254 BULLETIN NO. VII. 



CHAPTER VI. 



THE ARTIODACTYLA. 



THE HOOFED QUADRUPEDS. 



HIS large group of mammals is a part 

 of what was once termed Pachydermata^ 

 i. e. , the thick-skinned mammals. Throw- 

 ing out the elephants, which are really 

 very different from any other mammals 

 whatever, there certainly is a consider- 

 able degree of unity of structure among 

 the members of that group, horses and 

 cattle being structurally as well as casually associated. The 

 artiodactyle or even- toed mammals are of large or medium size 

 and of various form and habits. The herbivorous habit pre- 

 vails and the feet are usually much modified from the funda- 

 mental form. The structure of the feet furnishes the most 

 obvious distinction upon which the group is founded, since all 

 the Artiodactyla split the hoof. The two halves of the hoof 

 represent the third and fourth digits, while the first and fifth 

 digits in the living forms are not functional, but hang as use- 

 less pendants above the hoof as seen in domestic cattle. The 

 ancestral forms, so far as they have been discovered, had at 

 most four subequal toes, the first digit Ipeing always absent. 

 The hippopotamus may be reckoned as among the archaic 

 types of the group and differs from all other recent forms in 

 still retaining the four toes. In this case, as in ancestral forms, 

 the bones of the forearm and lower leg and the metacarpals and 

 metatarsals are distinct and the paired bones are nearly equally 

 developed. 



In the swine a remarkable reduction is encountered, for the 

 fifth and second digits are shortened and the bones reduced. 

 The bones are, however, still distinct and the hoofs are still 

 carried as reminders of the earlier conditions. 



