[A new concept of normal and pathologic development of the primary palate. 2. The formal genesis of the open and covered cleft lip and jaw].

In part 1 of this work we have shown that in each mammalian embryo the nasal fin represents a masked physiological cleft lip and jaw. In this double-layered "Epithelmauer" the process of epithelium separation along the differentiation-line may undergo various fates: 1. It can completely fail to take place (resulting in total cleft lip and jaw) or can be interrupted (resulting in incomplete cleft). 2. The persisting oral epithelium of the nasal fin may be loosened and moved away with a little temporal retardation. Thereby the potential osteoblasts and myoblasts cannot meet and join at right time and they retract away from the midline epithelial seam. The minimal and subcutaneous cleft lip and the submucous clefts of the jaw and the mesenchymal bridges may result. 3. Only in very rare cases the cleft lip and jaw develop in another way, namely if the underdeveloped facial processes do not meet.