Synovial membrane is the inner membrane of a joint capsule surrounding a freely movable joint. It is loosely attached to the external fibrous capsule and secretes synovial fluid. Synovial fluid serves to lubricate the joint. The synovial membrane is very extensive. It extends from the margin of the articular surface of the humerus, and lines the coronoid, radial and olecranon fossæ on that bone. Synovial membrane is composed of connective tissue. It secretes synovia, which help lubricate the knee joint. The synovial membrane lines all internal surfaces of the cavity, except for the articular cartilage of the bones.