<prompt> Congenital megacolon develops secondary to failure of -Migration of vagal neural crest cells to gutNeurogenesisDefecation reflexExternal anal sphincter relaxation  <response>: Ans. is a i.e., Migration of vagal neural crest cells to gut Hirschsprungs disease congenital megacolon is characterised by the congenital absence of intramural ganglion cells aganglionosis and the presence of hypertrophic nerves in the distal large bowel. The absence of ganglion cells is due to a failure of migration of vagal neural crest cells into the developing gut. The affected gut is in spasm causing a functional bowel obstruction. 