THE THIRD NERVE OR MOTOR OCULI 



549 



Nerves of motion. 



Mixed nerves. 



\ The Motor Oculi; Trochlearis, lesser division of 

 ( the Trigeminal, Abducens, Facial, and Hypoglossal. 



j Facial, Glosso-pharyngeal, Vagus, and Spinal Ac- 

 ( cessory. 



The physiology of the first, second, and eighth nerves will be considered 

 with the Organs of Special Sense. 



The Third Nerve or Motor Oculi. Origin. The third nerve arises 

 in three distinct bands of fibers from the gray nuclei surrounding the aqueduct 

 of Sylvius near the middle line, but ventral to the canal. The nucleus of origin 

 consists of large multipolar ganglion cells, and extends to the back part of the 

 third ventricle as far as the level of the superior corpora quadrigemina. The 



FIG. 383. Section through Anterior Corpus Quadrigeminum and Part of Optic Thalamus. s, 

 Aqueduct of Sylvius, gr, gray matter of the aqueduct , c.q.s, quadrigeminal eminence; /, stratum 

 lemnisci; o, stratum opticum, c, stratum cinereum ; Th, pulvinar of optic thalamus: c.g.e, c.g.i, 

 lateral and median corpora geniculata; br.s, br.t, superior and inferior brachia, f, fillet; p.l, 

 posterior longitudinal bundle; r, raphe; ///, third nerve, and n.IIl, its nucleus; l.p.p, posterior 

 perforated space; s.n, substantia nigra above this is the tegmentum with the circular area of the 

 red nucleus; cr, crusta; //, optic tract; M, medullary center of hemisphere; n.c, nucleus cau- 

 datus; st, stria terminalis. (After Quain, from Meynert.) 



fibers pass from their origin partly through the red nucleus to their superficial 

 origin in front of the pons at the median side of each crus. They decussate in 

 the middle raphe. 



Function. The third nerve supplies the levator palpebrae superioris mus- 

 cle, and all of the muscles of the eyeball, except the superior oblique, to 

 which the fourth nerve is appropriated, and the rectus externus, which receives 

 the sixth nerve. Through the medium of the ophthalmic or lenticular ganglion, 

 of which it forms what is called the short root, it also supplies motor filaments 

 to the iris and ciliary muscle. The fibers which subserve the three functions, 

 accommodation, contraction of the pupil, and nerve-supply to the external 

 ocular muscles, arise from three distinct groups of cells. Optic reflexes in- 

 volving movements of the eyeballs are through fibers from cells of the superior 

 corpora quadrigemina (which receive fibers from the optic nerve). These 



