Superior view of interior of posterior half of the skull. Portions of the middle and posterior fossae are in view in this bony specimen. The boundary separating these two fossae is the petrous portion of the temporal bone. The greater wings of the sphenoid contain the foramen rotundum for the maxillary nerve and foramen ovale for the mandibular nerve and lesser petrosal nerve. Between the greater wing and lesser wing is the opening of the superior orbital fissure. The squamous portion of the temporal bone completes the floor of the middle fossa laterally. The body of the sphenoid contains a depression, the hypophyseal fossa, for the pituitary gland. The dorsum sellae and basilar part of the occipital bone form the clivus, the slope of bone anterior to the foramen magnum. On the posterior surface of the petrous bone is the internal acoustic meatus for the facial and vestibulocochlear nerves and labyrinthine artery. The lateral border of the occipital bone contains a groove, the sigmoid groove, for the sigmoid sinus. This groove ends at the jugular foramen, a space between the petrous bone and occipital bone for transmission of the internal jugular vein and cranial nerves IX, X, and XI. The jugular foramen is divided into a pars nervosa and a pars vascularis. Between the margin of the foramen magnum and the jugular foramen is the hypoglossal canal for the hypoglossal nerve. (Image courtesy of AL Rhoton, Jr.)