The lip and primary palate begin to develop at four to five weeks gestational age. The two medial nasal swellings and the maxillary swellings fuse to form the upper lip. The nasal swellings merge at deeper levels also and form the intermaxillary segment, which becomes the triangular primary palate, so embryologically, clefts of the lip are almost invariably associated with clefts of the primary palate.
The secondary palate develops at approximately nine weeks developmental age. It is formed by medial growth of the palatal shelves of the maxilla, which normally fuse together and with the nasal septum as the tongue is pushed down during development. So, the pathogenesis of secondary cleft palate is failure of this fusion to occur.
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