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
Spiral valve is seen in which - 
Select and explain. 
A. Neck of gall bladder, B. Cystic duct, C. Colon, D. Pylorus
B: Cystic duct
Answer: B: Cystic duct 
Explanation: The mucons membrane of the cystic duct forms a series of 5-12 crescentic folds, arranged spirally to form the so called spiral valve of Heister. This is not a true valve.