deprived of the power of resilience or re-action, which the curve between the bar and the crust affords, will speedily fall in.'
Then the functions of the frog are enumerated, and their description is strangely compounded of truth and error. 'The foot is seldom put flush and flat upon the ground, but in a direction downwards, yet somewhat forwards; then the frog evidently gives safety to the tread of the animal, for it, in a manner, ploughs itself into the ground, and prevents the horse from slipping. This is of considerable consequence, when we remember some of the paces of the horse, in which his heels evidently come first to the ground, and in which the danger from slipping would be very great. . . . The frog being placed at and filling the hinder part of the foot, discharges a part of the duty sustained by the crust; for it supports the weight of the animal. It assists, likewise, and that to a material degree, in the expansion of the foot. . . . It is also composed of a substance peculiarly flexible and elastic. What can be so well adapted for the expansion of the foot, when a portion of the weight of the body is thrown on it? How easily will these irregular surfaces yield and spread out, and how readily return again to their natural state! In this view, therefore, the horny frog is a powerful agent in opening the foot; and the diminution of the substance of the frog, and its elevation above the ground, are both the cause and the consequence of contraction: the cause, as being able no longer powerfully to act in expanding the heels; and the consequence, as obeying a law of nature, by which that which no longer discharges its natural function is gradually removed. It is, however, the cover and defence
