[New concepts of the biology of human cephalic development. Observations and hypotheses].
Morphological dynamics controlling vertebrate embryo development, which takes place in flotation in a liquid medium, leads to the hypothesis that the pentameric symmetry of echinodermes, ancestors of the vertebrates, is conserved during evolution. This embryogenesis consists of morphological repetitions: synchronous growth of five expansions specialized in exploration and spatial deplacements (head and four limbs); each of these five expansions consists of five buds or five radii (facial buds, fingers and toes). Homomorphism of the mouth, of the hands, and of the feet--which are capture catastrophes over the environment, installed early during development--allows later functional and sensory connections. These morphological repetitions are also demonstrated by the association of facial, hand, and foot buds, malformations for which a topological correspondence can be shown. During vertebrate morphogenesis by flotation in a liquid medium, other phenomena take place. For instance, the palate is formed anteriorly by a triple junction resulting from the fusion of its three constitutive buds.
D000818:Animals; D001921:Brain / Q000196:embryology; D004447:Echinodermata; D005528:Foot / Q000196:embryology; D006225:Hand / Q000196:embryology; D006257:Head / Q000196:embryology*; D006801:Humans; D009055:Mouth / Q000196:embryology
Concepts nouveaux de la biologie du développement céphalique humain. Observations et hypothèses.