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Of this nature are also the innumerable varieties of the common sheep, which consist chiefly in differences of their fleeces, as the wool which they produce is an important object of attention. These varieties, although not quite so perceptible, are yet sufficiently marked among horses. In general, the forms of the bones vary little; their connections and articulations, and the forms of the large grinding teeth, never vary at all.

The small size of the tusks in the domestic hog, compared with the wild boar’s, and the junction of its cloven hoofs into one in some races, form the extreme point of the differences which we have produced in the domesticated herbivorous quadrupeds.

The most remarkable effects of the influence of man are manifested in the animal which he has reduced most completely under subjection, the dog,—that species so entirely devoted to ours, that even the individuals of it seem to have sacrificed to us their will, their interest, and inclination. Transported by man into every part of the world, subjected to all the causes capable of influencing their development, regulated in their sexual intercourse by the pleasure of their masters, dogs vary in colour; in the quantity of their hair, which they sometimes even lose altogether, and in its nature; in size, which varies as one to five in the linear dimensions, amounting to more than a hundred fold in bulk; in the form of the ears, nose, and tail; in the proportional length of the legs; in the progressive development of the brain in the domestic varieties, whence results the form of their head, which is sometimes slender, with a lengthened muzzle and flat forehead, and sometimes having a short muzzle and a protuberant forehead; insomuch that the apparent differences between a mastiff and a water-spaniel, and between a greyhound and a pug, are more striking than those that exist between any two species of the same natural genus in a wild state. Finally, and this may be considered as the maximum of variation hitherto known in the animal kingdom, there are races of dogs which have an additional toe on the hind foot, with corresponding tarsal bones; as there are, in the human species, some families that have six fingers on each hand. Yet, in all these varieties, the relations of the bones remain the same, nor does the form of the teeth ever change in any perceptible degree; the only variation in respect to these latter being, that, in some individuals, one additional false grinder appears, sometimes on the one side, and sometimes on the other[82].