Many deviations in the line of flight of hoofs and in the manner in which they are set to the ground occur; for example, horses heavily burdened or pulling heavy loads, and, therefore, not having free use of their limbs, project their limbs irregularly and meet the ground first with the toe; however, careful observation will detect the presence of one or the other of these lines of flight of the foot. Irregular carriage of the feet renders a horse unsuitable for general purposes only when it is very pronounced, in which case certain troublesome conditions, such as interfering and disease of joints, are of frequent occurrence. D. The Influence of Weight in the Shoe or Otherwise Attached to the Hoof, in Altering the Flight of the Hoof. There is nothing mysterious in the effect of weight upon the flight of the feet. On the contrary, the lines of flight are determined (as shown in pages 72-74, Figs. 71-76), _first_, by the relation of the transverse axes of the hinge-joints of the leg and foot to the line of progression (median line); _second_, by the length and obliquity of the hoof and pastern; _third_, by the height and length of stride which is natural to each individual. _Weight induces higher action and a longer stride._ Inertia increases with the weight. A heavy shoe cannot be snatched from the ground as quickly as a light one, but when moving forward at a given velocity its greater momentum (momentum = mass (wt) × velocity: m = wt × v) carries the foot farther forward then does the lighter shoe. Thus, the heavier shoe, or weight attached to the hoof, lengthens the stride at both ends. The farther from the centre of rotation of the scapula the weight is placed, _i.e._, the nearer to the toe it is placed, the greater the muscular effort required to start it and to stop it. _Height of action_, though largely the result of breeding, temperament, and the exhilaration that accompanies perfect health and entire absence of muscular fatigue, is to a certain extent influenced by the _inclination of the pastern and toe to the cannon_. _The acute-angled foot_, in the folding of the leg during the first half of the stride, moves through a longer arc of a circle whose centre is the fetlock joint than does the normal or the upright foot; rises more rapidly and to a higher point. (See Fig. 76, _B_.) When the momentum of a foot moving rapidly and abruptly upward is increased by weight the result is extreme and even exaggerated flexion of all joints of the leg, and by allowing the hoof to grow long the flexion is still further increased. In the show ring, harness horses with fair natural action may be made to “climb” by shoes weighing from thirty to sixty ounces upon hoofs an inch or more longer than normal. The leverage of a heavy shoe on a long hoof is excessive, fatiguing and most injurious to ligament, tendon and muscle. The action, while high, is _labored_, _pounding_ and _altogether inelegant_. [Illustration: FIG. 77.