The prehistoric period is characterized by the arrival of the domestic animals in Europe, under the care of man. The dog, swine, horse, horned-sheep, goat, _Bos longifrons_, and the larger ox descended from an ancestor, according to Professor Rütimeyer, of the type of the great Urus, make their appearance together, in association with the remains of man, in the neolithic stage of civilization.[86] Subsequently they spread over the whole of our continent, for the most part under the care of man. The _Bos longifrons_, however, and possibly also the Urus, reverted to feral conditions, just as the horses and oxen, in the Americas and Australia, have done at the present time, and their remains are therefore frequently found in association with animals undoubtedly wild. The domestic horse, the variety of hog descended from the wild boar, and the domestic cattle derived from the Urus, may possibly have passed under the yoke of man, in Europe, since their wild stocks were to be found in that area, both in the prehistoric and pleistocene times. This, however, cannot be affirmed of the swine descended from the southern variety of _Sus Indica_, or of the Celtic shorthorn, of the sheep, or goat, since their wild ancestors were not indigenous in Europe. These animals must have been domesticated in some area outside Europe; and since central Asia is the region where the wild stocks still exist, from which all the domestic animals are descended, it is reasonable to suppose that they were domesticated in that region, and thence introduced, by a race of shepherds and herdsmen, into our quarter of the world. This conclusion is considerably strengthened by the evidence which Professor Heer has advanced, as to the vegetables used by the dwellers on piles in the Swiss lakes, among which some, such as the two kinds of millet, the six-rowed barley (hordeum hexastichon), the Egyptian wheat (triticum turgidum), and a weed (Silene cretica), accidentally brought along with them, are distinctively of southern derivation. The most important wild animals living in this country during the prehistoric period are the urus, the gigantic skulls of which occur in the peat bogs of England and Scotland, the Irish elk, the moose (_Cervus alces_), and the reindeer. The two last are far more abundant in the north than in the south of Britain; their remains have been discovered in the neighbourhood of London, those of both animals at Walthamstow, and those of the latter at Crossness in Kent, on the banks of the Thames. The remains of the bison have not been recorded from any prehistoric deposit in this country. The Irish elk is the only animal which has become extinct; while the moose, or true elk, is the only wild species which has not been proved to have been living in the preceding age. The stag was very abundant.