flexor tendon in its passage over the navicular bone and at its insertion into the os pedis. This function was pointed out by Lafosse in 1754: 'The frog serves as a cushion to the tendon of Achilles . . . it is composed of soft and compact horn . . . of a spongy nature . . . it ought to bear on the ground, as much for the facilité as for the safety of the horse in progression . . . it is the natural point d'appui of the flexor tendon.'
In aiding the movements of the internal parts of the foot, its influence on the lateral expansion of the hoof may be said to be nil, or at any rate extremely trifling; and notwithstanding all that has been imagined and written on the subject of this lateral expansion, it may with confidence be asserted that the lower margin of the horny case, from the toe to the heels, if perhaps not perfectly immovable under all circumstances, after the animal has attained maturity, yet is, in the unmutilated foot, practically so. With the unpared hoof, it may also be asserted that the sole does not descend; the descent of this portion of the foot, and its lateral expansion at the heels to any very appreciable degree, would be incompatible not only with the functions, but also with the anatomy of that organ. The elasticity required to assist in the movements of the horse and to prevent injury, is to be found in other parts of the foot and limb. Such is the result of daily observation, every variety of experiment possible to devise, and a long and attentive study of the anatomy and physiology of this wonderful structure. I have before expressed my opinion that the lateral expansion and sole-descent theory has proved a sad one for the horse, and has caused him years of untold suffering and inconvenience.
