The osseous spiral lamina consists of two plates of bone, and between these are the canals for the transmission of the filaments of the acoustic nerve. On the upper plate of that part of the lamina which is outside the vestibular membrane, the periosteum

Periosteum

Periosteum is a membrane that lines the outer surface of all bones, except at the joints of long bones. Endosteum lines the inner surface of all bones....

 is thickened to form the limbus spiralis (or limbus laminæ spiralis), this ends externally in a concavity, the sulcus spiralis internus

Sulcus spiralis internus

On the upper plate of that part of the lamina which is outside the vestibular membrane, the periosteum is thickened to form the limbus laminæ spiralis, this ends externally in a concavity, the sulcus spiralis internus, which represents, on section, the form of the letter C.-External links:*...

, which represents, on section, the form of the letter C.

External links

• http://www.anatomyatlases.org/MicroscopicAnatomy/Section16/Plate16311.shtml
• http://www.med.uiuc.edu/histo/small/atlas/objects/103.htm