Experimental induction of an incomplete hard-palate cleft in the rat.

Incomplete clefts of the hard palate with soft-palate integrity are among the rarest malformations found in human beings. They appear as oval-shaped openings in the midline of the hard palate and do not extend along its whole length. The amniotic-sac-puncture technique was used to induce such clefts in 10 percent of a group of rat fetuses at day 15.3 of pregnancy. The upper jaws of such fetuses, either 17.3 or 21.3 days old, were examined in the scanning electron microscope and in serial Epon sections. At day 17.3 incomplete clefts of the hard palate were extending toward the soft palate, with the anterior portion of palatal shelves still in the vertical position and with the soft palate already fused. At day 21.3, the incomplete hard-palate clefts were smaller in both extension and width. These observations support the idea that fusion of the soft palate can occur independently of fusion in the hard-palate region.