438 APPLIED BIOLOGY 



the inner side (thumb) being absent, the two outer toes (II 

 and V) are short and do not touch the ground, while the 

 third and fourth are the toes upon which the animal walks. 

 In deer the two outer toes (II and V) are short and in 

 some species absent. In camels and giraffes there are 

 two toes on a foot, the third and fourth, the outer ones 

 (II and V) being absent. In sheep, goats, antelopes, and 

 cattle, the useful toes are the third and fourth, and the 

 outer ones (II and V) are often represented by small hoofs. 



The animals mentioned above, except elephant, are even- 

 toed, i.e., with two or four useful toes on a foot. Other 

 hoofed-mammals are odd-toed, with five, three, or one. 



The elephant has five toes, the rhinoceros three (some spe- 

 cies with four on front feet), the tapir three on hind feet and 

 four on fore feet, and the existing horses have one toe. The 

 three toes on a tapir or rhinoceros foot correspond to second, 

 third, and fourth of an elephant. The fourth toe on a tapir's 

 front foot is the fifth. The one toe or hoof of the existing 

 horses is the third, that is, two toes on either side have dis- 

 appeared from the typical five-toed foot. 



Along with the reduction of toes from five to three, two, 

 or even one, there have been changes in the bones which 

 connect toes to the legs. 



Reduction in the number of toes is well shown by the 

 geological history of the horse, as shown by fossils now ex- 

 hibited in the great museums. Figure 148 shows a series of 

 such fossil feet from a four-toed horse of Eocene times down 

 to the present one-toed type. A five-toed horse-like animal 

 has not yet been found. It should be noted that, as the 

 middle or third toes became the useful ones, the reduced toes 

 were left as small bones at the sides. In existing horses 

 there are two " splint bones " which represent the degen- 

 erated second and fourth toes of the three-toed horses. 



These modifications of the feet of hoofed animals appear to 

 be adaptations to different habits of life. The horse is 



