The horse is generally described as a remarkable animal, at once exhibiting perfection of mechanism, complete balance of form, as well as beauty of outline. Professor Sir W. Flower lays great stress on the specialization of the horse, that is, the modification of its structure from the average type of quadruped to meet some special requirements. The horse is a favourite subject for the evolutionist, as illustrating probably more satisfactorily than any other mammal the truth of the doctrine of evolution. In particular, various rudimentary and apparently useless parts are met with in the horse which correspond to fully-developed structures found in other mammals. Such rudimentary structures in animals may either be in process of growth or they may have the character of vestigial remains; that is, they may be structures that have degenerated from a former more perfect state of development and are now only vestiges of what they once were. In the horse most of the rudimentary structures and parts appear to be in the vestigial condition, and the discoveries in the geological history of the horse all point to that conclusion.
Although the horse as it now exists may be looked upon as one of the most recent among animals from the point of view of the geologist and naturalist, from the historian's point of view its antiquity is considerable, since it can be traced back almost to the beginning of the historic period. According to Dr. George Fleming, the horse was domesticated among the Egyptians nearly 2000 years B.C. The Persians, Greeks, and Romans used the horse for ordinary work and in war not only to carry the riders, but also for the even more useful purpose of being harnessed to chariots, with which the armed warriors were accustomed to attack. (See the chapters on the History of the Horse.) That the horse is specially adapted for the purpose of supporting weight and also for rapid movement, we might conclude even from an inspection of the skeleton, which with all its delicacy of outline is so adjusted, that great strength is combined with perfect elasticity.