THE ORBIT 251 



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 eyeball 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 runs forwards and 

 medially, and, crossing obliquely above the optic nerve, 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 those, 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. The long root of the 

 ciliary ganglion 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 Longi. The two long ciliary branches 

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

 They pass forwards, 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. The posterior ethmoidal 

 nerve 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 above 

 the medial commissure of the eyelids, where it has been 

 dissected already (p. 27). Near the pulley it receives a 

 communicating twig from the supra-trochlear nerve. 



Nervus Ethmoidalis Anterior. The anterior ethmoidal 

 nerve is the larger of the two terminal branches of the naso- 



