Development of the facial midline.

Abstract

"Intellectual excellence lies in having faith in the observation of apparently nontranscendental and unimportant facts. To observe an anatomic element calmly, with an open, analytical spirit, and with spiritual freedom, can lead to an explosive vortex of new knowledge."-Miguel Orticochea, M.D.(1) Traditional descriptive embryology based upon the interaction of frontonasal, lateral nasal, and medial nasal prominences is incapable of explaining the three-dimensional development of the facial midline. The internal structure of the nose and that of the oronasal midline can best be explained by the presence of paired A fields originating from the prechordal mesendoderm, associated with the nasal and optic placodes, supplied by the internal carotid artery, and sharing a common genetic coding with the prosomeres of the forebrain. Mesial drift of these fields leads to fusion of their medial walls; this in turn provides bilateral functional matrics within which form the orbits ethmoids, lacrimals, turbinates, premaxillae, vomerine bones, and the cartilages of the nose. This two-part paper reports six lines of evidence supporting the field theory model of facial development: (1) An apparent watershed exists in the midline of the base between the territories of the internal and external carotid systems. Isolation of the ICA in injected fetal specimens confirmed that the demarcation was distinct and restricted to the embryonic nasal capsule. (2) Field theory explains the developmental anatomy of the contents of the nasal capsule. (3) The neuromeric model of CNS development provides a genetic basis for the anatomy and behavior of fields. (4) Mutants for the Dlx5 gene demonstrate A field deletion patterns. These experiments relate the nasal placode to the structures of the A fields. (5) Separate regions of the original nasal placodes give rise to neurons, which are dedicated to separate sensory and endocrine systems. The A fields constitute the pathways by which these neurons reach the brain. (6) Non-cleft lip-related cleft palate, holoprosencephaly, and the Kallmann syndrome are clinical models that demonstrate the effects of anatomic disturbances within the A fields.