182 CHAKACTEES OF EVEN-TOED BEASTS. 



videcl into two equal or subequal facets; the os mag- 

 num does not exceed, or is less than, the unciforme in 

 size, in the carpus; and the ectocuneiforme is less, or 

 not larger, than the cuboid, in the tarsus. The digit 

 answering to the third in the pentadactjle foot is un- 

 symmetrical, and forms, with that answering to the 

 fourth, a symmetrical pair. If the species be horned, 

 the horns form one pair or two pairs; they are never de- 

 veloped singly and symmetrically from the median line- 

 The post-tympanic does not project downward distinctly 

 from the mastoid, nor supersede it in any artiodactyle ; 

 and the paroccipital always exceeds both in length. The 

 bony palate extends further back than in the perissodac- 

 tyles ; the hinder aperture of the nasal passages is more 

 vertical, and commences posterior to the last m.olar tooth. 

 The base of the pterygoid process is not perforated by 

 the ectocarotid artery. The crowns of the premolars are 

 smaller and less complex than those of the true molars, 

 usually representing half of such crown. The last milk- 

 molar is trilobed. 



To these osteological and dental characters may be 

 added some important modifications of internal structure, 

 as e. g. the complex form of the stomach in the hippopo- 

 tamus, peccari, and ruminants, the comparatively small 

 and simple c^cum, and the spirally folded colon, which 

 equally indicate the mutual afl&nities of the even-toed or 

 artiodactyle hoofed quadrupeds, and their claims to be 

 regarded as a natural group of the Ungulata. Many ex- 

 tinct genera, e. g. chc^eropotamus, anthracotherium, hyopo- 

 tamus, dichodon, merycopotamus, xiphodon, dichobune, 

 anoplotherium, have been discovered, which once linked 

 together the now broken series of Artiodactyla, repre- 

 sented by the existing genera hippopotamus, sus, dico- 



