Superior view of right petrous portion of temporal bone. Bone has been removed to visualize structures within the middle and inner ears. The ganglion of the trigeminal nerve (CN V) sits within Meckel’s cave at the apex of the petrous portion. Its three branches (V1, ophthalmic; V2, maxillary; and V3, mandibular) exit the skull via the superior orbital fissure, foramen rotundum, and foramen ovale, respectively. The middle meningeal artery emerges through the foramen spinosum. The external auditory canal conveys sound waves that cause vibration, first of the tympanic membrane, and then the auditory ossicles, malleus, incus, and stapes. The stapes attaches to the oval window of the vestibule of the inner ear. The cochlea is a scroll-like structure that contains the sensory receptors for hearing. Three pairs of semicircular canals, superior, posterior, and lateral contain receptors that detect angular acceleration and are oriented at right angles to one another. The facial nerve (CN VII) enters the internal auditory meatus and ends at the geniculate ganglion from which arises the greater petrosal nerve. The main portion of the facial nerve bends posteriorly and continues along the medial wall of the tympanic cavity within the facial canal. The tensor tympani muscle enters the anterior wall of the tympanic cavity. Inferolateral to it courses the lesser petrosal nerve. It leaves through a hiatus and exits the skull via the foramen ovale. It contains preganglionic parasympathetic fibers involved with secretomotor supply to the parotid gland.  (Image courtesy of AL Rhoton, Jr.)