The blood vessels and nerves of the vincula in the human hand were studied by anatomical dissection, serial histological section, and angiography. The segmental blood supply of the flexor tendon through the vincula was seen to come from constant branches of the digital vessels that pierce the fibrous sheath proximal to both the proximal and distal interphalangeal joints. These were traced with their accompanying nerves into the flexor tendons. Communication between the interosseous circulation and that of the tendons was demonstrated. The clinical implication of these findings and their application to tendon surgery are discussed.