[Illustration:  SKELETON OF HORSE OR ASS.
    i, Incisor teeth. g, Grinding teeth, with the gap between the two
    as in all grass-feeders. k, Knee. h, Hock or heel. f, Foot. s,
    Splints or remains of the two lost toes. e, Elbow. w, Wrist. h,
    Hand-bone. t, Middle toe of three joints, 1, 2, 3 forming the
    hoof.]

Meanwhile during these long succeeding ages while the foot was lengthening out into a slender limb the animals became larger, more powerful, and more swift, the neck and head became longer and more graceful, the brain-case larger in front and the teeth decreased in number, so that there is now a large gap between the biting teeth and the grinding teeth of a horse.  Their slender limbs too became more flexible and fit for running and galloping, till we find the whole skeleton the same in shape, though not in size, as in our own horses and asses now.

They did not, however, during all this time remain confined to America, for, from the time when they arrived at an animal called Miohippus, or lesser horse, which came after the Mesohippus and had only three toes on each foot, we find their remains in Europe, where they lived in company with the giraffes, opossums, and monkeys which roamed over these parts in those ancient times.  Then a little later we find them in Africa and India; so that the horse tribe, represented by creatures about as large as donkeys, had spread far and wide over the world.

And now, curiously enough, they began to forsake, or to die out in, the land of their birth.  Why they did so we do not know; but while in the old world as asses, quaggas, and zebras, and probably horses, they flourished in Asia, Europe, and Africa, they certainly died out in America, so that ages afterwards, when that land was discovered, no animal of the horse tribe was found in it.

And the true horse, where did he arise?  Born and bred probably in Central Asia from some animal like the “Kulan,” or the “Kertag,” he proved too useful to savage tribes to be allowed his freedom, and it is doubtful whether in any part of the world he escaped subjection.  In our own country he probably roamed as a wild animal till the savages, who fed upon him, learned in time to put him to work; and when the Romans came they found the Britons with fine and well-trained horses.

Yet though tamed and made to know his master, he has, as we have seen, broken loose again in almost all parts of the world—­in American on the prairies and pampas, in Europe and Asia on the steppes, and in Australia in the bush.  And even in Great Britain, where so few patches of uncultivated land still remain, the young colts of Dartmoor, Exmoor, and Shetland, though born of domesticated mothers, seems to assert their descent from wild and free ancestors as they throw out their heels and toss up their heads with a shrill neigh, and fly against the wind with streaming manes and outstretched tails as the Kulan, the Tarpan, and the Zebra do in the wild desert or grassy plain.