Histologic study of the vestibulocochlear nerve.

The vestibulocochlear nerve was studied histologically in cross section from the brain stem to the lateral fundus of the internal within the posterior cranial fossa. The cochlear fibers were denser and darker than the vestibular. This difference created double staining of the eighth cranial nerve in the posterior cranial fossa. At the porus acusticus, the nerve fibers became myelinated. Myelin appeared on vestibular fibers more medially than on cochlear fibers. A discrete point of vestibular-cochlear separation was consistently identified in the lateral portion of the internal auditory canal near Scarpa's ganglion. These results suggest that the most reliable point for discrimination of cochlear from vestibular nerves occurs inside the internal auditory canal.