I3i 



CHAPTER LXI. 



CLASS MAMMALIA— continued. 



Order Ungulata. 



Order VI. Ungulata. — The Ungulata, or Hoofed Mammals, con- 

 stitute the largest and one of the most important orders into which 

 the class is divided ; all the included groups being so connected 

 together as to preclude their division into well-defined separate 

 orders. This order comprises at least seven suborders, of which 

 three are totally extinct, while all the others, with the exception of 

 the Hyracoidea, have lost a large number of family types at the 

 present day. The two first suborders — Artiodactyla and Perisso- 

 dactyla — present several features in common, and are accordingly 

 brigaded together by some authorities under the names of Ungulata 

 Vera, Clinodactyla, or Diplarthra ; while all the others are included 

 in a second division under the name of Subungulata. 



All the members of this order are adapted for a terrestrial life, 

 and in the main for a vegetable diet, although a few are more or 

 less omnivorous. Their dentition is heterodont and diphyodont, 

 and the milk-set is well developed, and not changed till late in 

 life ; and in the Perissodactyla alone among Mammals do we find 

 certain instances where the whole four premolars are preceded by 

 milk-teeth. The cheek-teeth of the more typical forms have broad 

 crowns, with either tuberculated or ridged surfaces ; and their crowns 

 are very frequently interpenetrated by deep folds of enamel, which 

 produce a complicated pattern on their worn surfaces. Except in 

 Typotherium, clavicles are always wanting. The toes, with the ex- 

 ception of Chalicotherium, are provided either with blunt, broad 

 nails, or with hoofs more or less completely encasing the terminal 

 phalangeals. The feet of existing types are digitigrade, and the 

 number of the toes varies from five to one. In all existing forms 

 the humerus has no entepicondylar foramen. The scaphoid and 



