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Embryological studies on the mouse indicate that, contrary to the classical concept, all the enteric ganglia are from a single, vagal, neural crest source. The immature ganglion cells first enter the gut by way of the newly formed vagal outgrowth at 10 days gestation. The neuroblasts then migrate down the gut in a cranio-caudal direction, being replaced by more neuroblasts from the vagus. By 15 days 12 h the process is complete and ganglion cells are present throughout the gut. The process is continuous and there is no evidence of a lumbosacral origin for any of the intramural ganglia.

In mice which develop aganglionic megacolon the process is basically the same except that the neuroblasts appear to migrate at a slower rate than normal. The result is that the migration of the neuroblasts and the elongation of the gut are out of phase so the migrating neuroblasts cannot reach the end of the gut, despite the …