ORBITAL VESSELS AND NERVES 



1075 



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

 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 this artery supplies part of the inferior 

 rectus and 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 superior orbital fissure and empty into the cavernous sinus. The inferior vein 

 is connected with the pterygoid plexus by a branch which leaves the orbit by the inferior orbital 

 fissure. 



Nerves of the orbit. — These are (A) motor, (B) sensory, and (C) sympathetic, and all 

 enter the orbit by the superior orbital fissure, with the exception of one small sensory 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 oculomotor, trochlear, and abducens. 



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

 larger, division. The upper division [ramus superior] gives off two branches: one supplies the 

 superior rectus, entering its lower surface far back; the other branch goes to the levator pal- 

 pebrae, entering its lower surface in its posterior third. The lower division [ramus inferior] 

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



Fig. 819. — The Blood-vessels of the Left Orbit, viewed from above. 



Supraorbital artery 



Lacrimal gland 



Superior rectus, cut 



Eyeball 



Lateral rectus 

 Lacrimal artery 



Superior rectus, cut 

 Inferior ophthalmic vein 

 Superior ophthalmic vein 



Optic nerve 

 Superior ophthalmic vein 



Commencement of superior 

 ophthalmic vein 



Reflected tendon of superior 

 Ophthalmic artery 



Anterior ethmoidal artery 



Posterior ethmoidal artery 

 Ciliary arteries 



T]l Levator palpebrae, cut 

 Common tendon ring 

 (of Zinn) 



Ophthalmic artery 

 Optic chiasma 



Internal carotid artery 



far back, and another supplies the medial rectus, entering its medial 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, and the remainder of this branch then enters 

 the lower surface of the inferior oblique muscle about its middle. 



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

 about midway in its course. 



3. The abducens nerve supplies the lateral rectus, entering its medial 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 sending off fine twigs supplying the muscle 

 throughout with nerve-endings. The posterior third of these muscles is, however, comparatively 

 poorly supplied with both kinds of plexuses and with nerve-endings. 



B. The sensory nerves are supplied by the ophthalmic and maxillary divisions of the 

 trigeminal cranial nerve. The ophthalmic division is chiefly orbital; while the maxillary 

 sends only a small branch to the orbit. 



1. The ophthalmic division of the trigeminal nerve enters the orbit in three divisions, 

 namely : — 



(1) Frontal, splitting subsequently into supratrochlear and supraorbital, both passing out 

 of the orbit. It is distributed to the corresponding upper eyehd, and the skin over the root of 

 the nose, the forehead, and the hairy scalp 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. 



(2) Lacrimal, supplying the lacrimal gland, anastomosing with a branch of the maxillary 



