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 vertebrae in the neck, thirteen
in the back, seven in the loins, three sacral vertebrae, and twenty
to twenty-two in the tail. In both the dog and the wolf there are