M, A suboccipital craniotomy has been completed, the posterior arch and posterior ramus of the transverse process of the atlas removed, and the dural incision has been outlined. The posterior meningeal artery arises before the vertebral artery penetrates the dura. The C1 nerve root adheres to the lower margin of the vertebral artery. N, The dura has been opened and the nerves passing toward the jugular foramen exposed. Bone has been removed above the atlanto-occipital joint to expose the hypoglossal nerve in the hypoglossal canal. The accessory rootlets cross the jugular tubercle on their way to the jugular foramen. (Images courtesy of AL Rhoton, Jr.)