The third cranial nerve (AC7) contains so-matomotor and visceromotor (parasympa-thetic) (A8) fibers. It innervates the remain-ing outer eye muscles (E) and, with itsvisceromotor portion, the intra-ocularmuscles. The fibers exit from the floor of theinterpeduncular fossa at the medial margin of the cerebral peduncle in the oculomotorsulcus. Laterally to the sella turcica, they penetrate the dura mater, run through the roof and then through the lateral wall of the cavernous sinus, and enter the orbit through the superior orbital fissure. Here, the nerve divides into a superior branch, which supplies the levator muscle of theupper eyelid and the superior rector muscle (E9), and into an inferior branch, which sup-plies the inferior rector muscle (E10), the me-dial rector muscle (E11), and the inferior ob-lique muscle (E12).The somatomotor fibers originate from large multipolar neurons of the nucleus of theoculomotor nerve (AC13), whichlies in the midbrain below the aqueduct at the level of the superior colliculi.
The longitudinally arranged cell groups in-nervate specific muscles. The neurons for the inferior rector muscle (D14) lie dor-solaterally, those for the superior rector muscle (D15) dorsomedially; below them lie the neurons for the inferior oblique muscle (D16), those for the medial rector muscle (D17) ventrally, and those for the le-vator muscle of the upper eyelids (caudal central oculomotor nucleus) (D18) dorso-caudally. In the middle third between the two paired main nuclei there usually lies an unpaired cell group, Perlia’s nucleus, which is thought to be associated with ocular con-vergence.
The preganglionic visceromotor (parasym-pathetic) fibers originate from the parvo-cellular Edinger – Westphal nucleus, the acces-sory oculomotor nucleus (ACD19). They runfrom the oculomotor nucleus to the ciliary ganglion where they synapse. The postgan-glionic fibers enter through the sclera into the eyeball and innervate the ciliary muscle (F20) and the sphincter pupillae muscle(F21).