146 



UNGULATA 



ORDER VII 



actual construction of the teeth is very close to that in EoUppiis.) In all 

 later Equidae the cheek teeth are lophodont. The premolars of the permanent 

 dentition, above and below, always replace three milk teeth ; the most anterior 



milk tooth is not generally 

 ^ ^ '^ succeeded by a premolar. 



In all Equidae the two 

 posterior milk teeth have 

 the structure of the an- 

 terior molars, and in the 

 heterodont genera are 

 always more complete than 

 their successors. 



In the oldest forms the 

 extremities are stout ; in 

 the later ones they are 

 long and slender. The 

 ossicles of the two carpal 

 series (Fig. 191) alternate 

 with each other. In later forms the magnum, which originally is small, 

 increases much in breadth, pushes the trapezoid inward, and supports the 

 lunar and scaphoid equally. In the more primitive genera four metacarpals 

 are functional. In Anchitherium, as a result of the expansion of the magnum. 



Carpus and metacarpus of Equus {A), Anchitherium (B), and Palo- 

 plotherium (C), anterior aspect, c, Cuneiform ; I, lunar ; m, magnum ; 

 s, scaphoid ; td, trapezoid ; u, unciform ; II-V, metacarpals. 



mght hind font of Equvs( A), Hipparion (B), Anchitherium {C), 

 Paloplotherium (D), and Palaeotherium (E). 



the third metacarpal gains a decided superiority over the slender lateral 

 metacarpals, the toes of which, however, still reach the ground. In Hipparion 

 and Profohippus the metacarpus increases in length, the second and fourth 

 metacarpals are slender, but still reach nearly to the lower end of the exceed- 

 ingly well-developed third metacarpal, and support short digits which no 



