Central Anatomy of the Third Nerve

Seen here is an axial section of the midbrain at the level of the superior colliculus. The paired nuclei are located ventral to the periaqueductal grey, and the midline central caudal nucleus (CCN) is located between the right and left nuclei. The CCN sends projections to bilateral levator palpebrae muscle for eyelid elevation. The fascicles that exit the IIIrd nuclei carry the fibers destined to innervate the ipsilateral (arranged from medial to lateral) pupillary sphincter (P), inferior rectus (IR), levator palpebrae (LP), medial rectus (MR), superior rectus (SR), and inferior oblique (IO).