1156 A MANUAL OF ANATOMY 



lying under cover of the dura mater. Having reached the nasal 

 slit at the side of the fore part of the crista galli, it descends 

 through this slit into the nasal fossa, and immediately gives ofi a 

 septal branch. Thereafter the nerve descends in a groove on the 

 posterior surface of the nasal bone, furnishing offsets to the 

 mucous membrane of the outer wall of the nasal fossa, in front of 

 the superior and middle conchae. Finally, the nerve emerges 

 between the lower border of the nasal bone and the upper lateral 

 nasal cartilage, and descends beneath the compressor naris muscle 

 to supply the skin of the tip and lower part of the side of the nose. 



In connection with this remarkable course of the nerve it is to 

 be noted that it is to be met with in four different regions, namely, 

 (i) in the orbit ; (2) on the cribriform plate of the ethmoid bone in the 

 anterior cranial fossa ; (3) in the nasal fossa ; and (4) on the face, 

 in the region of the tip of the nose. 



Branches. — The ganglionic branch forms the long or sensory 

 root of the lenticular ganglion. It is slender, about | inch 

 long, and arises from the nasal as it passes between the two heads 

 of the external rectus. It enters the ciliary ganglion at its postero- 

 superior angle. 



The long ciliary nerves, usually two in number, arise from the 

 nasal immediately after it has crossed the optic nerve, and they 

 communicate with the short ciliary nerves from the ciliary ganglion, 

 which they accompany to the back part of the sclerotic. Here 

 they pierce the sclerotic, and are distributed along with the short 

 ciliary nerves. 



The infratrochlear nerve arises from the nasal close to the anterior 

 ethmoidal foramen, and passes forwards beneath the superior 

 oblique muscle. Near the pulley of that muscle it receives a twig 

 from the supratrochlear nerve, and then, passing beneath the 

 pulley, it emerges from the orbit at the inner canthus to be dis- 

 tributed to the skin and conjunctiva of the inner parts of the eye- 

 lids, the side of the root of the nose, the lachrymal sac, and the 

 caruncula lacrimalis. 



As the nerve traverses the anterior ethmoidal canal it furnishes 

 twigs to the mucous membrane of the frontal air-sinus and of the 

 anterior ethmoidal cells. 



A spheno- ethmoidal or posterior ethmoidal branch is described as 

 passing through the posterior ethmoidal canal to supply the mucous 

 membrane of the posterior ethmoidal cells and of the sphenoidal 

 air-sinus. 



For the branches of the nasal nerve to the exterior of the nose 

 and to the nasal fossa, see p. 1176 and Index. 



Ciliary, Lenticular, or Ophthalmic Ganglion. — ^This is a small 

 quadrilateral body, about the size of a moderately large pin-head, 

 which is situated in the posterior part of the orbit, where it lies 

 flattened upon the outer side of the optic nerve. It is usually in 

 close contact with that nerve, and is recognised by its reddish-pink 

 colour. Posteriorly it receives its three roots, and anteriorly the 



