254 BULLETIN NO. VII. 
CHAPTER VI. 
Aad owedan MIG Ryo. igh dibs. 
THE HOOFED QUADRUPEDS. 
HIS large group of mammals is a part 
of what was once termed Pachydermata, 
_ Le., 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 being 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. 

