244 



HEAD AND NECK 



to the anterior margin of the orbit, and then, from before 

 backwards, along the middle line of the orbit. Turn the 

 two flaps so marked out laterally and medially respectively. 

 As the region of the superior orbital fissure is approached be 

 careful not to injure the nerves which pass through the fissure ; 

 the one most likely to be injured is the small trochlear nerve 

 which lies near the medial end of the fissure. Secure it at once, 

 and trace it forwards through the fat to the superior oblique 

 muscle which lies along the upper part of the medial walljyTthe 



Lacrimal gland 



Frontal nerve 

 Short ciliary nerves ^- 



Lacrimal nerve 



Ophthalmic nerve 



Infra-trochlear nerve 



-Supra-trochlear nerve 

 Supra-orbital nerve 



- Anterior ethmoidal nerve 

 Long ciliary nerves 



Naso-ciliary nerve 

 Ciliary ganglion 



Optic nerve 



Maxillary nerve 

 Motor root of trigemina 

 'Mandibular nerve 



x Semilunar ganglion (thrown laterally) 



FlG. 91. The Ophthalmic Nerve of the Left Side. The semilunar ganglion 

 and the nerves have been everted and turned over to show the motor root. 



orbit. In the middle line of the orbit the large frontal nerve 

 wiir be found lying in the fat on the surface of the levator pal- 

 pebrae superioris. Trace the nerve forwards to its division into 

 , its two terminal branches : a large supra-orbital branch accom- 

 panied by a corresponding artery, and a medial and smaller 

 supra-trochlear branch. Follow the supra-trochlear branch to 

 the superior medial angle of the orbit, where it passes above 

 the pulley of the superior oblique muscle. Return to the 

 trochlear nerve and the superior oblique muscle ; clean the 

 muscle from behind forwards. It ends in a tendon which passes 

 through the fibrous pulley, situated at the upper and medial 

 angle of the orbit, then turns backwards and laterally, and dis- 



