Superior view into the posterior and middle cranial fossae showing bony landmarks and foramina. The petrous portion of the temporal bone is the boundary separating the middle and posterior fossae. Anterior and lateral to this partition is the squamous portion of the temporal bone, which with the greater wing of the sphenoid bone forms the floor of the middle fossa. In this view, the lower edge of the superior orbital fissure, the foramen rotundum, and the foramen ovale can be seen. In the midline is the body of the sphenoid containing the hypophyseal fossa for the pituitary gland. The dorsum sellae projects from the posterior border of the sphenoid body and, with the basilar part of the occipital bone, forms the clivus. Posterior to the clivus is the foramen magnum, the largest of the cranial foramina. Between the petrous temporal bone and occipital bone is the jugular foramen, which is divided into a pars nervosus and a pars vascularis. Proximal to this opening is the sigmoid groove, which contains the sigmoid venous sinus. (Image courtesy of AL Rhoton, Jr.)