726 THE NERVOUS SYSTEM. 



root passes beneath the ganglion without having any connection with it, and joins 

 outside the ci'anium with one of the trunks derived from it. 



The Grasserian or semilunar ganglion l is lodged in an osteo-fibrous space, the 

 cavum Meckelii, near the apex of the petrous portion of the temporal bone. It is 

 of somewhat crescentic form, with its convexity turned forward. Its upper surface 

 is intimately adherent to the dura mater. Besides the small or motor root, the 

 large superficial petrosal nerve lies underneath the ganglion. 



Branches of Communication. This ganglion receives, on its inner side, fila- 

 ments from the carotid plexus of the sympathetic. Branches of Distribution. It 

 gives off minute branches to the tentorium cerebelli and the dura mater in the 



o 



middle fossa of the cranium. From its anterior border, which is directed forward 

 and outward, three large branches proceed the ophthalmic, superior maxillary, 

 and inferior maxillary. The ophthalmic and superior maxillary consist exclu- 

 sively of fibres derived from the larger root and ganglion, and are solely nerves 

 of common sensation. The third division, or inferior maxillary, is joined outside 

 the cranium by the motor root. This, therefore, strictly speaking, is the only 

 portion of the fifth nerve which can be said to resemble a spinal nerve, 



Ophthalmic Nerve (Figs. 391, 393, 394). 



The Ophthalmic (n. ophthalmic us), or first division of the fifth, is a sensory 

 nerve. It supplies the eyeball, the lachrymal gland, the mucous lining of the eye 

 and nasal fossse, and the integument of the eyebrow, forehead, and nose. It is 

 the smallest of the three divisions of the fifth, arising from the upper part of the 

 Gasserian ganglioii. It is a short, flattened band, about an inch in length, which 

 passes forward along the outer wall of the cavernous sinus, below the other nerves, 

 and just before entering the orbit, through the sphenoidal fissure, divides into 

 three branches lachrymal, frontal, and nasal. 



Branches of Communication. The ophthalmic nerve is joined by filaments 

 from the cavernous plexus of the sympathetic, communicates with the third and 

 sixth nerves, and is not infrequently joined with the fourth. 



Branches of Distribution. It gives off recurrent filaments which pass between 

 the layers of the tentorium, and then divides into 



Lachrymal. Frontal. Nasal. 



The lachrymal is the smallest of the three branches of the ophthalmic. It 

 sometimes receives a filament from the fourth nerve, but this is possibly derived 

 from the branch of communication which passes from the ophthalmic to the fourth. 

 It passes forward in a separate tube of dura mater, and enters the orbit through 

 the narrowest part of the sphenoidal fissure. In the orbit it runs along the upper 

 border of the External rectus muscle, with the lachrymal artery, and communi- 

 cates with the temporo-malar branch of the superior maxillary. It enters the 

 lachrymal gland and gives off several filaments, which supply the gland and the 

 conjunctiva. Finally, it pierces the superior palpebral ligament, and terminates 

 in the integument of the upper eyelid, joining with filaments of the facial nerve. 

 The lachrymal nerve is occasionally absent, when its place is taken by the temporal 

 branch of the superior maxillary. Sometimes the latter branch is absent, and a 

 continuation of the lachrvj^r. 1 ,/-^ - v ' 



' " ' tV"> ' st^S* yarded, both 



FIG. 392. riaii of the motor oculi nerve. (After Flower.) 



behind the corpora quadrigemina to the valve of Vieussens, on the upper surface 

 of which the two nerves decussate. Its deep origin may be traced to a nucleus 

 in the floor of the aqueduct of Sylvius immediately below that of the third nerve, 

 Avith which it is continuous. 



