OPHTHALMIC NERVE. 439 



the fibres of the anterior column, the other with the posterior column. 

 Proceeding from this origin the two roots of the nerve pass forward, 

 and issue from the brain upon the anterior part of the crus cerebelli, 

 where they are separated by a slight interval. The anterior is much 

 smaller than the posterior, and the two together constitute the fifth 

 nerve, which in this situation consists of seventy to a hundred fila- 

 ments held together by pia mater. The nerve then passes through 

 an oval opening in the border of the tentorium, near the extremity 

 of the petrous bone, and spreads out into a large serailunar ganglion, 

 the Casserian. If the ganglion be turned over, it will be seen that 

 the anterior root lies against its under surface without having any 

 connection with it, and may be followed onwards to the inferior 

 maxillary nerve. The Casserian ganglion divides into three branches, 

 the ophthalmic, superior maxillary, and inferior maxillary. 



The OPHTHALMIC NERVE is a short trunk, being not more than 

 three quarters of an inch in length ; it arises from the upper angle of 

 the Casserian ganglion, beneath the dura mater, and passes forwards 

 through the outer wall of the cavernous sinus, lying externally to the 

 other nerves ; it divides into three branches. Previously to its divi- 

 sion it receives several filaments from the carotid plexus, and gives off 

 a small recurrent nerve, that passes backwards wilh the recurrent 

 branch, of the fourth nerve between the two layers of the tentorium to 

 the lining membrane of the lateral sinus. 



The Branches of the ophthalmic nerve are, the 



Frontal, 



Lachrymal, 



Nasal. 



The Frontal nerve mounts above the levator palpebrae, and runs 

 forward, resting upon that muscle, to the supra-orbital foramen, through 

 which it escapes -upon the forehead, with the supra-orbital artery. It 

 supplies the conjunctiva and upper eyelid and the integument of the 

 cranium as far as the vertex. 



The frontal nerve gives off but one small branch, the supra-troch- 

 lear, which passes inwards above the pulley of the superior oblique 

 muscle, and ascends along the middle line of the forehead, distributing 

 filaments to the integument, to the inner angle of the eye and root of 

 the nose, and to the conjunctiva. 



The Lachrymal nerve, the smallest of the three branches of the 

 ophthalmic, receives a filament from the fourth nerve in the cavernous 

 sinus, and passes outwards along the upper border of the external 

 rectus muscle, and in company with the lachrymal artery, to the 

 lachrymal gland, where it divides into two branches. The superior 

 branch passes along the upper surface of the gland and through a 

 foramen in the malar bone, and is distributed upon the temple and 

 cheek, communicating with the subcutaneus malae and facial nerves. 



