6 DOGS AND ALL ABOUT THEM
legs. Their howl becomes a business-like bark. They smell at the tails of other dogs and void their urine sideways, and lastly, like our domestic favourites, however refined and gentlemanly in other respects, they cannot be broken of the habit of rolling on carrion or on animals they have killed.
This last habit of the domestic dog is one of the surviving traits of his wild ancestry, which, like his habits of burying bones or superfluous food, and of turning round and round on a carpet as if to make a nest for himself before lying down, go far towards connecting him in direct relationship with the wolf and the jackal.
The great multitude of different breeds of the dog and the vast differences in their size, points, and general appearance are facts which make it difficult to believe that they could have had a common ancestry. One thinks of the difference between the Mastiff and the Japanese Spaniel, the Deerhound and the fashionable Pomeranian, the St. Bernard and the Miniature Black and Tan Terrier, and is perplexed in contemplating the possibility of their having descended from a common progenitor. Yet the disparity is no greater than that between the Shire horse and the Shetland pony, the Shorthorn and the Kerry cattle, or the Patagonian and the Pygmy ; and all dog breeders know how easy it is to produce a variety in type and size by studied selection.
In order properly to understand this question it is necessary first to consider the identity of structure in the wolf and the dog. This identity of structure may best be studied in a comparison of the osseous system, or skeletons, of the two animals, which so closely resemble each other that their transposition would not easily be detected.
The spine of the dog consists of seven vertebra in the neck, thirteen in the back, seven in the loins, three sacral vertebra, and twenty to twenty-two in the tail. In both the dog and the wolf there are thirteen pairs of ribs, nine true and four false. Each has forty-two teeth. They both have five front and four hind toes, while outwardly the common wolf has