The oculomotor nerve, or cranial nerve III, is the third of twelve paired cranial nerves. It is responsible of eyelid and eyeball movement. The cranial nerve III (CN III) originates in the oculomotor nucleus situated in the superior colliculus of the midbrain.
When the oculomotor nerve emerges from the brain, it is invested with a sheath of pia mater, and enclosed in a prolongation from the arachnoid. It passes between the superior cerebellar (below) and posterior cerebral arteries (above), and then pierces the dura mater anterior and lateral to the posterior clinoid process, passing between the free and attached borders of the tentorium cerebelli.
The muscles that the CN III controls are the striated muscle in levator palpebrae superioris of the eyelid and all extraocular muscles of the eyeball, except for the superior oblique muscle and the lateral rectus muscle.