Superior midline views of the anterior, middle, and posterior fossae. The cerebrum has been dissected away and the brainstem and cerebellum preserved in situ in this specimen. The olfactory bulbs and tracts can be seen emerging from the cribriform plates in the anterior cranial fossa. The anterior petroclinoid folds or ligaments extend from the anterior clinoid process of the lesser wing of sphenoid to the petrous apex of the temporal bone and represent the attached portion of the tentorium cerebelli (the posterior petroclinoid folds/ligaments are its free edge and extend from a posterior clinoid process to the ipsilateral petrous apex). 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 covering the cerebellum. 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 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. The left trochlear nerve (CNIV) is shown emerging from the dorsal aspect of the midbrain. It wraps around the midbrain and penetrates the dura just below the free border of the tentorium cerebelli. Here, it courses within the lateral wall of the cavernous sinus inferior to the oculomotor nerve and superior to the ophthalmic nerve. All three nerves enter the orbit through the superior orbital fissure. 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. The anterior intercavernous sinus can be seen in the anterior part of the diaphragma sellae and connects the right and left cavernous sinuses. Also 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. On the right side, the ophthalmic artery is shown arising from the internal carotid artery and entering the optic canal. The trigeminal nerve leaves the anterolateral pons as a larger sensory root (portio major) and a smaller motor root (portio minor). The motor root passes beneath the trigeminal ganglion and through the foramen ovale to join the mandibular nerve. The trigeminal nerve passes over the petrous apex and expands as the trigeminal (Gasserian) ganglion in Meckel's cave. The ganglion gives rise to its three divisions: ophthalmic (CNV1), maxillary (CNV2), and mandibular (CNV3) that course toward their openings of exit; superior orbital fissure, foramen rotundum, and foramen ovale, respectively. The middle meningeal artery can be seen emerging through foramen spinosum. On the right side the abducens nerve passes deep to the trigeminal 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 where it courses on the lateral surface of the cavernous segment of the internal carotid artery. The petrolingual ligament extends from the petrous apex to the lingula of the sphenoid bone and its superior margin marks the junction between the cavernous and lacerum segments of the artery. The rostral surface of the cerebellum is supplied by the medial and lateral branches of the superior cerebellar arteries that course posteriorly in the pontomesencephalic sulcus above the superior cerebellar peduncles before ramifying. The venous drainage of the cerebellopontine angle is into the superior petrosal veins, which are tributary to the superior petrosal sinus. The superior petrosal sinus is contained within the tentorial attachment to the petrous ridge and drains the cavernous sinus to the transverse-sigmoid sinus junction. (Image courtesy of AL Rhoton, Jr.)