<prompt> Which structure prevents spread of infection form middle ear to the brain?Tegmen tympaniCribriform plateFundus tympaniPetrous apex  <response>: Tegmen tympani forming the roof of middle ear cavity separates the tympanic cavity from the middle cranial fossa. Boundaries of Middle earRoofTegmental wallFloorJugular wallPosterior wallMastoid walloTegmen tympanic of the petrous pa of the temporal bone.oGreater superficial petrosal nerve.oLesser superficial petrosal nerveoSuperior bulb of internal jugular vein.oTympanic branch of glossopharyngeal nerve.oAditus to mastoid antrum.oPyramidal eminence and stapedius muscle.oFacial nerve veical pa.oChorda tympani nerve entry.Anterior wallCarotid wallLateral wallMedial wall Labyrinthine walloOpening of tensor tympani muscle.oOpening of auditory tube Eustachian tube.oInternal carotid aery.oSympathetic plexus.oCanal of Huguier - Exit of chorda tympanic nerve oFormed by tympanic membrane and bony outer attic wall called scutum oPromontory oFenestra vestibule Oval windowoFenestra cochlea Round window - 2 o TMoFallopian canal - Facial nerve canal prominence oProcess cochleariformis for tendon of tensor tympani Refer: PL Dhingra, Diseases of Ear, Nose Throat, 7th edition, pg no. 6 