All bodies which under pressure or traction change their form, but return again to their original shape as soon as the pressure or traction ceases, are called elastic or springy. Nearly all parts of the horse’s foot, except the bones, possess more or less elasticity. The lateral cartilages and the plantar cushion are elastic to a high degree, but the coronary band, the laminæ, the articular cartilage, and the horny box or hoof are less elastic. This property or characteristic is possessed by the respective parts of the foot in accordance with their function, location, and structure.
Fig. 21.
Plantar cushion seen from below: a, base or bulb of the plantar cushion; b, summit; c, median lacuna or cleft in which lies the “frog-stay” of the horny frog.
Fig. 22.
Plantar cushion seen from above: a, base (bulbs) of same; b, summit; c, suspensory ligament of plantar cushion; d, place at which the elastic ligament connecting the os suffraginis and the lateral cartilage unites with the plantar cushion.
The two lateral cartilages ([Figs. 19, C] and [20, b]) are irregular, quadrangular plates, attached to the wings of the os pedis, and extending so far upward and backward that one can feel them yield to pressure on the skin above the coronet, and can thus test their elasticity. The perforans tendon and the plantar cushion lie between the lateral cartilages, and on the sides and behind are partially enclosed by them. The internal concave surface of the lateral cartilage ([Fig. 20]) is attached to the plantar cushion, the os pedis, and the navicular bone, and, like the external, slightly convex surface, is covered with many blood-vessels (veins) [Fig. 25, B].
Fig. 23.
