Light micrograph of a human synovial membrane (innermost part of the joint capsule). It delimits the joint cavity of the diarthrosis. A band of synovial cells is concentrated in the vicinity of the lumen of the joint cavity, adopting an appearance reminiscent of a lining epithelium; however, these synovial cells are connective tissue cells that form a discontinuous lining. Deeper is a large space occupied by loose connective tissue with abundant blood vessels containing red cells in the lumen. In the lower frame, a reddish band is observed, rich in collagen fibres that corresponds to the fibrous capsule.