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: ENT
Crus commune is a pa of: 
Select and explain. 
A. Cochlea, B. Middle ear, C. Semi circular canal, D. Vestibule
C: Semi circular canal
Answer: C: Semi circular canal 
Explanation: Semicircular CanalsThere are 3 semicircular canals - the lateral, posterior and superior which lie in a plane of right angles to one anotherEach canal has an ampullated end which opens independently into the vestibule and a non ampullated endThe non-ampullated ends of posterior and superior canals unite to form a common channel called the crus commune.So the three canals open into the vestibule by 5 openings.