This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Anatomy
Which structure does NOT form pa of the boundary defining the trigone of the bladder? 
Select and explain. 
A. Interureteric crest, B. Left Ureteric Orifice, C. Right Ureteric Orifice, D. Urachus
D: Urachus
Answer: D: Urachus 
Explanation: The trigone of the bladder is bounded by the openings of the left and right ureteric orifices superolaterally, the interureteric crest between the openings of the ureters and the internal urethral orifice inferiorly. The urachus is the structure that joins the apex of the fetal bladder to the umbilicus. After bih, it becomes the median umbilical ligament.