400 MAMMALIA 



teeth) while the African form has three toes on its hind feet instead 

 of four. It reaches a height of twelve feet. (Figure 227.) 



Sub-Order Perissodactyla. — Perissodactyla are o^^-/o^(^Ungulata 

 with an uneven number of digits; the axis of symmetry passes 

 through digit three. Premolars and molars are completely folded. 

 Stomach simple; cecum large. Gall bladder absent, teats situated 

 in the groin and placenta diffuse. (Horse, tapir and rhinoceros.) 



The tapijs {Tapiridae), found in tropical America and India, are 

 as old a family as the horses {Equidae). They have four-toed fore 

 feet and three-toed hind feet. The nose and upper lip are elongated 

 into a proboscis. Tapirs are enemies of the cocoa plant. They are 

 hunted for food and for their hides. 



The rhinoceroses have extremely thick skin deposited in folds 

 resembling plates of armor. The East Indian species has one nose 

 horn, and the African white rhinoceros has two. Nose horns, out- 

 growths of skin like whalebone, grow at the base as the tip wears 

 away. They are used as weapons, and powdered for medicines. 

 The rhinoceros injures cane and melon fields, and cacao plantations. 



The horse {Equidae) has a geological record back to the Eocene 

 Epoch when the little Eohippus had four complete toes and the 

 splint of a fifth on its fore feet, while the hind feet had three com- 

 plete toes and a splint of the fifth. It was about the size of a small 

 dog. (See p. 526, The Evolution of the Horse.) 



All our horses have been introduced from the Old World. Wild 

 horses are found at the present time in Asia {Equus heinmonus, the 

 Asiatic Wild Ass; and Equus przewals kit, Przewalsky's Horse) and in 

 Africa (£. asinus, the African Wild Ass; and the Zebras, Equus 

 zebra, burchelli, and Quagga). 



The African Wild Ass has been domesticated and is utilized as 

 our donkey. The White Ass was used in Africa as a means of 

 transportation for the great, centuries ago. Andrews states that the 

 Asiatic Wild Ass is capable of bursts of speed of 60 miles an hour. 



Hybrids. — The " mule," a hybrid between the horse and the ass, 



is an extremely powerful draft animal. Male hybrids are as a rule 



infertile,^ and only a few cases of fertile hinnies ^ have been reported. 



8 Wodsedalek, J. E. 1916. Causes of sterility in the mule. Biol. Bull., vol. 30, 



PP- 1-39. 1916. 



8 Groth, of the Texas A. and M. College, has reported a case of "Old Beck," a 

 fertile mule, who in 1920 produced a daughter, sired by a Jack, and later produced a son 

 sired by a stallion. It is further reported that the horse-like colt has sired a healthy 

 colt, making "Old Beck" a grandmother. 



