1670s, from Latinized form of Greek gastroknemia "calf of the leg," from gaster "belly" (see gastric) + kneme "calf of the leg," from PIE *kone-mo- "shin, leg-bone" (see ham (n.1)). So called for its form (the "protuberant" part of the calf of the leg). Related: Gastrocnemical.[gastrocnemius etymology, gastrocnemius origin, 英语词源]