THE TRIGEMINAL NERVE 65 



of the cavernous sinus, where it is related to the third, fourth 

 and sixth cerebral nerves, the internal carotid artery, and 

 the hypophysis (pituitary body) (Fig. 31). At the anterior 

 extremity of the sinus, it enters the orbit through the superior 

 orbital (sphenoidal) fissure and breaks up into its terminal 

 branches. 



(a) The Frontal Nerve passes forwards in contact with 

 the roof of the orbit and divides into the supra-orbital and the 

 supra-trochlear nerves. The supra-orbital passes forwards and 

 leaves the orbit through the supra-orbital notch, which may be 

 felt on the upper border of the base of the orbit (orbital aper- 

 ture) at a distance of two fingers'-breadth from the median 

 plane. It then turns upwards and supplies a wide area of the 

 skin of the forehead and scalp, extending as far back as the 

 vertex (Fig. 37). In addition, the supra-orbital nerve supplies 

 the skin and the underlying conjunctiva of rather more than 

 the middle third of the upper eyelid. The sympathetic fibres 

 which supply the ciliary bundle (p. 210) are probably carried 

 by the supra-orbital nerve. 



The supra-trochlear is a much smaller nerve, which supplies 

 the skin and conjunctiva of the medial part of the upper eyelid 

 and gives a few twigs to the skin of the forehead just above the 

 root of the nose (Fig. 37). 



(b) The Lacrimal Nerve passes forwards along the upper 

 border of the lateral rectus muscle and receives a communicat- 

 ing branch from the zygomatic (orbital) nerve, which conveys 

 the secreto-motor fibres (p. 69) for the lacrimal gland. After 

 supplying the gland (p. 208), the nerve is distributed to the 

 skin and conjunctiva of the lateral part of the upper eyelid 



(Fig- 37)- 



(c) The Naso-ciliary (Nasal) Nerve runs forwards across 

 the optic nerve to the medial wall of the orbit. It gives off 

 the long root to the ciliary ganglion and the long ciliary nerves, 

 which pass forwards to the coats of the eyeball. In addition, 

 it supplies the skin in the region of the medial canthus by 

 means of the infra-trochlear nerve. The terminal branch of 



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