synovial tendon sheath, one of the many membranous channels or tubes enclosing various tendons that glide through fibrous and bony tunnels in the body, such as those under the flexor retinaculum of the wrist. One layer of the synovial sheath lines the tunnel, and the other covers the tendon. The sheath secretes synovial fluid, which lubricates the tendon. Compare synovial bursa, synovial membrane.
