Malformations of the external auditory meatus and auricle of mouse fetuses caused by maternal hypervitaminosis A were examined histologically, The fetuses were taken from the mothers on day 12, 13, 14 or 18 of pregnancy, following injections of vitamin A on day 8, 10 or 14 of pregnancy. We observed abnormal separation or enlargement of the primitive external auditory meatus due to disturbance of its extension along the tubotympanic recess. The mice injected on day 8 of pregnancy showed marked or moderate malformations; mice injected with vitamin A on day 14 of pregnancy generally showed a lower grade abnormality. The incidence of malformations was greater in mice injected on on day 8.
