[A comparative anatomic contribution to the development of the ossicles and the annular ligament (author's transl)]

The development of ossicles and annular ligament in the rat (Rattus norwegicus L.) is studied by means of light and TE microscopy. Initial stages of ossification are independent of vascularization of the cartilaginous anlage of the ossicles. During endochondral ossification of the incus and the malleus the cells are arranged in zones of growth, hypertrophic cells, and necrotic cells, which is similar to the ossifying epiphysis femoris. The ossification of the stapedial footplate resembles that of the endochondral layer of otic capsule and displays a non-zonal pattern of cellular transformation. Mesenchymal cells are arranged palisade-like in the region of the annular ligament during early stages of development. Later on, their ultrastructure corresponds to fibroblasts. Their number decreases with increasing age. It is discussed whether or not the stapedial footplate belongs embryologically to the labyrinthine block.