A microscopic finger-like structure found on the dermis (corium) of the hoof. Papilla are a feature of the dermis of the periople, the coronet, the sole and the frog. The papilla vary in thickness and in length depending on their location; the papilla on the coronary dermis are much longer and thicker than on the perioplic dermis, the sole or the frog. The dermal papilla form the basis of the horn tubules.