Endonasal view of the internal carotid arteries, cavernous sinuses, and suprasellar region. Portions of the petrous temporal, sphenoid, and clival bones have also been removed. The petrous, lacerum and cavernous segments of the internal carotid arteries are exposed here. The petrous carotid terminates in the lacerum segment shortly after turning superiorly. The cavernous carotid has a posterior genu in the posterior cavernous sinus, and an anterior genu immediately prior to entering the dural rings and the clinoidal segment. The carotid sympathetic plexus is visible entering the skull base with the internal carotid arteries. The oculomotor (CNIII), trochlear (CNIV), ophthalmic (CNV1), maxillary (CNV2), and abducens (CNVI) nerves traverse the cavernous sinuses; the trochlear nerve is superolateral, between the oculomotor and ophthalmic nerves, and is not visible in this image. Cranial nerves III, IV, VI and V1 enter the orbit anteriorly via the superior orbital fissure. The maxillary nerve exits the skull at the foramen rotundum. Inferomedially, the Vidian canal carries the Vidian nerve (union of the deep petrosal nerve and greater superficial petrosal nerve) anteriorly. Both the maxillary and Vidian nerves enter the pterygopalatine fossa. In the suprasellar region, the optic (CNII) nerves and chiasm can be seen along with the ophthalmic artery. The artery, a branch off the supraclinoid segment of the internal carotid artery, courses with the optic nerve through the optic canal to the orbit. The anterior cerebral arteries, terminal branches of the internal carotid arteries, are visible entering the interhemispheric fissure. (Image courtesy of AL Rhoton, Jr.)