cannon or cannon bone the area between the knee or hock and the fetlock joint sometimes called the shin of the horse though technically it is the metacarpal iii fetlock sometimes called the ankle of the horse though it is not the same skeletal structure as an ankle in humans known to anatomists as the metacarpophalangeal front or metatarsophalangeal hind joint homologous to the ball of the foot or the metacarpophalangeal joints of the fingers in humans currently these are the worst of both worlds to a layman reader they include the old terms without stating the reason for the misconception that the hoof was a foot therefore the fetlock was an ankle etc they include the new scientific terms without explaining those or the new perception of the rear legs as having to equate them to human ones elongated feet and resting on a toe bone