380 SYSTEMATIC ZOOLOGY 



on the median line of the snout. These horns are made up of 

 very many fiberlike bodies, which have the structure of hairs. 

 Because of its thick skin the rhinoceros was formerly grouped 

 with the hippopotamus and the elephant under the name of 

 Pachydermata (Gr. irax^, thick, and Sepfxa, skin); they are now 

 known to belong to three distinct groups. The fore feet of 

 the rhinoceros bear three or four toes, the hind feet three. 

 It lives in Africa, southeastern Asia, and some of the East 

 Indies. The different species vary much in size, and the horns 

 range from a few centimeters in length to over a meter. In the 

 two-horned species the anterior horn is the longer. 



Suborder 2. Artiodactyla 



The Artiodactyla (Gr. iipTios, even (in number), and Sa'/criAo?, 

 finger or toe), or even-toed Ungulata, are distinguished by having 

 the axis of the foot between the third and fourth digits, which 

 are equally well developed, thus giving rise to the cloven hoof 

 (Fig. 369 c and d). The second and fifth digits may also be 

 present. The teats may be few in number, from two to four, 

 and situated on the posterior portion of the abdomen, or they may 

 be numerous and extend in two lines along the trunk ; the testes 

 always lie in a scrotum. The incisors and canines are often 

 absent from the upper jaw, and the stomach is complex, consist- 

 ing of more than one chamber, and thus differing from the 

 stomach of the preceding suborder, which is always simple. For 

 our purpose the Artiodactyla may be divided into two groups, 

 the first consisting of the hogs and their allies, and the second 

 of the ruminants, or animals which chew their cud. 



In the true hogs the canines are greatly developed, often 

 forming huge tusks ; they include the domestic pig, Sus scrofa 

 domesticus, the wild boar, Si/s scrofa, which extends from India 

 to western Europe and northern Africa, and the hideous wart 

 hogs of Africa. Related to the true pigs are the peccaries, 

 abundant in South America, and extending into Mexico and 

 Texas. In New Guinea and India live the pygmy hogs, genus 

 Porcula, not quite half a meter long, and weighing only four or 

 five kilos. The hippopotami live in Africa and possess two 

 species, of which the larger, Hippopotamus amphibius, may 



