Brainstem anatomy, ventral view. The superior transclival approach provides access to the ventral cerebral peduncles, interpeduncular fossa, mammillary bodies, optic tract, and oculomotor nerve. The middle transclival approach provides access to the ventral pons and abducens nerve, with the trigeminal nerve as the lateral limit. The inferior transclival approach provides access to the ventral medulla or pyramids, superior olive, hypoglossal nerve rootlets at the pre-olivary sulcus, and lower cranial nerves (IX-X-XI) at the post-olivary sulcus. (Image courtesy of JC Fernandez-Miranda)