Vascular and neuroanatomy of the right cavernous sinus and petrous apex. The motor and sensory roots of the trigeminal nerve cross the apex of the petrous bone to the middle fossa. From the trigeminal ganglion arise the three divisions of this nerve. The ophthalmic and maxillary nerves are sensory only. The mandibular nerve is both motor and sensory and these roots join as they pass through the foramen ovale. Entering the edge of the tentorium cerebelli attachment to the anterior and posterior clinoid processes are the oculomotor and trochlear nerves (the former located superior to the trochlear nerve). Inferior to the trochlear nerve is the ophthalmic nerve. All three of these nerves course within the lateral wall of the cavernous sinus before entering the orbit through the superior orbital fissure, a space between the lesser and greater wings of the sphenoid. The abducens nerve also follows these nerves into the orbit. After leaving the pons, the abducens ascends on the clivus and penetrates the dura. It passes deep to the petrosphenoid ligament (Gruber's ligament) through Dorello's canal to enter the cavernous sinus where it courses along the lateral surface of the cavernous segment of the internal carotid artery. The maxillary nerve is shown entering the foramen rotundum and it courses to the pterygopalatine fossa where it becomes distributed with branches of the maxillary artery. The Vidian nerve also enters the pterygopalatine fossa via the pterygoid or Vidian canal. The greater superficial petrosal nerve is shown leaving its hiatus on the anterior surface of the petrous bone and passing deep to the trigeminal ganglion. Just inferior to this is the lesser petrosal nerve, which courses through the foramen ovale. It carries preganglionic parasympathetic fibers that will synapse in the otic ganglion in the infratemporal fossa. The optic nerve enters the optic canal on the medial aspect of the anterior clinoid process. Several segments of the internal carotid artery are visible, including the petrous, cavernous, clinoid, and ophthalmic or supraclinoid segments. (Image courtesy of AL Rhoton, Jr.)