This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cranial Nerves, Subject name: Anatomy
Which of the following is decussated in superior medullary velum? 
Select and explain. 
A. 3rd nerve, B. 4th nerve, C. 5th nerve, D. 6th nerve
B: 4th nerve
Answer: B: 4th nerve 
Explanation: ANSWER: (B) 4th nerveREF: Neurology: A Queen Square Textbook - page 516Trochlear nucleus (4th nerve) is located in the midline, just ventral to the cerebral aqueduct. Axons leave the nucleus and course dorsally around the aqueduct, decussates within the superior medullary velum and exit from the midbrain on its dorsal surface."Bilateral 4th nerve palsy may be due to a lesion in the superior medullary velum"