This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Abdomen and pelvis, Subject name: Anatomy
Which of the following is called the Mercier's bar in bladder? 
Select and explain. 
A. Mucosa between two ureteric orifices, B. Mucosa between uvula vesicae and ureteric orifice, C. Mucosa between verumontanum and ureteric orifice, D. Mucosa between internal and external urethral orifice
A: Mucosa between two ureteric orifices
Answer: A: Mucosa between two ureteric orifices 
Explanation: The Mercier's bar (interureteric bar/ interureteric ridge) is a curved fold of mucous membrane between the two ureteric orifices inside the bladder. This fold of mucous membrane is formed by the thicknening of the superior border of the trigone muscle. In cystoscopy, the intraureteric ridge appears as a pale band and acts as a guide to the ureteric orifices. The mucosal fold running from the uvula vesicae to the ureteric orifice office is called the Bell's Bar This fold forms the lateral borders of the trigone and contains a band of muscle fibers called the Bell's Muscle. Ref: Gray's Anatomy 41st edition Pgno: 87