The role of the mandible in mouse palatal development revisited.

Growth changes associated with formation of the secondary palate were studied in H-Velaz mouse embryos by morphometric measurement of medial sagittal sections of the heads between days 13 and 15 of embryonic development. Horizontalization of the palatine processes depends primarily on the length of the mandible and is effected by a shift of palatine process material into the supralingual space. The administration of 7.5 mg cortisone acetate im to the female on day 12, of 0.5 mg 6-aminonicotinamide im on day 14, or amniocentesis on day 14 significantly retards growth of the embryo in general and of the mandible in particular without significantly affecting deflexion of the skull base. The different spatial conditions created by disproportion between deflexion of the base and the length of the mandible cause irregularities in the course of horizontalization which lead, as a rule, to cleft palate.