NERVES OF ORBIT 



8G3 



remarkable for their tortuous course, for their delicate walls, and for their loose 

 attachment to the surrounding^ tissues. The oplithalmic artery gives off si)ecial 

 branches in the orl)it to the lachrymal gland, tlie muscles, the retina (through the 

 optic nerve), and the eyeball, as well as to the meninges, the ethmoidal cells, and the 

 nasal mucous memln-ane. Twigs from all the different l)ranclies go to sui)iily the 

 fat, fasciffi, and ordinary nerves of the orbit. Branches which leave the orl)it ante- 

 riorly ramify on the forehead and nose, and also go to the supply of the eyelids 

 and the tear-passages. The ophthalmic artery has many anastomoses with Ijranches 

 of the external carotid. The contents of the orbit are also supplied in part by the 

 infraorbital artery, a branch of the internal maxillary; in particular tliis artery 

 sui)plies part of tlie inferior rectus and inferior o1)li(iue muscles in the cavitv, and 

 also gives a branch to tlie lower eyelid. 



Veins. — Branches, corresponding generally to those of the artery, unite to form 

 the superior and inferior ophthalmic veins, which ultimately, either separately 

 or united into one trunk, ])ass through tlie si)lienoidal fissure and empty into tlie 

 cavernous sinus. The inferior vein is connected with the pterygoid jilexus ])y a 

 l)raiich which leaves tlie orbit by the spheno-maxillary fissure. 



Nerves of the orbit. — These are motor, sensory, and sympathetic, and all 

 enter the orbit by the sphenoidal fissure, with the exception of one small sensory 



Fig. 490. — Section' tiikough Contexts of Right Orbit. 1-2 mm. ix froxt of the Optic 

 Foramen, viewed from beuind. (After I.ange.) 



FOURTH XER\ I 



Superior rectus and levator 

 palpebrse superioris uiuscles 



Superior oblique muscle 



OPTIC SER VE 



Internal rectus muscle 



Inferior rectus muscle 





Ophlhalmic rein 



onilTIlALMir XERVE 

 (/ROXT.IL, .v.). v.)/,, 

 AX It J.KHRYMAL 

 RRAXCIIES) 



T Ophthahnic vein 



Ophthalmic artery 

 SIXTH XERVE 



THIRD XERVE 

 External rectus muscle 



branch pa.ssing througli the spheno-maxillary fissure. (The optic nerve has been 

 already described, and is not included in this account. ) 



A. The motor nerves are the third, fourth, and sixth cranial. 



1. The third nerve enters the orbit in two parts, an u})per smaller, and a 

 lower larger division. The upper division gives off two branches: one su]tplies tlie 

 superior rectus, entering its lower surface far back; the other Ijranch goes to the 

 levator palpebne, entering its loAver surface in its posterior third. The loner diri-fitrn 

 divides into three branches, of which one supplies the inferior rectus, entering its 

 upper surface far back, and another supplies the internal rectus, entering its inner 

 surface a little behind its middle. The third branch of the loAver division gives ( 1 ) 

 the short root to the ciliary ganglion, and (2) one or more twigs to the inferior 

 rectus, and the remainder of this branch then enters the lower surface of tlie inferior 

 oblique muscle about its mid<lle. 



2. The fourth nerve sui)))lies the superior oblique muscle, entering its ui)i»er 

 surface about midway in its course. 



3. The sixth nerve su])plies the external rectus, entering its inner surface abdut 

 the junction of the ])osterior and middle thirds of the muscle. 



As regards the manner of termination of these motor nerves, it is found that 

 in all the ocular muscles the nerve on its entrance lireaks up into numerous ]iun<lles 

 of fibres, which form first coarse and then fine plexuses, the latter ultimately 

 sending off fine twigs supplying the muscle throughout with nerve-endings. The 



