The bony part of pharyngotympanic tube is about 12 mm. in length. It begins in the carotid wall of the tympanic cavity, below the septum canalis musculotubarii, and, gradually narrowing, ends at the angle of junction of the squama and the petrous portion of the temporal bone, its extremity presenting a jagged margin which serves for the attachment of the cartilaginous portion. [ http://en.wikipedia.org/wiki/Bony_part_of_pharyngotympanic_tube ]