The osseous spiral lamina is a bony shelf or ledge which projects from the modiolus into the interior of the canal, and, like the canal, takes two-and-three-quarter turns around the modiolus. It reaches about half-way toward the outer wall of the tube, and partially divides its cavity into two passages or scalae, of which the upper is named the scala vestibuli, while the lower is termed the scala tympani. [ http://en.wikipedia.org/wiki/Osseous_spiral_lamina ]