THE NERVES OF THE MUSCLES OF THE EYE. 353 



The branch to this latter muscle sends a twig to the 

 ophthalmic ganglion. 



The fourth pair (nervi pathetici or trochleares , Fig. 16,) 

 proceed above the superior rectus and levator palpebrae, 

 obliquely inward and forward, and go to supply the supe- 

 rior ojblique muscle. 



The sixth pair, (motores externi or abducentes,) after pass- 

 ing between the two heads of the rectus externus, proceed 

 outward and forward, and are distributed solely on the 

 ocular surface of this same muscle. 



The fifth pair, (nervi trigemini,) the ophthalmic division^ 

 (Fig. T4,) is the smallest. It proceeds from the superior 

 angle of the Gasserian ganglion, about an inch in length, 

 runs through the cavernous sinus, and here passes above 

 the sixth and below the third and fourth nerves, receiving 

 in this sinus some filaments from the sympathetic. It has 

 a sheath of dura-mater, and on reaching the orbit divides 

 into three branches, 1. The lachrymal; 2. The frontal; 3. 

 The nasal. 



The lachrymal proceeds outward and forward above the 

 rectus externus to the lachrymal gland, and is the small- 

 est of the three branches. It accompanies the lachrymal 

 artery, and as it approaches the gland it divides into two 

 filaments, one of which passes through the malar bone and 

 connects with the facial nerve; the other passes through 

 the spheno-maxillary fissure and connects with the supe- 

 rior maxillary nerve. Its terminating branches are spent 

 upon the lachrymal gland, tunica conjunctiva and upper 

 eyelid. 



The frontal branch is the largest of the three, and pro- 

 ceeds forward above the muscles of the orbit, between them 

 and the periosteum, and on approaching the superior orbi- 

 tary margin divides into an internal and external branch. 

 The internal or supra-trochlear nerve passes above the troch- 

 lea of the superior oblique muscle, connects with the nasal 

 nerve, and is distributed, after passing over the inner mar- 

 gin of the orbit, to the corrugator supercilii ; occipito-fron- 

 talis and orbicularis palpebrarum muscles. 

 23 



