772 



THE NEKVOUS SYSTEM. 



The large sensory root gradually conceals the small motor root in its course 

 forwards, and expands beneath the dura mater into a large flattened ganglion 

 the semilunar ganglion. This ganglion occupies an impression on the apex of the 

 petrous portion of the temporal bone, and from it three large trunks arise the 

 ophthalmic or first, the maxillary or second, and the mandibular or third divisions 

 of the nerve. The small motor root of the nerve passes forward beneath the 

 ganglion, and is incorporated wholly with the mandibular division of the nerve. 



NERVUS OPHTHALMICUS. 



The ophthalmic nerve passes forwards to the 

 of the skull, in the dura mater. It lies in the 



orbit through the middle fossa 

 lateral wall of the cavernous 

 sinus, at a lower level than the 

 trochlear nerve, and reaches 

 the orbit through the superior 

 orbital fissure (Fig. 645). 



In the wall of the cavernous 

 sinus the ophthalmic nerve gives 

 off (1) a small recurrent branch 

 to the dura mater (n. tentorii], 

 (2) communicating branches to 

 the cavernous plexus of the sym- 

 pathetic on the internal carotid 

 artery, and (3) small communi- 

 cating twigs to the trunks of 

 the oculo-motor, trochlear, and 

 abducent nerves. 



In the, superior orbital 

 fissure the nerve divides into 

 three main branches lacrimal, 

 frontal, and naso-ciliary (Fig. 

 645). 



N. Lacrimalis. -- The 

 lacrimal nerve enters the orbit 

 through the lateral angle 

 the superior orbital fissui 

 above the orbital muscles. 

 It passes forwards, between 

 the periosteum and the orbital 

 contents, to the anterior part 

 of the orbit, and ends by 

 supplying branches (a) to the 

 lacrimal gland, (ft) to the con- 

 junctiva,and (c) to the skin of the 

 lateral commissure of the eye. 



The lacrimal nerve communicates in the orbit with the zygomatic branch of the maxillary 

 nerve, and on the face, by its terminal branches, with the temporal brandies of the facial 

 nerve (Fig. 653). 



N. Prontalis. The frontal nerve enters the orbital cavity through 

 superior orbital fissure, courses forwards above the ocular muscles, and divi( 

 at a variable point into two branches a larger supra-orbital and a smaller supra- 

 trochlear nerve. 



N. Supraorbitalis. The supra - orbital nerve passes directly forwards, anc 

 leaves the orbit through the supra-orbital groove or foramen to reach the forehead 

 It gives off the following secondary branches : (1) the principal (frontal) branche! 

 (rami frontales) are distributed to the forehead and scalp, reaching backwards as 

 far as the vertex ; (2) small branches supply the upper eyelid ; and (3) twigs ar< 



FIG. 648. DISTRIBUTION OF SENSORY NERVES TO 

 THE HEAD AND NECK. 



