Embryology of Cleft Lip and Palate

The embryologic development of the face has always presented the physician and scientist with an enigmatic mosaic so very different from those satisfying blocks of mesoderm, the somites, which will, with replicating exactitude, form bone, cartilage, muscle, nerve, and blood vessels through the embryo's length. For the sake of simplifying facial development in the embryo, the concepts of developing gill systems and of tentacled, fingerlike processes have been introduced as a sort of literary analogy, much as the reduplication of somites in the human embryo has been compared to the action of the metameres of the earthworm. These homologues have been borrowed from families and orders lower than homo sapiens. The concept of fusing processes has been borrowed from the chick, pig, rabbit, and deer by the Swiss Wilhelm His (1831-1904), and those of the gill or branchial arches from the fish by the Scot Francis Maitland Balfour (1851-1882).