ORDER UNGULATA. 



1359 



and Miohippus may be united. The dental formula is the typical 

 one ; the upper premolars are as complex as the true molars (fig. 

 1 231), the external surface being without a median vertical ridge; 

 the first lower premolar is comparatively small ; and the third lobe 

 of the last lower true molar is reduced to a small talon ; while the 

 incisors have no infolding of the enamel at their summits. Some 

 species show a " larmial " depression in the 

 lachrymal. The typical A. aurelianense (fig. 

 1 231), of the Middle Miocene of the Con- 

 tinent, is the largest species, and shows no 

 trace of the fifth metacarpal • while the 

 meso- and entocuneiform of the tarsus are 

 united. In the smaller A. Bairdi of the 

 Miocene of North America the lateral digits 

 are relatively larger, the fifth metacarpal is 

 represented by a splint, and the meso- and 

 entocuneiform are separate. Allied to this 

 genus are Anchippus, Parahippus, and Hyo- 

 hippus of the North American Miocene. 



Family Proterotheriim:. — In this place 

 it may be convenient to notice the genus Pro- 

 terotherium from the Tertiary of Patagonia, 

 which was at first regarded by Dr Ameghino 

 as belonging to the Artiodactyla, but was 

 subsequently made the type of a distinct 

 family of this suborder. One species was 

 referred by Bravard to Anoplotherium^ while 

 a second was subsequently described by Dr 

 Burmeister first as Anchitherium, and then 

 as A?iisolophus. The upper premolars are 

 nearly as complex as the true molars. The 

 names Thoatheriu?n, Diadophorus, and Li- 

 caphrium have been applied to allied forms 

 from the same deposits. The lower molars 

 have four distinct roots. It may be ques- 

 tioned whether these forms are really en- 

 titled to form a distinct family. 



Family Equid^e. — The division between 

 this family and the Pal&otheriidtz is a more 

 or less arbitrary one. In the present one the 

 upper premolars are as complex as the true molars, and all the 

 cheek-teeth are usually of an extremely hypsodont type, with their 

 valleys filled with cement ; the crowns of the lower molars are cres- 

 centoid, with complex folds of enamel, and there is scarcely any 

 distinct third lobe to the last lower molar. The digits may be 



Fig. 1232. — Lateral view of 

 the right manus of the Horse 

 {Equus caballus). Reduced. 

 ca, Carpus ; m, 3d Metacar- 

 pal (cannon-bone) ; s, Lateral 

 do. ; 1, 2, 3, Phalangeals of 

 third digit. 



