The narrow anatomic region in equids that lies between the enlargement marking terminus of fetlock joint proximally and enlargement adjacent to hoof distally. In comparative anatomy, correlates with base of fingers and toes in humans. Although common term for pastern is ankle, this is a misnomer. The fetlock joint is the metatarsophalangeal in the rear limb, metacarpophalangeal in forelimb. [M.E. pastron, hobble, fr. Fr. pasture, fr. L. pasco, to pasture]