314 MAMMALIA. 



species (placed with the sub-genus Hlppotigris Sm.) are E. quagga Gm. ; 

 E. zebra L., Zebra ; E. JBurchelli Fisch., Burchell's Zebra. 



Order 6. ARTIODACTYLA (PARIDIGITATA). 



Ungulates with paired digits, of which the two outer are usually 

 rudimentary, the two middle of equal size and rest on the ground ; 

 often without canine and incisor teeth in the upper jaw ; grinders 

 always with folds of enamel. 



Some of the Artiodactyla are unwieldly and heavily built, some are 

 slender and graceful animals, sometimes with short, sometimes with 

 long limbs ; the former with thick naked skin and a covering of stiff 

 bristles, the latter with a thick fur. They walk mainly on the 

 third and fourth digits, which are always larger than the two 

 external digits, and touch the ground with their hoofs (fig. 670 c d). 

 The second and fifth digits, when present, may also take part in 

 supporting the body, but are usually rudimentary, placed behind, 

 and do not reach the ground ; they may be reduced to the remains 

 of their metatarsals (metacarpals), and not be visible as external 

 digits; this is the case with both of them in Anoplotherium and with 

 the external one in the posterior three-toed limb of Dicotyles. 



The animals belonging to this order may be arranged in two 

 series : the Pachydermata and the Ruminantia. The Artiodactyla 

 were represented in the older tertiaries by forms, which with 

 the Palceotheridce, and perhaps descended from the same source as 

 the latter, were the forerunners of the Suidse and the Ruminants. 



Sub-order 1. Artiodactyla pachydennata. With complete dentition, 

 always with canine teeth and simple stomach. The metatarsal 

 bones of the middle digits are never ankylosed. 



Fam. Anoplothe'ridae. Dentition with all three kinds of teeth which are 

 arranged in a continuous row (i.e., without diastema). AnoplotTieritim com- 

 mune Guv. Fossil. 



Fam. Suidae * (Setigera). With close covering of bristles, and a short 

 proboscis-like snout. The dentition (fig. 692) includes all the kinds of teeth, 

 but the rows of teeth are not perfectly continuous. The 4 6 incisors are 

 placed in an obliquely horizontal position, and fall out in old age. Canines 

 usually nmch elongated and triangular, and in the male as powerful weapons 

 (tusks). There are 6 7 grinders with folded enamel in each jaw (on each 

 side). Only the two middle digits rest on the ground, while the smaller external 



* Herm. v. Nathusius, " Vorstudien fur Geschichte und Zucht der Hausthiere, 

 2tinachst am Schweineschadel," Berlin, 1864 ; and " Die Racen des Schweines," 

 1860. 



