The size of other horses, originally larger, has been gradually increased, partly by crossing and partly by a deliberate artificial selection, until a sustained effort, forming part of a general agricultural development, has eventually produced the Clydesdale and the Shire horse of to-day. Increase of size has always, of course, been subject to the limits imposed by the available food-supply, so that while the Clydesdale has been of comparatively old standing in the Lowlands, a much smaller horse held the field until quite recently in the Highlands and in Orkney; while, within the Highland area itself, the so-called “garron,” of Perthshire and the richer parts of Inverness-shire, has for its Island counterpart the smaller, harder, and more active Hebridean pony. But it is impossible to explain these variations of size and type as the direct product of liberal or scanty feeding, although it is no less impossible to disregard the limiting influence of local conditions which prescribe to each district at each period of its development the size and type of horse which can be maintained in vigour within it. Similarly the Shetland pony is not a horse reduced in size by the scarcity of herbage in Shetland. It is the horse whose type and qualities procured its survival in those Shetland conditions which prohibited any considerable increase in its size. These same conditions fixed other characteristics as well. They prescribed and produced a degree of vigour and robustness fitted for the maintenance of life in adversity, and for the performance of feats of labour and endurance apparently impossible for so small a physical frame: the “mettall past belief” is the mark of a survivor in hard circumstances. They gave a great advantage to individuals sheltered by abundant mane and tail, and, above all, by that waterproof double coat of thick fur and long hair which alone can maintain warmth in wind and rain and mist. They favoured that docility and sweetness of temper which make the Shetland pony more truly domestic than any other horse, because they made it essential that the pony should live in intimate dependence on its owner; and these qualities of disposition find their expression in the small ear and the large soft full eye which are so characteristic of the breed.