336 HEAD AND NECK 



Nervus Frontalis. The frontal nerve is the continuation 

 of the stem of the ophthalmic division of the trigeminnl 

 nerve, after it has given off its lacrimal and naso-ciliary 

 branches. It enters the orbit through the superior orbital 

 fissure, above the muscles, and runs anteriorly upon the upper 

 surface of the levator palpebrae superioris, immediately sub- 

 jacent to the periosteal lining of the orbital cavity. It ends 

 at a variable distance from the orbital opening by dividing 

 into the supra-orbital and supra-trochlear branches. 



The supra-trochlear nerve is the medial and smaller of the 

 two terminal branches of the frontal. It runs towards the 

 trochlea of the superior oblique muscle, above which it pierces 

 the palpebral fascia, leaves the orbit, and turns round the 

 orbital arch to reach the forehead. Its further course has 

 been described already (p. 156). In the orbit it gives off 

 one small twig close to the pulley of the superior oblique 

 muscle. This passes downwards to join the infra-trochlear 

 branch of the naso-ciliary nerve. 



The supra-orbital nerve is continued onwards, in the line 

 of the parent stem, and, passing through the supra-orbital 

 notch or foramen, it turns upwards on the forehead (p. 

 156). In the dissection of the scalp this nerve has been 

 seen to divide into a lateral and a medial division. Some- 

 times the separation takes place within the orbit, and in 

 that case the larger lateral part occupies the supra-orbital 

 notch. 



Nervus Lacrimalis. This is the smallest of the terminal 

 branches of the ophthalmic division of the fifth. It enters 

 the orbit through the superior orbital fissure, above the level 

 of the muscles, and runs anteriorly, along the lateral wall of 

 the cavity, above the upper margin of the lateral rectus 

 muscle. At the anterior part of the orbit it continues its 

 course, under cover of the lacrimal gland, until it reaches 

 the lateral part of the upper eyelid, in which it ends (p. 137). 

 Within the orbital cavity it gives numerous twigs to the deep 

 surface of the lacrimal gland, and sends downwards a filament 

 which connects it with the zygomatic branch of the maxillary 

 nerve. 



Nervus Trochlearis. The small fourth nerve is destined 

 entirely for the supply of the superior oblique muscle. Having 

 entered the orbit through the superior orbital fissure, above the 

 muscles, it passes antero-mcdially, under the periosteum, and 



