Abstract
an assessment of the value of any procedure or method of treatment is dependent upon a proper understanding of the underlying pathology, the natural history of the untreated condition, and an evaluation of what may be attributed to the procedure or treatment under examination. It would therefore seem essential to review briefly the development of clefts of the primary and secondary palates, the effects of these clefts upon subse— quent growth and development of the middle third of the face, and the further effects of surgery in the absence of preliminary orthopaedic treat— ment upon these deformities. Only with such a background can one evaluate the early orthopaedic treatment of the clefts. Formation of Clefts The classical concept of the face developing as a result of fusion of various processes lying free in space (9) has, of course, been discredited. It is now well recognized that what occurs is the migration of mesodermal masses between two continuous sheets of ectoderm covering the face and roof of the oral cavity (23, 21) and that unless the ectoderm is supported and nourished by an intervening layer of mesoderm it will eventually break down and give rise to a cleft (20). The maxillary processes appear during the fourth week as extensions or branches of the mesoderm of the mandibular or first arch, pass around the angles of the primitive mouth, and then across that region which lies below the olfactory placode to produce a solid bar of tissue which is the primitive or primary palate. This primary palate is formed by five weeks and from it develop the central lip and premaxillary com— pleX as far back as the incisive foramen. Consequently, should there be a failure on the part of the mesodermal maxillary processes to penetrate between the layers of ectoderm, this ectoderm will break down and pro— duce a cleft of the primary palate. Such a cleft will be present in the em— bryo by the fifth week.
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