This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nervous System, Subject name: Surgery
Transtentorial uncal herniation compresses which cranial nerve - 
Select and explain. 
A. III, B. IV, C. VI, D. VII
A: III
Answer: A: III 
Explanation: Ans. is 'a' i.e., III * Uncal herniation can compress the third nerve, compromising the parasympathetic supply to the pupil, so that unopposed sympathetic activity produces an enlarged and sluggish pupil, which then, if the compression continues, becomes fixed and dilated.