What part of the foot comes first to the ground? Many different answers have been given to this question. It has been said by some that the toe first touches the ground, by others that the foot is laid flat down, and by a few that the heel is the first part to come in contact with the ground. Fortunately it is not now necessary to argue this question on a purely theoretical basis. Instantaneous photography has shown that on level ground, at all paces, the horse touches the ground first with the heel. This fact gives significance to the structural differences we find between the front and back portions of the foot. At the back part of the foot we have the wall thinner than elsewhere, we have the moveable and elastic frog, the lateral cartilages, and the frog-pad. We have in fact a whole series of soft and elastic structures so arranged as to provide a mechanism best adapted to meet shock and to avoid concussion. Whilst drawing heavy loads, or ascending or descending hills, the horse may vary his action to suit the circumstances, and then we have the exception which proves the rule--then we have sometimes the heel, sometimes the toe brought first to the ground.
At the time when the foot first touches the ground, the leg is extended forward and the pastern is in the same oblique position to the shank as when a horse is standing. This obliquity of the pastern is another safeguard against concussion, and it renders impossible the first contact with the ground at any point other than at the heel. As the leg becomes straightened, the weight of the body is imposed upon the foot, but the greatest strain arrives just before the toe leaves the ground, for then there is not only weight to sustain, but the friction to be borne which results from the toe being the fulcrum upon which falls the whole effect of the muscular effort necessary to raise and carry forward the body of the animal. The front part of the foot is structurally well adapted for its use. It presents the thickest and strongest part of the horny covering, and, as an inside basis, it has the unyielding coffin bone. Thus we have at the toe strength and rigidity--at the heels strength and elasticity.
Another important point in the action of the foot is implied by the question--does it expand when weight is thrown on it? The principles of horse-shoeing require that this question should be answered. There are those who say that the foot does not alternately expand and retract as weight is placed upon or removed from it. There are others who assert that the expansion of the foot is an important natural function that must be provided for in any system of shoeing. It is agreed by most observers that at the upper border of the hoof, more particularly at the heels, expansion does occur. It is when we come to the lower border of the foot that the statements are most conflicting. Ordinary measurements taken at this part with calipers or by tracings on paper of the foot when raised from the ground and when resting upon it, show no variations in the width of the foot. These methods of measurement are not sufficiently delicate to be trustworthy. Experimentalists in Germany and in this country have recently used an apparatus by which the slightest variations are detected by electrical contact, and the results are very interesting. These experiments show that in a well-formed, healthy foot the hoof throughout its posterior two-thirds does expand to pressure, and perhaps that the arch of the sole is slightly flattened. This expansion is, however, comparatively slight--about equal to the thickness of a sheet of writing paper--and may practically be disregarded in considering the best methods of shoeing sound feet.