In the lacustrine habitations of the stone age in Sweden, and in the _kjoekkenmoedding_ (kitchen remains) of Denmark, of the same epoch, we find the remains of a dog, which, according to Rutymeyer, belongs to a breed which is constant up to its least details, and which is of a light and elegant conformation, of medium size, with a spacious and rounded cranium and a short, blunt muzzle, and a medium sized jaw, the teeth of which form a regular series. This dog, which has been named by geologists _Canis palustris_, fully resembles in size, slenderness of the limbs, and weakness of the muscular insertions, the spaniel, the brach hound, or the griffon. This dog of the stone age is entirely distinct from the wolf and jackal, of which some regard the domestic dog as a descendant, and as it has appeared in Denmark as well as in Sweden, there is no doubt that this species, peculiar to Europe, was subjugated by man and used by him, in the first place, for hunting, and later on for guarding houses and cattle. Later still, in the age of metals, we observe the appearance, both in Denmark and Sweden, of larger and stronger breeds of dogs, having in their jaws the character of mastiffs, and probably introduced by the first emigrants from Asia. There are, moreover, historic proofs that the dogs of the strongest breeds are indigenous to Asia, where we still find the dog of Thibet, the most colossal of all; in fact, in Pliny we read the following narrative: Alexander the Great received from a king of Asia a dog of huge size. He wished to pit it against bears and wild boars, but the dog remained undisturbed and did not even rise, and Alexander had it killed. On hearing of this, the royal donor sent a second dog like the first, along with word that these dogs did not fight so weak animals, but rather the lion and the elephant, and that he had only two of such individuals, and in case that Alexander had this one killed, too, he would no longer find his equal. Alexander matched this dog with a lion and then with an elephant, and he killed them both. Alexander was so afflicted at the premature death of the first dog, that he built a city and temples in honor of the animal. Did the mountainous province of Epirus called Molossia, in ancient Greece, give its name to the _molossi_ that it produced, or did these large dogs give their name to the country? At all events, we know that it was from Epirus that the Romans obtained the molossi which fought wild animals in the circuses, and that from Rome they were introduced into the British islands and have became the present mastiffs.