A thin, loose vascular connective tissue that makes up the membranes surrounding joints and the sheaths protecting tendons (particularly flexor tendons in the hands and feet) where they pass over bony prominences. Synovial tissue contains synovial cells, which secrete a viscous liquid called synovial fluid; this liquid contains protein and hyaluronic acid and serves as a lubricant and nutrient for the joint cartilage surfaces[BTO]. Synovial tissue can be found in tendons (tissues that connect muscle to bone), bursae (fluid-filled, cushioning sacs found in spaces between tendons, ligaments, and bones), and the cavity (hollow enclosed area) that separates the bones of a freely movable joint, such as the knee or elbow[BTO]. [ http://www.britannica.com/EBchecked/topic/578563/synovial-tissue BTO:0001338 ]