594 UNGULATA. 



Europe, premolars simpler than molars, last lower molar with talon ; 

 Heptodon Cope and Helatetes Marse, Eocene of N. Amer. ; Colodon Marsh, 

 Eocene of N. Amer., Miocene of Europe. Protapirus Filhol, Oligocene of 

 Europe ; Systemodon Cope, Eocene of Amer. ; Palaeotapirus Filhol, Eocene, 

 Eur ; Insectolophus Sc. and Os., Eocene of Eur. and Amer., etc. 



Fam. 2. Equidae.* Horses, asses, and zebras. Orbit closed. Grind- 

 ing teeth hypsodont, with much elongated tubercles or cusps and the 

 valleys filled in with cement ; i$c\p$m%, the first premolar being 

 small, without successor and early falling out. Upper molars with two 

 crescentic intermediate tubercles (six cusps in all) ; lower with a large 

 grooved pillar (anterior inner tubercle) at the junction of the two crescents 

 (see p. 595). Incisors chisel-shaped, the enamel being invaginated into 

 the crown to form the lining of a pit (the mark). Radius and ulna fused, 

 the latter being very slender distally. Manus and pes three- or one-toed, 

 the lateral digits being either complete but functionless, or reduced to 

 their metapodia (splint bones). 



Fossil remains are found in the U. Miocene, Pliocene and Pleistocene 



FIG. 310. Skull of Equus cabaUus. 



of Europe, Asia, N. Africa and America ; at the present day represented 

 solely by the genus Equus which is indigenous in Europe, Asia and Africa. 

 Equus L., the only living genus. In the upper molars both inner tubercles 

 (pillars) are connected with their respective intermediate crescentic 

 tubercles (Fig. 312, A). Manus and pes with a single complete digit, and 

 the proximal portions of metapodia 2 and 4 (splint bones). A callosity on 

 the inner side of the fore-limb above the carpus. The genus first appears in 

 theU. Miocene (? Pliocene) of India (Siwalik Hills) ; it is also found in the 

 Pliocene and Pleistocene of Europe, N. Asia, N. Africa and America. 

 Digit No. 3 alone is functional, digits 1 and 5 are entirely absent, and 

 digits 2 and 4 represented only by the proximal ends of their metapodia 

 (splint bones). The milk dentition is i f c \ m |, the permanent 



* Marsh, Amer. Journ. Sci. (3), 43, 1892. Huxley, Annual Address, 

 Ceol. Soc., Quart. J. Geol. Soc., 1870, 26. W. Kowalevsky, op. cit. For- 

 syth Major, Beitrage zur Geschichte der foss. Pferde, Abh. Schweiz. pal. 

 Ges., 4 and 7, 1877-86. Scott, Osteology of Mesohippus, etc., Journ. 

 Morph., 3, 1891. A. Ecker, Das europaische Wildenpferd, etc., Globus, 

 34, Brunswick, 1878. J. M. M'Fadyean, Anatomy cf the Horse, 1884. 

 F. H. Huth, Bibliographical Record of Hippology, 1887. 



