The developing tegmentum vasculosum in the chick cochlea was analyzed by means of scanning electron microscopy. Chick embryos representative of H. L. Hamilton and V. Hamburger stages 35, 37, 41 and 45 were examined in order to study the morphogenesis of the 'lamellae', or folds, of the tegmentum vasculosum and the differentiation of the light and dark cell luminal surfaces.