The term spavin is applied to two distinct forms of enlargement of the hock, one being a bony excrescence (bone-spavin), and the other a distension of the joint capsule with fluid (bog-spavin). Spavin is also spoken of as occult when the action declares the hock to be the seat of mischief in the absence of any outward physical change. Bog-spavin is dealt with in the section on Diseases of Joints.