The Gross Anatomy of the Oculomotor Nerve of a Human Male

Description

Arising from the ventral midbrain, the oculomotor nerve (cranial nerve III) is traced from the interpeduncular fossa between the cerebral peduncles and then carried anteriorly toward the superior orbital fissure. Superior to its rootlets lie the mammillary bodies and posterior perforated substance, while the nerve’s cisternal segment runs in close proximity to the posterior cerebral artery and superior cerebellar artery. Laterally, its course relates to the uncus and the free edge of the tentorium cerebelli before it approaches the cavernous sinus region on the way to the orbit. Other cranial nerves are rendered for orientation against the brainstem, cerebellum, and inferior cerebrum. Short and direct. Clinically, this is the course you correlate with a classic third nerve palsy pattern: ptosis from levator palpebrae superioris paralysis, a “down and out” eye from unopposed lateral rectus and superior oblique, and mydriasis when parasympathetic fibers are involved. The proximal relationship of CN III to the posterior communicating artery makes this view useful for teaching why a compressive aneurysm often produces a pupil-involving palsy, while microvascular ischemia in diabetes or hypertension may spare the pupil. The illustration also supports discussions of uncal herniation, where the oculomotor nerve can be compressed against the tentorial edge with rapid ipsilateral pupillary dilation. Neuroanatomy and clinical neuroscience courses can use this plate to anchor cranial nerve III’s emergence, cisternal trajectory, and target entry point at the superior orbital fissure in a single frame. It also fits well in neurosurgical and neuroradiology teaching materials that pair vascular lesions (PCom aneurysm, PCA/SCA junction pathology) with exam findings and localization. Anatomical accuracy verified by SciePro's Medical Advisory Board.