Light micrograph of a 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 space occupied by loose connective tissue and developing bone (left) or muscle (right). At top, the transition between synovial membrane and articular cartilage can be seen.