Quarter Crack - Anatomy

Anatomy

The hoof is made up by an outer part, the hoof capsule (composed of various cornified specialised structures) and an inner, living part, containing soft tissues and bone. The cornified material of the hoof capsule is different in structure and properties in different parts. Dorsally, it covers, protects and supports P3 (also known as the coffin bone, pedal bone, PIII). Palmarly/plantarly, it covers and protects specialised soft tissues (tendons, ligaments, fibro-fatty and/or fibrocartilaginous tissues and cartilage). The upper, almost circular limit of the hoof capsule is the coronet (coronary band), having an angle to the ground of roughly similar magnitude in each pair of feet (i.e. fronts and backs). These angles may differ slightly from one horse to another, but not markedly. The walls originate from the coronet band. Walls are longer in the dorsal portion of the hoof (toe), intermediate in length in the lateral portion (quarter) and very short in palmar/plantar portion (heel). Heels are separated by an elastic, resilient structure named the 'frog'. In the palmar/plantar part of the foot, above the heels and the frog, there are two oval bulges named the 'bulbs'.

When viewed from the lower surface, the hoof wall's free margin encircles most of the hoof. The triangular frog occupies the center area. Lateral to the frog are two grooves, deeper in their posterior portion, named 'collateral grooves'. At the heels, the palmar/plantar portion of the walls bend inward sharply, following the external surface of collateral grooves to form the bars. The lower surface of the hoof, from the outer walls and the inner frog and bars, is covered by an exfoliating keratinised material, called the 'sole'.

Just below the coronet, the walls are covered for about an inch by a cornified, opaque 'periople' material. In the palmar/plantar part of the hoof, the periople is thicker and more rubbery over the heels, and it merges with frog material. Not all horses have the same amount of periople. Dry feet tend to lack this substance, which can be substituted with a hoof dressing.

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