This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Ear, Subject name: ENT
Crus commune is a part of: 
Select and explain. 
A. Cochlea, B. Middle ear, C. Semicircular canal, D. Vestibule
C: Semicircular canal
Answer: C: Semicircular canal 
Explanation: (c) Semicircular canal(Ref Shambaugh, 6th ed., page 42)The posterior and superior semicircular canals fuse together to form a common crus called as "crus commune" which opens into the utricle. Because of this the three semicircular canals open into utricle by five openings instead of six.