Internal acoustic meatus

Recommended video: Temporal bone [13:04]

Structure and landmarks of the temporal bone.

The internal acoustic meatus, also known as the internal auditory canal or internal auditory meatus, is a narrow canal passing through the petrous part of the temporal bone. It is approximately 1 cm in length and its internal opening is in the posteromedial part of the bone, within the posterior cranial fossa. At the lateral boundary of the internal acoustic meatus is the fundus, where a thin vertical plate of bone separates the meatus from the cochlea and vestibule of the inner ear. Here, a horizontal crest of bone, the falciform crest, divides the meatus into superior and inferior sections. 

The internal acoustic meatus gives passage for the facial nerve (CN VII), the vestibulocochlear nerve (CN VIII), as well as the labyrinthine artery and veins. It also contains the vestibular ganglion. The facial nerve and the superior vestibular nerve (of CN VIII) pass through openings in the superior portion of the fundus, while the cochlear and inferior vestibular nerves (of CN VIII) pass through openings in the inferior portion of the fundus.