The internal acoustic meatus is divided by a horizontal bony ridge called crista falciformis into two compaments superior and inferior. The upper compament is divided into anterior and posterior poions by a small veical bony crest commonly known as Bill's bar. These bony ridges divide the fundus of internal auditory canal into four quadrants each carrying its own cranial nerve. Anterosuperior with the facial nerveAnteroinferior with the cochlear nervePostero superior and posteroinferior quadrants occupied by superior and inferior vestibular nerves.