Superior view of the interior of the skull. The skull floor consists of a series of anterior-to-posterior depressions or fossae: anterior, middle, and posterior. The anterior fossa is formed by the orbital plates of the frontal bone, cribriform plate of the ethmoid, and lesser wings of the sphenoid. It features the crista galli for attachment of the falx cerebri and the cribriform plate containing multiple foramina for the neurofilaments of the olfactory nerve. The middle fossa extends from the lesser wings of the sphenoid to the superior border of the petrous portion of temporal bone and includes the midline body of the sphenoid. Foramina of interest here include the optic canal, superior orbital fissure, foramen rotundum, foramen ovale, foramen spinosum, foramen lacerum, and intracranial opening of the carotid canal. The posterior fossa extends from the superior border of the petrous bone to the transverse groove of the occipital bone. These are the attachment sites of the tentorium cerebelli and contain, respectively, the superior petrosal sinus and transverse sinus. Foramina in the posterior fossa include the internal auditory meatus, jugular foramen, hypoglossal canal, and the foramen magnum. (Image courtesy of AL Rhoton, Jr.)