Transclival view of internal head structures. Much of the clivus has been removed to expose the pons and medulla and associated arteries, including the vertebral and its posterior inferior cerebellar artery and the basilar artery and its anterior inferior cerebellar artery branches. In the upper midline of the image is the pituitary gland resting in the sella turcica. Lateral to this is the cavernous segment of the internal carotid artery. The ophthalmic artery can be seen within the apex of the orbit along with the optic nerve. Lateral to the petrous segment of the internal carotid artery are the maxillary and mandibular nerves. These can be seen on the left side of the image entering, respectively, the pterygopalatine and infratemporal fossae. The odontoid process or dens (a midline projection of bone from the superior surface of the axis) is exposed following removal of the anterior arch of the atlas. (Image courtesy of AL Rhoton, Jr.)