Urachus forms -

Ans. is 'a' i.e., Median Umbilical ligament Urachus* Allantois is a vestigial structure and initially bladder is continuous with it. Most of the allantois soon constricts to form a thick fibrous cord called the urachus, which extends from the apex of bladder to the umbilicus. In the adults, the median umbilical ligament represents the urachus. Incomplete closure of urachus results in urachal cyst, sinus or fistula.i) Urachal cyst: Middle part of allantois remains patent (proximal and distal parts are obliterated).ii) Urachal sinus: Patent inferior end of urachus dilate to form urachal sinus.iii) Urachal fistula : Entire urachus remains patent.