Development of apical ectodermal ridge during early hind limb morphogenesis in tadpoles of Rana tigrina (Daud)

Abstract

The hind-limb buds of the tadpoles of Indian bullfrog, Rana tigrina were investigated for the development of an apical epidermal ridge (AER). At stage 34 when the limb buds are approximately as long as broad, the AER appears as a slight thickening at the apex of the limb bud due to the cells of the basal layer of two layered epidermis becoming columnar. At stage 35, when the limb buds are slightly longer than broad , the AER becomes a three layered prominent conical cap extending over the apex of the limb bud. Its basal layer is columnar. The marginal vein in the mesenchyme is very close to the AER and there seems to be no basal membrane below the ridge. The mesenchymal cells immediately below the epidermis are aligned in a row. From stage 36, when the limb bud has attained maximum length, the AER begins to regress and by stage 38 when digit formation begins, the AER is no more discernible.