Oblique View of the Skull Base. The petrous and mastoid parts of the temporal bone articulate posteriorly with the occipital bone to form the lateral part of the anterior wall of the posterior fossa. Medially, the petrous part of the temporal bone articulates along the petroclival fissure with the clival portion of the occipital bone and the body of the sphenoid bone to form the medial part of the anterior wall of the posterior fossa. The jugular foramen is positioned between the occipital and temporal bone at the inferolateral edge of the petroclival fissure. The petrous part of the temporal bone forms the anterior edge, and the condylar part of the occipital bone forms the posterior edge of the jugular foramen. The jugular foramen has three parts: a laterally placed sigmoid part, through which the sigmoid sinus drains; a smaller medial part, the petrosal part, through which the inferior petrosal sinus drains; and an intermediate part, the intrajugular part, through which the glossopharyngeal, vagus, and accessory nerves pass. (Image courtesy of AL Rhoton, Jr.)