Spatial relations in the oral cavity of cortisone‐treated mouse fetuses during the time of secondary palate closure

Cortisone has long been used experimentally to induce cleft palate in mice, but the mechanisms by which it causes this effect remain controversial. It has been repeatedly demonstrated that after administration of cortisone the movement of the palatal shelves from a vertical to a horizontal position is delayed. The long‐accepted hypothesis is that during this delay growth of the head continues so that when the palatal shelves finally do become horizontal they are too far apart to meet in the midline and fuse. We found that maternally administered cortisone induced 95% cleft palate in ICR/DUB mouse fetuses observed at days 15–18 of gestation. Observations made on frozen, cryostat‐cut sections of fetal heads during the time of palate closure indicated that shelf elevation in experimental animals was delayed by as much as 12–14 h. However, when the shelves finally reached the horizontal they made contact with both the nasal septum and each other. It seems therefore that cortisone, beside causing delay in self movement, may also interfere with processes that occur subsequent to horizontalization leading to shelf fusion.