The pastern bone is altogether above the level of the foot, the coronet bone is partially within the hoof, and the joint between it and the pedal bone is quite within. The pedal, often called the coffin bone, ([Fig. 12]) is entirely within the hoof and fills the front part of the horny envelope completely. It is a peculiarly shaped bone, being continued backwards by two projections which follow the course of the wall to a little beyond the quarters of the foot. ([Fig. 13]). From this point to the extremity of the heels the wall is not supported by bone but by strong plates of gristle, which are called the lateral cartilages.
Fig. 13.—Under surface of Pedal Bone.
Fig. 14.—The Lateral Cartilage.
The Lateral Cartilages are situated one on either side of the foot partly within and partly without the hoof. They form the basis upon which the back part of the wall is moulded, and being elastic permit a certain amount of movement in the posterior parts of the foot. ([Fig. 14]). If the coffin bone filled the whole hoof, the foot would be too rigid. With bone at the front portion we have a firm surface for attachment, and with cartilage at the back we have an equally firm attachment, but one that will yield to blows or pressure and thus better protect the internal parts. These cartilages extend above the level of the hoof, and may be easily felt in the living horse at the back part of the coronet. ([Fig. 15]). Between them, and behind the body of the coffin bone is a large space which is filled up by a mass of soft tissue to which various names have been given, such as plantar-cushion, frog-pad, etc.