Some perforating vein groups important for surgical treatment of venous insufficiency, seen from behind. (Dodd's group are venae comm. fem. med. intermedia, Boyd's are the vv. comm. cruris intermed., and Cockett's group empty into a vein of the vv. tib. post.). The levels of two dorsal perforators are also indicated, the upper communicating with a gastrocnemius vein.