct antero-intermediate tubercle 

 i (protoconule) the anterior transverse 

 ridge, e median valley, g posterior 

 valley. 



Pliocene of Amer. Hipparion * Christol., grinding teeth less hypsodont 



than in Equus (half the length), anterior inner tubercle of upper molar 



isolated and laminae of enamel 



more plicated than in Equus ; foot •' - 



tridactyle, outer digits not reaching 



ground, ulna rather better de- 

 veloped than in the horse, about 



the size of a donkey ; U. IVIiocene 



and PUocene of Eur., N. Amer., 



and Asia. 

 Fam. 3. Palaeotheriidae. Orbits 



not closed, grinding teeth brachy- 



odont, rooted, vaUeys not filled 



with cement ; hinder premolars 



usually like the molars, rarely 



simpler ; last lower molar with or 



without a third lobe ; u. grinders 



with W-shaped outer wall ; 1. 



grinders with two crescents which 



at their point of union form one or 



two small cusps ; radixis and ulna 



separate ; feet tridactyle, metapodia 



relatively short, the lateral digits 



reaching the ground ; U. Eocene and 



Miocene of Eur. and N. Amer. 



Palaeotherium G. Cuv., u. grinders 



with W-shaped outer wall and two 



oblique transverse ridges (Fig. 313), the intermediate and inner tvibercles 



forming the transverse ridges and not distinct from each other ; in the 



lower molars the outer tubercles are crescentic and convex outwards (Fig. 



314), but the inner tubercles (pillars of the horse) are not distinct ; the 

 three cuneiforms of the tarsus (Fig. 316, jEJ) are separate ; 

 the skull is rather tapir like, and the neck shorter than 

 in Equidae ; they attain to the size of a rhinoceros ; 

 U. Eocene of Europe. Paloplotherium Ow., the inter- 

 mediate tubercles are distinct in the u. grinders, with 

 cement ; pes (Fig. 316, D) as in the last, U. Eocene 

 of Europe. Mesohippus f Marsh, u. grinders with 

 W-shaped outer wall formed of the two V-shaped 

 outer cusps, there are four other cusps not united, 

 viz. two intermediate and two internal ; a splint like 

 metacarpal 5, in possessing which it approximates to 

 the next family ; Oligocene of N. Amer. Anchitherium X 

 H. V. Meyer (Figs. 315, C, 316, C), more horse-hke than 

 the other genera of this family, incisors slightly pitted, 

 u. grinders with W-shaped outer wall ; inner tubercles 

 connected with the outer wall by the semilunar inter- 

 mediate tubercles (the distinction between the inter- 

 mediate tubercles and the inner is not clear, as in 



* Cope, Review of N. Amer. sp. of Hippotherium, Proc. Amer. Phil. 

 Soc., 1889. 



t Osbom and Wortman, Bull. Amer. Mus. N. Hist., 7, 1895, p. 352. 

 X W. Kowaleveky, Mem. Akad. Imp. Sci., Petersbourg, (7), 20, 1873. 



Fig. 314:.— Palaeo- 

 therium crassum, 

 Cuv., anterior 

 lower molar (from 

 Zittel). p antero- 

 external tubercle. 

 a antero-internal 

 tubercle not dis- 

 tinct from (3 ; y 

 postero - external, 

 yi postero-lnter- 

 nnl tubercle, ^' 

 cusp formed 



where the cres- 

 cents meet. 



