Middle cranial fossa, trigeminal nerve, and cavernous sinus. The cerebrum has been dissected away to expose the brainstem and cerebellum in situ. 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) nerve leaves the ventral midbrain, passes through the interpeduncular fossa, and penetrates the dura between the anterior and posterior petroclinoid ligaments lateral to and in front of the posterior clinoid process. The right trochlear (CNIV) nerve is seen leaving the dorsal surface of the midbrain and curving around the cerebral peduncle 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 middle cranial fossa is the lateral depression between the lesser wing of the sphenoid and petrous portion of the temporal bone. 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. The greater superficial petrosal nerve, a branch of the facial nerve, can be seen leaving its hiatus on the anterior surface of the petrous bone. It passes deep to the mandibular nerve toward the foramen lacerum and pterygoid canal to unite with the deep petrosal nerve to form Vidian nerve. A window has been drilled in the roof of the internal auditory canal to expose the facial nerve. The middle meningeal artery is shown emerging through the foramen spinosum. The tentorium has been incised to expose part of the rostral cerebellum. This surface 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 superior petrosal sinus has been exposed in the tentorial attachment to the petrous ridge and drains the cavernous sinus to the transverse sinus. (Image courtesy of PA Rubino)