front of the pedal bone is called the 'sole callus'. A stone bruise affects the sole of the horse's foot. It is often caused by a horse treading on a stone or sharp type of object, landings from high jumps and excessive exposure to snow. These can also occur when horses, particularly baby horses, perform various acrobatic feats (known as horse gymnastics). A major symptom is lameness. The bars Bars are the inward folds of the wall, originating from the heels at an abrupt angle. The strong structure built up by the extremities of the heel and of the bar is called the 'heel buttress'. The sole between the heel walls and the bars is named the 'seat of corn', and it is a very important landmark used by natural hoof trimmers to evaluate the correct heel height. The bars have a three-layer structure just like the walls (see above). When overgrown, they bend outwards and cover the lower surface of the sole. Internal structures The third phalanx (coffin bone; pedal bone; P3;) is completely (or almost completely) covered by the hoof capsule. It has a crescent shape and a lower cup-like concavity. Its external surface mirrors the wall's shape. The corium, a dermo-epidermal, highly vascularized and innervated layer between the wall and the coffin bone, has a parallel, laminar shape, and is named the laminae. The laminar connection has a key role in the strength and health of the hoof. Beneath the rear part of the sole, there is the digital cushion, which separates the frog and the bulb from underlying tendons, joints, and bones, providing cushioning protection. In foals and yearlings, the digital cushion is composed of fibro-fatty, soft tissue. In the adult horse, it hardens into a fibrocartilaginous tissue when sufficient, consistent concussion stimulates the back of the hoof. Normal transformation of the digital cushion into fibrocartilagineous tissue is now considered a key goal, both for prevention of, and for rehabilitation of recovering cases of navicular syndrome. The flexor tendon lies deeper, just along the posterior surface of the small pastern bone (PII) and navicular bone, and it connects with the posterior surface of P3; the navicular functions as a pulley. The hoof mechanism The horse hoof is not a rigid structure, but fairly elastic and flexible. When loaded, the hoof physiologically changes its shape. In part, this is a result of solar concavity, which has a