CRANIAL NERVES AT EXIT FROM SKULL. 35 



the cavernous sinus to the sphenoidal fissure ; entering the 

 orbit, it crosses the levator palpebrse at its origin, and 

 supplies the trochlearis or superior oblique muscle. 



The FIFTH, or TRIFACTAL NERVE, the largest of the nine 

 pairs of nerves, consists of two parts or roots. These 

 two portions pass through the tentorium close to the apex 

 of the petrous portion of the temporal bone ; the larger 

 division, immediately on reaching the middle fossa of the 

 skull, expands into a flattened ganglion, the Gasserian ; 

 the smaller division lies beneath the ganglion, and is only 

 seen by turning it over. These two roots are distinct from 

 each other, and the smaller one may be traced onward to 

 the inferior maxillary nerve which it joins outside of the 

 cranium. 



The Gasserian ganglion gives off three branches the 

 ophthalmic, and the superior, and inferior maxillary 

 nerves. 



The ophthalmic nen-e, arising from the upper portion of the ganglion, 

 passes through the onter wall of the cavernous sinns, and enters the 

 orbit through the sphenoidal fissure. It divides into three branches 

 nasal, frontal, and lachrymal. 



* The nasal branch passes between the two heads of the external 

 rectus muscle, crosses the optic nerve, and enters the anterior eth- 

 moidal foramen ; it then reappears in the cranium at the side of the 

 crista galli, and enters the nasal cavity, in front of the cribriform 

 plate, to be distributed to the mucous membrane and integument of 

 the nose.- As the nasal nerve enters the orbit, it sends a branch to 

 the lenticular ganglion. The frontal branch passes forward upon the 

 levator palpebra? muscle to the supra-orbital foramen, where it 

 emerges to supply the integument of the forehead. The lachrymal is 

 the smallest of the three branches. It passes along the upper border 

 of the external rectus muscle to the lachrymal gland and upper eye- 

 lid, to which it is distributed. 



The superior maxillary nerve, the second or middle division of the 

 fifth pair, passes out at the foramen rotundum, crosses the spheno- 

 maxillary fissure, and enters the orbit by the canal in its floor, in 

 company with the infra-orbital artery, one of the terminal branches 

 of the internal maxillary ; they both emerge at the infra-orbital fora- 

 men (p. 10), beneath the levator labii superioris muscle, and, forming 

 a plexus with branches of the facial nerve, supply the lower eyelid, 

 upper lip, nose, and cheek. 



* This nerve gives off an orbitar branch, which, entering the orbit 

 through the spheno-maxillary fissure, divides into two branches; 

 these pass through foramina in the malar bone, and are distributed to 

 the temporal fossa, forehead, and cheek. Dental branches also pene- 

 trate through small foramina in the tuberosity of the superior max- 

 illary bone to the molar teeth, and from the infra-orbital canal 

 through the lining membrane of the antruin to the anterior teeth. 



