33 6 



POPULAR SCIENCE MONTHLY. 



touch the ground, shows very clearly the position assumed by the 

 bones of the foot in these animals. Not only are the heel and the 

 first long joints raised above the ground, as in the dogs and cats, but 

 the two remaining long upper joints join together to form one strong 

 bone (Fig. 4 *), and none of the lower joints of the toes touch the 

 ground. The nails of two toes which form what we call the " hoof " 

 rest upon it, while at a we see all that is left of a third and fourth 

 toe, possessed by the distant ancestors of the bison. 



The chief distinction between the feet of the different nail- 

 walkers is the number of toes whose nails form the hoof. Fig. 5 A 

 shows us that the pig has four toes, but only two touch the ground 

 and make the hoof; the other two are useless, and are gradually be- 

 coming smaller. The rhinoceros (Fig. 5 B) has only three toes, and 

 these are not all equal in length, but all are in use and end in massive 

 hoofs. The cow (Fig. 5 C) has only two toes, the upper joints of 

 which have grown together into one as in Fig. 4 (for the bison is one 

 -of the cows) so as to form a long, strong part of the leg, the two very 



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Fig. 5. 



thick nails making a double hoof. This is what is called in the 

 Bible a " cloven " hoof; it is not, however, as was supposed, a single 

 nail split down, but two distinct nails belonging to two toes. Then, 

 lastly, the horse (Fig. 5 D) has lost all its toes except one, which has 

 become exceedingly thick and strong. The horse on its four feet, 

 each ending in only one toe with its great nail, attains immense 

 speed in running, great length being given to its stride by the length- 



