The flexor retinaculum in the wrist and palm of the hand consists of a group of heavy connective fibers in the tissues of the wrist. It connects the lateral margin of the radius (shorter forearm bone) with the inside border of the ulna (longer forearm bone) and with certain bones of the wrist. The retinaculum gives off branches of connective tissue to the underlying wrist bones, creating a series of sheath-like compartments through which the tendons of the flexor muscles pass to the wrist and fingers.