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
Os trigonum is which type of epiphysis ? 
Select and explain. 
A. Aberrant, B. Pressure, C. Atavistic, D. Traction
C: Atavistic
Answer: C: Atavistic 
Explanation: C i.e. Atavistic