E, The fascia has been removed to expose the occipital artery passing behind the superior oblique and semispinalis. F, The longissimus capitis has been reflected to expose the attachment of the superior and inferior oblique muscles to the C1 transverse process. G, The suboccipital triangle, in the depths of which the vertebral artery courses behind the atlanto-occipital joint and across the posterior arch of C1, is situated in the depths of the area between the superior and inferior oblique and the rectus capitis posterior major. H, The superior oblique muscle has been reflected laterally and the rectus capitis posterior major muscle inferomedially. The floor of the suboccipital triangle is formed by the posterior atlanto-occipital membrane and the posterior arch of the atlas. The vertebral artery and the C1 nerve root, which are surrounded by the vertebral venous plexus, course along the upper surface of the posterior arch of the atlas. I, The muscles forming the margins of the suboccipital triangle have been reflected to expose the vertebral artery ascending through the C1 transverse process and behind the atlanto-occipital joint and the surrounding venous plexus. J, The venous plexus around the vertebral artery has been removed. The vertebral artery gives off muscular branches, passes medially behind the atlanto-occipital joint and above the posterior arch of C1, and turns upward and anterior to penetrate the dura. (Images courtesy of AL Rhoton, Jr.)