Superior view of cranial fossae in midline. The cerebrum has been dissected away to expose the brainstem in situ. The left olfactory bulb and tract are shown on the floor of the anterior cranial fossa. Posteriorly (at left border of the image), is the midbrain in axial view. The hyper-pigmented substantia nigra lies within the tegmentum of the midbrain posterior to the cerebral peduncles. The left anterior petroclinoid ligament can be seen extending from the anterior clinoid process of the lesser wing of sphenoid to the petrous apex of the temporal bone and is part of the tentorium cerebelli. 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 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 optic canal on the right has been opened to expose the ophthalmic artery, a branch off the internal carotid, coursing with the nerve to the orbit. The bone of the planum sphenoidale has been removed to expose the sphenoid sinus. The dura mater of the middle cranial fossa has been stripped away to reveal the trigeminal nerve and ganglion, the cavernous sinus, and associated nerves. The oculomotor (CNIII) nerves leave the ventral midbrain, pass through the interpeduncular fossa, and 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. The right trochlear (CNIV) nerve is seen leaving the dorsal surface of the midbrain and curving around the cerebral peduncle between the posterior cerebral and superior cerebellar arteries to gain the lateral wall of the cavernous sinus. It also penetrates the dura between the free and attached edges of the tentorium cerebelli. Both nerves are located in the superior portion of the lateral sinus wall before passing to the orbit through the superior orbital fissure. The trigeminal nerve leaves the lateral surface of the pons and crosses the apex of the petrous bone where it then expands as the trigeminal ganglion. The ganglion lies in Meckel's cave on the trigeminal depression anteromedial to the trigeminal prominence, an elevation on the petrous ridge.  From this sensory ganglion arise its three divisions: ophthalmic (CNV1), maxillary (CNV2), and mandibular (CNV3) coursing toward their openings of exit; superior orbital fissure, foramen rotundum, and foramen ovale, respectively. Deep to the ophthalmic nerve is the abducens nerve. After leaving the pontomedullary sulcus, it ascends on the clivus, penetrates its dura, and passes across the petrous apex below the petrosphenoid ligament (Gruber's ligament; Dorello's canal) to enter the cavernous sinus. Here it courses on the lateral surface of the internal carotid artery before entering the orbit through the superior orbital fissure. (Image courtesy of PA Rubino)