THE ORBIT 245 



appears below the levator palpebrae superioris and the superior 

 rectus. Define both the tendon and the pulley. Return to the 

 frontal nerve, pull it aside and clean the levator palpebrae 

 superioris, upon which the nerve lies. Define the margins of 

 the levator palpebras and note that it lies upon the superior 

 rectus muscle of the eyeball. Raise the levator palpebrae, 

 carefully, and note a small twig of the superior division of the 

 ocular motor nerve which pierces the superior rectus and enters 

 the levator palpebrae. Now find the lacrimal nerve and the 

 accompanying lacrimal artery, which lie in the fat at the junction 

 of the roof with the lateral wall of the orbit, and trace them 

 forwards to the lacrimal gland. The gland lies under cover of 

 the lateral end of the superior orbital margin. When all the 

 structures which have been mentioned have been found and 

 cleaned study them in detail. 



Nervus Frontalis. The frontal jie^v^ is thp continuation 

 of the stem of the ophthalmic division of the trigeminal 

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

 Branches. It enters the orbit through the superior orbital 

 fissure, above the muscles, and runs forwards, 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. 47). In the orbit it gives off 

 one small twig close to the pulley of the superior oblique 

 muscle ; the twig 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. 

 47). The division of the supra-orbital nerve into a lateral 

 and a medial branch was seen during the dissection of the 

 scalp (p. 47). Sometimes the separation takes place within 

 the orbit, and in that case the larger lateral part occupies 

 the supra-orbital notch. 



Nervus Lacrimalis. The lacrimal nerve is the smallest 

 of the terminal branches of the ophthalmic division of the 

 trigeminal. It enters the orbit through the superior orbital 

 fissure, above the level of the muscles, and runs forwards, 



in 16 & 



