The Trigeminal Ganglion and Divisions. A, The right temporal lobe has been removed to expose the middle fossa dura. B, The dura propria of the middle fossa dura has peeled off to the posterior direction from the middle fossa floor. The trigeminal nerve has visualized. C, Oblique coronal section along the line between the porous trigeminus and the foramen ovale (used with permission from Mayfield Clinic). At the anterior margin of the trigeminal ganglion, the dorsolateral and ventromedial walls of Meckel’s cave become an epineural sheath of each division of trigeminal nerve. The contents of the Meckel’s cave are the sensory and motor roots of the trigeminal nerve, trigeminal ganglion, and arachnoid layer. D, The endosteal incision near the foramen ovale leads to cleavage plane between the outer layer (dura propria of middle fossa, meningeal layer) and inner layer (epineural sheath of the mandibular nerve) (used with permission from Mayfield Clinic). E, The anterior portion of the trigeminal ganglion tightly adheres to the overlying arachnoid and dura propria of Meckel’s cave without any potential subarachnoid space. The arachnoid layer has been easily removed from the posterior portion of the trigeminal ganglion due to actual subarachnoid space. F, Superior view of the right temporal bone. The bone on the middle fossa floor has been removed laterally to show the petrous segment of the carotid artery, the Eustachian tube, the tensor tympani muscle, and geniculate ganglion of the facial nerve. The greater superficial petrosal nerve is separated from the horizontal segment of the petrous internal carotid artery. It passes under V3 and joins the deep petrosal nerve from the sympathetic carotid plexus to become the vidian nerve in the vidian canal. (Images courtesy of AL Rhoton, Jr.)