Endocranial view of skull base. The anterior cranial fossa is comprised of frontal and ethmoid bones and is bounded posteriorly by the lesser wings of sphenoid. The middle cranial fossa is comprised of the body and greater wings of the sphenoid and the squamous part of the temporal bone and is bounded posteriorly by the petrous portion of temporal bone. The middle cranial fossa contains the optic canal, superior orbital fissure, foramen rotundum, ovale, spinosum, and lacerum. The posterior cranial fossa is bounded anteriorly by the petrous bone and posteriorly by the occipital bone, the principal bone of this fossa. The posterior fossa contains the internal acoustic meatus, foramen magnum, jugular foramen, and hypoglossal canal. The dorsum sellae of the sphenoid and the basilar portion of the occipital combine to form the clivus, the slope of bone anterior to the foramen magnum. The sella turcica is bounded anteriorly by the tuberculum sellae, a ridge of bone posterior to the chiasmatic groove, and the dorsum sellae posteriorly, and contains the pituitary gland. The jugular foramen is partially divided by the intrajugular processes of temporal and occipital bones into two parts: pars nervosa and pars vascularis. The pars nervosa is the smaller anteromedial part of the jugular foramen and transmits the inferior petrosal sinus and the glossopharyngeal nerve. The pars vascularis is the larger posterolateral portion of the foramen for the internal jugular vein and vagus and spinal accessory nerves. (Image courtesy of AL Rhoton, Jr.)