THE ULTRASTRUCTURE OF EQUINE SYNOVIAL-MEMBRANE

The ultrastructure of synovial membrane was studied in two adult stall ions of the English thorougbred horse. Samples were collected from 2 a stragalar and 2 knee joints of stallions. The equine synovial membrane was composed of two cell. types, A and B, and the synovial matrix whi ch extended into subsynovial tissue. Synoviocytes, located singly, wer e usually covered with synovial matrix; they were in contact with the joint cavity only occasionally. A-cells showed a structure generally s imilar to the mammalian cells of this type but they were flatter and h ad no cytoplasmic projections. The cytoplasm of B-cells was free of se cretory granules and lacked fibrils passing through the plasma membran e. The synovial matrix of the surface layer showed numerous dense bodi es. The occurrence of thick bundles of aperiodic filaments which were several mu m long and 0.2-0.3 mu M thick was an unusual finding.