The petrous portion of the temporal bone or pyramid is pyramidal and is wedged in at the base of the skull between the sphenoid and occipital bones. Directed medially, forward, and a little upward, it presents for examination a base, an apex, three surfaces, and three angles, and contains, in its interior, the essential parts of the organ of hearing. The petrous portion is among the most basal elements of the skull and forms part of the endocranium.[WP,unvetted]. [ http://en.wikipedia.org/wiki/Petrous_part_of_the_temporal_bone ]