But the horses were not the only group which combined in this way for protection. The third great line of hoofed animals, those which have “cloven” feet of two toes, and which “chew the cud,” have learnt many a lesson of vigilance, fidelity, and affection, by their social habits. Everyone has read of the herds of antelopes or deer, where the sentinels stand faithfully watching while their companions feed, and stamp or whistle when danger is near; while in the herds of wild cattle, not only will the mothers keep a watchful look-out for danger, but the bulls will join to protect the young ones at the risk of their own lives. Mr. Allen relates how, in America, a young bison, which had strayed from the troop and was followed by wolves, was surrounded by a number of old bulls, who, facing about, warily conducted him across the plain till he was safely among the dense mass of buffaloes, which the wolves dared not attack. Now these “ruminant” animals, with complicated stomachs and the power of feeding at long intervals, have spread far and wide over the earth under many different forms, and while some are still very numerous, others are now rare, or almost destroyed. Take, for example, the Camel, the true “child of the desert.” There are no wild camels left now, so long has man conquered and tamed this useful beast of burden. But in past ages vast numbers of camel-like forms lived in North America, which found their way on the one hand to the south, where the Llamas, Alpacas, and Guanacos now feed on the mountains of Peru and Chili, while on the other they travelled over Northern Asia to the deserts of Africa and Arabia, and there became those curious desert-animals which the Arabs used and still use as their beasts of burden. A strange old fellow is the camel, with his two-toed hairy feet, with only nail-hoofs upon them, and his hard pads on his thighs and legs, on which he rests when he lies or kneels. His curious fleshy hump, which is single in the true camel or dromedary and double in the Bactrian camel, serves him as a special provision of fat, and it dwindles when he is short of food, recovering its size and firmness when he is full-fed again; and he is the only cud-chewing animal which has kept his front teeth and defends himself with them, having no horns. [Illustration: Fig. 69. The true Camel (Camelus Dromedarius).] Still more strange in some ways are the giraffes,[169] of which we know very little, except that large forms like them once wandered in Europe.[170] For they, with only the same number of bones as other animals, have these so lengthened out that, as they wander in the tropical forests, their slender legs raise them above all other animals, and their long neck, which nevertheless has only seven joints like all the milk-givers, enables them to reach the high trees, so as to strip off the leaves with their ribbon-like tongues.