340 HEAD AND NECK 



above the optic nerve, and that it is closely accompanied by 

 the delicate ciliary nerves and vessels. The optic nerve is 

 slightly longer than the distance which it has to run from the 

 optic foramen to the globe of the eye, so that the movements 

 of the eyeball may not be interfered with. Within the eye- 

 ball the optic nerve spreads out in the retina. 



Nervus Naso-ciliaris. The naso-ciliary nerve (O.T. nasal) 

 arises from the ophthalmic division of the trigeminal in the 

 anterior part of the cavernous sinus. It passes through the 

 superior orbital fissure and enters the orbital cavity, between 

 the two heads of the lateral rectus muscle and between the 

 two divisions of the third nerve. It then inclines antero- 

 medially, and, crossing the optic nerve obliquely, it runs 

 between the medial rectus and superior oblique muscles to 

 the medial wall of the orbit, where it divides into two ter- 

 minal branches viz., the infra-trochlear and the anterior 

 ethmoidal nerves. In addition to these it gives off in the 

 orbit the following branches: (i) long root to the ciliary 

 ganglion; (2) long ciliary nerves; (3) posterior ethmoidal 

 nerve. 



Radix Longa Ganglii Ciliaris. This is a very slender 

 filament which springs from the naso-ciliary as it enters the 

 orbit between the heads of the lateral rectus. It runs along 

 the lateral side of the optic nerve, and enters the upper and 

 posterior part of the ciliary ganglion. 



Nervi Ciliares Longl. The two long ciliary branches 

 spring from the naso-ciliary as it crosses the optic nerve. 

 They pass anteriorly, upon the medial side of the optic 

 nerve, to reach the globe of the eye where they pierce the 

 sclera. One of the long ciliary nerves very constantly 

 unites with one of the short ciliary filaments. 



Nervus Ethmoidalis Posterior passes through the posterior 

 ethmoidal foramen to the ethmoidal cells and the sphenoidal 

 air sinus. 



Nervus Infratrochlearis. The infra-trochlear branch runs 

 along the medial wall of the orbit below the superior oblique 

 muscle. After passing under the trochlea of that muscle it 

 emerges from the orbit and appears upon the face, where it 

 has been dissected already (p. 128). Near the pulley it 

 receives a communicating twig from the supra-trochlear nerve. 

 Nervus Ethmoidalis Anterior. This is the larger of the 

 two terminal branches of the naso-ciliary nerve. It leaves 



