Stepwise Dissection Focusing on the Lower Clivus. G, The right lower clivus has been drilled while preserving the vidian canal, articular facet of the occipital condyle, and anterior edge of the foramen magnum. The triangular area surrounded by the petroclival fissure, jugular foramen, and hypoglossal canal corresponds to the site of the jugular tubercle on the intracranial surface. Cranial nerves IX, X, and XI course just behind the jugular tubercle. H, Enlarged view. The lower clivus has been drilled bilaterally. Opening the lower clival dura exposes the anterior surface of the medulla and the vertebral, posterior inferior cerebellar, and anterior spinal arteries. The glossopharyngeal and vagus nerves arise from the retro-olivary sulcus rostral to and behind the level of origin of the hypoglossal rootlets. The whole cisternal segment of these nerves can be exposed by drilling of the jugular tubercle. The accessory rootlets are hidden by the hypoglossal canals and the vertebral arteries. I, Midsagittal section of another specimen showing the relationship between the posterior nasopharynx and lower clivus. The anterior surface of the clivus leans approximately 45-degree anterior in the view through the nasal cavity. The posterior nasopharyngeal wall has 3 layers: mucosal, fascial, and muscular. The pharyngobasilar fascia and longus capitis muscles are attached to the clivus; the longus colli muscles are attached to the atlas. The rectus capitis anterior muscle is not shown because the muscle is situated lateral to the midline. J, Enlarged view. The pharyngobasilar fascia diminishes in thickness as it descends and gradually blends into the superior pharyngeal constrictor at the level of soft palate. The anterior edge of the pharyngeal tubercle is located at almost the same level as the pontomedullary sulcus. (Images courtesy of AL Rhoton, Jr.)