THE NERVOUS SYSTEM. 31 1 



2. OPTIC NERVE, special nerve of sight; superficial origin, 

 optic chiasma or commissure formed by union of the optic tracts. 

 The commissure and tracts contain intercerebral fibres, the cere- 

 bro-retinal fibres of the same side, and the cerebro-retinal fibres of 

 opposite sides. Deep origin, the optic tracts arise from optic 

 thalamus, the upper corpora quadrigemina, and corpora genicu- 

 lati; course, diverge and pass forward; exit, optic foramen; 

 distribution, to ganglion cells in the retina. 



3. MOTOR OCULI, motor nerve; superficial origin, inner sur- 

 face of crus cerebri; deep origin, from the oculo-motor nucleus 

 in floor of aqueduct of Sylvius ; course, from inner side of crus 

 cerebri passes forward, descends along external wall of cavernous 

 sinus ; exit, sphenoidal fissure between two heads of external rec- 

 tus muscle; distribution, by superior and inferior divisions, to 

 all the ocular muscles (including the iris) except the external 

 rectus and superior oblique. 



4. TROCHLEAR (pathetic), motor nerve; superficial origin, 

 from valve of Vieussens, on outer side of crus cerebri; deep 

 origin, from floor of aqueduct of Sylvius; course, outer side of 

 crus cerebri, through outer wall of cavernous sinus; exit, sphe- 

 noidal fissure; distribution, to superior oblique muscle. 



5. TRIFACIAL, or TRIGEMINUS, common sensation, taste and 

 motion ; superficial origin, by two roots, like a spinal nerve, from 

 the side of the pons Varolii; deep origin, the motor root, from 

 (1) a nucleus in the floor of the aqueduct of Sylvius (descending 

 motor root), and (2) from a nucleus in the pons (these join to 

 form 'the motor root) ; the sensory root ends in two terminal 

 nuclei (1) the sensory nucleus of the fifth nerve in the pons 

 and (2) the substantia gelatinosa Rolandi in the pons, medulla, 

 and the spinal cord as far down as the second cervical nerve; 

 course, passes forward to apex of petrous portion of temporal 

 bone, where the sensory root enters Gasserian ganglion, the 

 motor passing beneath, and later joins a branch of the ganglion. 

 It divides into three branches ophthalmic, superior maxillary, 

 and inferior maxillary; exit, ophthalmic by sphenoidal fissure, 

 superior maxillary by foramen rotundum, inferior maxillary by 

 foramen ovale. 



Ophthalmic nerve, entirely sensory, supplies lachrymal 

 gland, upper eyelid, skin and muscles of forehead, eyebrow, nose, 

 eyeball (ciliary muscle, iris, etc.), mucous membrane of eyelids 

 and nose, and the ciliary ganglion. 



Its branches are: 



Lachrymal, Frontal, Nasal. 



