Figure 2.

Comparison of the morphogenesis of the upper lip (A-C) with that of the palate (D-F). After the bilateral maxillary processes (max) fuse externally with the inter-maxillary segment, the resulting epithelial seam (arrow, B) gives rise to mesenchyme (arrowhead, C) to produce a confluent lip. At a later time, the palatal shelves arising internally from the maxillary processes fuse with each other (arrows, D) and with the nasal septum (ns) above them, creating an epithelial seam that transforms to mesenchyme (arrowheads, E) to produce the confluent palate (arrowheads, F). p, sloughed periderm cells. Reprinted with permission.[44]