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
Which structure prevents spread of infection form middle ear to brain ? 
Select and explain. 
A. Tegmen tympani, B. Cribriform plate, C. Fundus tympani, D. Petrous apex
A: Tegmen tympani
Answer: A: Tegmen tympani 
Explanation: Ans. is 'a' i.e., Tegmen tympani Tegmen tympani (forming the roof of middle ear cavity) separates the tympanic cavity from middle cranial fossa.