Right lateral perspective of structures around the tentorial notch. The cerebrum and cerebellum have been dissected away and the brainstem preserved in situ in this specimen. The anterior petroclinoid ligaments extend from the anterior clinoid process of the lesser wing of sphenoid to the petrous apex of the temporal bone and is an extension of the tentorium cerebelli (the posterior petroclinoid ligaments arise from the medial edges of the tentorial notch). The remainder of the tentorium cerebelli is attached to the superior ridge of the petrous bone and to the transverse groove of the occipital bone. It divides the cranial cavity into supratentorial and infratentorial compartments. The tentorial notch or incisura is a U-shaped space that curves around the junction of the midbrain and pons to accommodate passage of the brainstem into the posterior fossa. The hyper-pigmented substantia nigra lies within the tegmentum of the midbrain posterior to the cerebral peduncles. The oculomotor (CNIII) nerves can be seen leaving the ventral midbrain, passing through the interpeduncular fossa toward the lateral wall of the cavernous sinus. They penetrate the dura between the anterior and posterior petroclinoid ligaments lateral to and in front of the posterior clinoid processes. In their course they pass caudal to the posterior cerebral artery, between this and the superior cerebellar artery, both branches of the midline basilar artery. Ventral to the midbrain is the body of the sphenoid featuring the sella turcica, the midline depression containing the pituitary gland and distal pituitary stalk through the opening of the diaphragma sellae. The sella is bounded anteriorly by the tuberculum sellae and its lateral projections, the anterior clinoid processes, and posteriorly by the dorsum sellae and its posterior clinoid processes. In this view, medial to the anterior clinoid processes are the optic nerves (CNII) emerging from the optic canals and the supraclinoid internal carotid arteries. The middle cranial fossa is the lateral depression between the lesser wing of the sphenoid and petrous portion of the temporal bone. The left olfactory tract can be seen emerging from behind the crista galli in the anterior cranial fossa. (Image courtesy of PA Rubino)