VERTEBRATA: MAMMALIA. 



693 



into the single order of the Ungulata, or Hoofed Quadrupeds, 

 and the following are the characters of the order : 



All the four limbs are present, and that portion of the toe which 

 touches the ground is always encased in a greatly-expanded nail, 

 constituting a " hoof" Only in a few extinct forms (the Cory- 

 phodontidce] are there more than four full-sized toes to each limb. 

 Owing to the encasement of the toes in hoofs, the limbs are useless 

 for prehension, and only subserve locomotion ; hence clavicles are 

 always wanting in the entire order. There are always two sets 

 of enamelled teeth, so that the animal is diphyodont. The molar 

 teeth are massive and have broad crowns, adapted for grinding 

 vegetable substances. 



In accordance with the number of the digits (fig. 388), the 



Fig. 388. Feet of Ungulata. A, Fore-foot of Tapir (Tapirus Malayanus) ; B, Perisso- 

 dactyle fore-foot of Rhinoceros Sumatrensis; C, Artipdactyle foot of Pig (Sus 

 scrofa). The figures indicate which of the normal five digits are present in each foot. 

 (After Flower.) 



order Ungulata is divided into two primary sections : The 

 Perissodactyla, in which the toes or hoofs are odd in number 

 (one or three, or, in the extinct Coryphodontida, five), and the 

 Artiodactyla, in which the toes are even in number (two or 

 four). 



PERISSODACTYLE UNGULATES. 



SECTION A. PERISSODACTYLA. The section of the Perisso- 

 dactyle Ungulates includes the Rhinoceros, the Tapirs, the 



