View of left posterior petrous portion of temporal bone. Bone has been removed to visualize the three semicircular canals: superior (anterior), posterior, and lateral (horizontal). The arcuate eminence is a visible landmark for indicating the location of the superior semicircular canal. The internal acoustic meatus conveys the facial and vestibulocochlear nerves (CN VII and VIII) and labyrinthine artery. The trigeminal ganglion is located within Meckel's cave overlying the trigeminal impression at the apex of the petrous bone. The superior petrosal sinus is located along the petrous ridge and drains the cavernous sinus into the transverse sinus. Lateral to the internal auditory meatus is a small opening, the vestibular aqueduct. This is a narrow bony canal that contains the endolymphatic duct and sac, thus connecting the endolymphatic space of the inner ear to the posterior wall of the petrous bone. Inferior to the internal auditory meatus is the cochlear canaliculus, a small opening for the cochlear aqueduct. This contains the perilymphatic duct which arises from the scala tympani of the cochlea and drains perilymph into the subarachnoid space in the posterior fossa. The subarcuate fossa is a small triangular depression inferior to the arcuate eminence and superior and lateral to the opening of the internal auditory meatus. It typically receives the subarcuate artery, a small branch of the anterior inferior cerebellar artery.  (Image courtesy of AL Rhoton, Jr.)