The third cranial nerve has general somatic and visceral efferent - parasympathetic - functions. The former begin with the oculomotor nuclei as a longitudinal group of cells in the periaqueductal grey matter adjacent to the superior colliculi in the midbrain. The fibres run through the medial longitudinal fasciculus and the red nucleus to emerge from the brainstem on the medial aspect of the crus cerebri. The oculomotor nerve runs between the posterior cerebral and superior cerebellar arteries, in proximity to the posterior communicating artery. The IIIrd nerve then passes through the dura and runs in the lateral cavernous sinus; here it lies close to the fourth and sixth nerves, and the ophthalmic branch of the trigeminal. The IIIrd nerve then passes anteriorly through the superior orbital fissure into the orbital cavity to innervate:
NUCLEI MUSCLES
The IIIrd nerve also carries parasympathetic fibres which, together with sympathetic fibres from first thoracic nerve, control pupil size.
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