embryology
Last reviewed 01/2018
The middle third of the face develops as the result of the migration and fusion of mesodermal folds covered by ectoderm. Unilateral, bilateral or, rarely, median cleft lip is the result of the failure of fusion of the primary palate.
The secondary palate develops from folds on either side of the tongue. These folds rise above the tongue and fuse in the mid-line to form the true palate. A cleft palate occurs when the tissue migration is disorganized or obstructed by the tongue. Rarely, a cleft palate is caused by a small mandible.