28 



GUIDE TO THE FOSSIL MAMMALS AND BIRDS. 



Sub-order 



-Artiodactyla. 



Pier-cases In another group of hoofed maish-dwellers of the 



T bi^^^ Eocene period the weight of the body soon became sup- 

 6-10. ported mainly by two of the middle toes (nos. in, iv), 

 which grew to be of equal size. Hence the Artiodactyla or 

 even-toed hoofed animals. In some cases, even before tlie 

 close of the Eocene period, the side-toes had dwindled and 

 practically disappeared, while the basal pieces (or meta- 



FiG. 17. — Skeleton of Fore foot of three existing Artiodactyl or Even-toed 

 Ungulata — namely, Pig (A), Deer (B). and Camel (C), much reduced 

 in size. R, radius ; U, ulna ; c, cuneiform ; I, lunar ; s, scaphoid ; 

 11, unciform ; w, naagnum ; td, trapezoid ; ii, iii, iv, v, the several 

 digits. (From Flower's " Osteolog}' of the Mammalia.") 



podium) of the pair of supporting toes became fused 

 together, thus producing the appearance of a " cloven hoof." 

 As the successive Tertiary periods followed, the >Suixa (pigs, 

 peccaries, and liippopotamus) alone retained their four 

 separate toes ; the Tylopoda (camels and llamas) gradually 

 lost their side-toes, while the bases of their middle toes still 

 remained imperfectly fused at their lower end ; the Tragu- 

 LiXA (che\Totains) and Pecora (giraffes, deer, sheep, and 

 cattle) also lost their side-toes more or less completely, and 



