<prompt> Anal opening is formed in which week of embryonic development:5th7th10thNone of the above  <response>: The hindgut terminates temporarily at an ectodermal-endodermal membrane, the cloacal membrane. This membrane separates the upper pa of the anal canal, derived from endoderm, from the lower pa, called the proctoderm that is formed by an invagination pit lined by ectoderm. The membrane breaks down in the seventh week to create the opening for the anus. Ref: Langmans embryology 11th edition Chapter 7. 