Developmental changes in the mouse amnion: a SEM study.

Both surfaces of the mouse amnion from 13 to 21 days of gestation were studied by scanning electron microscopy (SEM). The exocoelomic surface is covered by mesenchymal cells and randomly arranged fine fibers at 13 days. By 21 days, these cells are covered by thick fibers frequently arranged in woven pattern. The ectodermal lining of the amniotic cavity at 13 days is characterized by squamous epithelial cells with central patches of short microvilli. An apparent increase in microvilli occurs by 16 days followed by either the loss of microvilli or the formation of microridges by 21 days. These changes may reflect functional changes of the amnion or processes of cell aging.