Comparative anatomical study of the synovial membrane in representatives of 4 classes of terrestrial vertebrate

The synovial membrane (SM) of some representatives of four terrestrial vertebrate classes was studied by means of scanning electron microscope (SEM). The figures of SM of the mammals (man, mini-pig), birds (fowl, Gallus domesticus L.), reptiles (lizard, Lacerta viridis Laur. and turtle, Testudo graeca L.) and amphibians (frog, Rana esculanta L.) are documented. The SM of all animal species investigated presents a great locally variable appearance in form and surface arrangement of the living cells. The surface of synoviocytes is mostly very rough, forked, the cells having a plenty of wart-like, spiny-like or leaf-like microvilli, with cytoplasmic projections protruding from cell bodies. The largest possible functional surface of SM in mammals is formed by multiple villi and folds, whereas in other animal classes--by a specific arrangement of the lining cells. Locally variable appearance of synoviocytes from human and rabbit joints was described by Date (1979); we have documented the same in birds, reptiles and amphibians, as well. Three characteristic types of locally variable appearance of the surface lining cells were picked out in representatives of the every animal class cited. These cells correspond to the histological types, classified by Key. Beside these basic types, a number of transitory cells appear, that increase the diversity of the appearance of the lining cells in different regions of the SM. We may conclude that all the synoviocytes present the largest possible functional surface, although their external form differs. Their cytoplasm contains all sorts of organelles necessary for synthesis and secretion of mucopolysaccharides of the synovial liquid, as well as for the resorption and phagocytosis.