Base of posterior cranium. The occipital bone forms the majority of the posterior cranial fossa. The foramen magnum conveys the spinal cord into the vertebral canal and the vertebral arteries into the cranial cavity. The atlas, cervical vertebra 1, articulates with the skull at the occipital condyles. Hypoglossal canals are located at the anterolateral margin of the foramen magnum and convey the hypoglossal nerve (CN XII). The petrous portion of the temporal bone forms the remainder of the posterior base of the cranium. The carotid canal is located within the petrous bone and transmits the internal carotid artery (ICA). ICA enters the canal, takes a 90 degree turn, and travels anteromedially toward the foramen lacerum. This foramen is a space at the junction of the petrous apex, greater wing of the sphenoid, and lateral edge of the clivus. The floor of this foramen is filled by fibrocartilage. Lateral to the foramen lacerum within the greater wing of sphenoid is the foramen spinosum for the middle meningeal artery and the foramen ovale for the mandibular and lesser petrosal nerves. The jugular foramen is another incomplete opening between the petrous portion of temporal and occipital bones. Jugular foramen conveys the internal jugular vein, inferior petrosal sinus, and cranial nerves IX, X, and XI. (Image courtesy of AL Rhoton, Jr.)