NERVES OF THE ORBIT 104:$ 



supplies part of the inferior rcctus ami inferior oblique muscles in the cavity, and 

 also gives a branch to the 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, pass through the .-uperior orliital tissure and empty into the 

 cavernous sinus. The inferior vein is connected with the pterygoid plexu.- by a 

 liranch which leaves the orbit by the inlcrior orbital fisMire. 



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

 enter the orbil by I he superior orbital fissure, with the exception of one sm.'tll sciiMiry 

 branch passing through the inferior orbital fissure. (The optic nerve has been 

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



A. The motor nerves are the third, fourth, and'si.xth cranial. 



1. The third nerve enters the orbit in two parts, an upper smaller, and a lower 

 larger, division. The upper dinsion gives off two branches: one supplies the supe- 

 rior rectus, entering its lower surface far back; the other branch goes to the levator 

 palpebr:! 1 , entering its lower surface in its posterior third. The lotnr diiision 

 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 lower division gives (1) 

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



74'J. -SKI i [ov THROUGH CONTEXTS OF RlOHT ORBIT, 1-2 MM. IN FRONT OF THE Ol'TIC 

 KoliVMEV, VIEWED FROM BEHIND. (After LftngC.) 



Ophthalmic vrin 

 OrilTIU LMir M-IIVE 



in.erna, reo.u. n,u. Ol e 



Inferior rcctua muscle 



and the remainder of this branch then enters the lower surface of the inferior oblique 

 muscle about its middle. 



2. The fourth nerve supplies the superior oblique muscle, entering its upper 

 surface about midway in its course. 



3. The sixth nerve supplies the external rectus, entering its inner surface about 

 the junction of the posterior 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 breaks up into numerous bundles, 

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

 ing off fine twins supplying the muscle throughout with nerve-ondings. The poste- 

 rior third of these muscles is, however, comparatively ill supplied with both kinds 

 of plexuses and with nerve-endings. 



H. The sensory nerves are supplied by the first and second divisions of the 

 fifth cranial nerve. The first division, or ophthalmic nerve, is entirely orbital; 

 while the second, or maxillary, only sends a small liranch to the orbit. 



1. The ophthalmic division of the fifth nerve enters the orbit in three divi- 

 sions, namely: 



(1) Frontal, splitting subsequently into supratrorhlrar and tvpraorbital, both 

 passing out of the orbit. It is distributed to the corresponding upprr eyelid, and 

 the skin over the root of the nose, the forehead, and the hairy seal]) as far back as 

 the coronal suture on the same side. It also gives branches to the periosteum in 

 this region, and to the frontal sinus. 



