Exactly. Embryology is fascinating in the way many structures are formed. It has been so long since I studied it that I can't describe the steps in which the tube that is the intestinal tract which is I guess endoderm,with a bind end, meets the skin, which is ectoderm, and for quite a while the opening is closed by a layer of both, then a rim forms, and the opening is formed. We are strangely and wonderfully made. I'd be surprised if there were any pictures of this on the Internet, but I'll look.