very long ago, there was no difference in the work done by feet and hands; they were all used for walking, and were thus all, properly speaking, feet. So if we want to understand our feet and hands we must go back to animals which had four feet and no hands, the four feet each having five toes.
Fig. 1 is a drawing of the foot of a crocodile, which is probably not unlike the earliest kind of foot. At the end of the leg bones a and b we see several small bones, and, starting from these, five jointed rays which in the natural position lie flat on the ground. The fore feet and hind feet of the crocodile are almost exactly alike, having the same work to do—i.e., helping the animal to shuffle along the ground. This kind of foot is very well suited for reptiles, such as crocodiles and lizards, which lead a more or less lazy life, merely moving from place to place to find a patch of sunshine to lie in, or a spot which the animals or insects they feed on frequent, and where they can be snapped at easily. Some of these animals, it is true, are capable of darting at times with lightning speed, but this they seem to do by the help of their tails.
The clumsy, shuffling way of walking on the flat of the foot has been given up by most animals, but we still find it in some, such as the bears, which are called plantigrades or sole-walkers because of their flat-soled feet. The feet of the bear are very superior to those of the crocodile, for they are armed with claws which help him to hold prey and to climb trees; but his awkward, shuffling gait shows pretty plainly that the method of moving on the flat sole is not the best possible for running.
A better method of running is found in most of the higher animals, which no longer touch the ground with the sole of the foot, but only with the toes or digits, and are therefore called digitigrades or toe-walkers. Fig. 2 is the foot of a doglike animal (the wolf), and Fig. 3 is that of a catlike animal (the lion), and in both of these we see that the part of the foot which in ourselves we call the heel does not lie on the ground as in the crocodile or the bear, but is raised high above it, so that the animal walks, as we have said, on its toes or digits. The reason why this is a better method of running is that it gives extra length to the leg. A longer leg means a longer stride and greater speed. The wolves, hyenas, and foxes, which are doglike animals, and the lion, leopard, lynx, and all other catlike animals are beasts of prey—that is, they eat other animals which they have to hunt—and all in their turn are liable to be hunted, so they need to be able to run very swiftly. Many of the catlike animals, too, depend, both in attack and defense, quite as much on springing as on running, and so need to be very agile. For both running and springing we ourselves even use our toes and not the soles of our feet,