The support afforded by the horny frog and plantar cushion to the flexor tendons is not without its counterpart in other regions of the body. We find cushions of fat, for example, placed in various situations to act as a pad, and particularly in maintaining the structures surrounding joints in close approximation to these, especially in the anterior and posterior extremities; but there the enveloping muscles play the part that ground pressure does on the frog.
It may be noted that the wall or crust of the fore foot is thickest at the front part, or toe, and gradually diminishes in substance, as it does in depth, towards the heels, the inside quarter and heel being the thinnest and straightest, while the outside quarter is stronger, wider, and more circular. The hind foot, on the contrary, is strongest and widest towards the quarters and heels, and is deeper there than the fore one; the frog is also smaller, and the sole more concave.
In the unshod fore foot, a large portion of the plantar surface comes into contact with the ground, even when this is in a hard condition. If we place a fresh hoof that has never been shod—I mean one that has not been trimmed and dressed by the farrier, and that belonged to an animal with no hereditary defect in this respect—on a table, we will find that the crust, bars, and a considerable portion of the posterior part of the frog are on the same plane, and must have sustained wear together. The outer surface of the crust looks shining, tough, and solid; the sole is wonderfully thick, and the horn beneath the flakes, if there are any, is moist, flexible, and easily cut; while the frog, if it be a fore foot, extends well towards the
