786 



ORBIT. 



orbital, ciliary and muscular; the third is given 

 off when the artery has passed over to the nasal 

 side of the orbit, and consists of the ethmoidal, 

 palpebral, nasal, and fronlal arteries. 



The lachrymal artery is one of the largest 

 branches of the ophthalmic ; it arises from the 

 ophthalmic either within the optic hole or imme- 

 diately after that artery has entered the orbit. 

 It sometimes arises from the middle meningeal 

 artery, and enters the orbit through the sphe- 

 noidal foramen. It passes forwards along the 

 outer wall of the oibit between the periosteum 

 and the external rectus muscle; it enters the 

 lachrymal gland, sending numerous branches to 

 it ; it then emerges from the gland and supplies 

 the conjunctiva and the upper eyelid. It gives 

 a malar branch which passes through the malar 

 bone and anastomoses in the substance of the 

 temporal muscle with the anterior deep tem- 

 poral artery. The lachrymal artery generally 

 anastomoses with the middle meningeal by a 

 branch sent in through the sphenoidal fissure. 



The central artery of the, retina is a small 

 branch which enters obliquely the optic nerve; 

 it passes forwards in the centre of the nerve, 

 enters the globe of the eye, and expands out 

 into a vascular membrane on the inner surface 

 of the retina. One small branch passes through 

 the vitreous humour and reaches the posterior 

 surface of the capsule of the lens. 



The supra-orbital artery arises from the oph- 

 thalmic while it is above the opiic nerve ; it is 

 one of the largest branches of the arteiy : it 

 passes forwards close under the periosteum of 

 the roof, and above the levator palpebrse, in 

 company with the frontal nerve. It escapes 

 from the orbit at the supra-orbital notch, and 

 sends branches on the forehead, some between 

 the skin and muscles, and others between the 

 occi pi to-frontal is and the periosteum. In the 

 orbit it supplies the levator palpebrae and supe- 

 rior rectus muscles, and sends some branches 

 to the upper lid. 



The ciliary arteries are very numerous, and 

 are divided into three sets anterior, middle, 

 and posterior. The anterior ciliary arteries are 

 irregular in number and origin ; they usually 

 come off from the muscular branches at the 

 anterior part of the orbit ; they perforate the 

 sclerotic about one or two lines behind the 

 cornea : some branches go to the iris and anas- 

 tomose with the long ciliary arteries; others go 

 to the choroid and anastomose with the short 

 ciliary. The middle or long ciliary arteries are 

 two in number; they accompany the nerves of 

 the same name. They pierce the sclerotic at 

 some distance from the optic nerve, and pass 

 horizontally one on each side between the scle- 

 rotic and the choroid. They pass through the 

 ciliary ligament and supply the iris. The pos- 

 terior or short ciliary arteries are remarkably 

 delicate and tortuous ; they are accompanied by 

 the ciliary nerves from the lenticular ganglion. 

 Their origin is somewhat irregular; most of 

 them arise from the ophthalmic artery, but oc- 

 casionally some from the supra-orbital or from 

 some muscular branches. There are as many as 

 fifteen or twenty of these arteries, which sur- 

 round the optic nerve in a spiral and tortuous 



manner; they pierce the sclerotic about two 

 lines anterior to the entrance of the optic nerve, 

 and supply the choroid and ciliary processes. 

 (For the mode of arrangement of these ciliary 

 vessels in the choroid and iris see the article 

 EYE.) 



The muscular branches are uncertain in num- 

 ber and origin ; they usually consist of two 

 sets, a superior and an inferior. The superior 

 set often come from the frontal artery, and 

 supply the levalor pa)peb>-ce, the superior 

 oblique and the superior recius muscles. The 

 inferior muscular artery is a regular branch 

 from the ophthalmic ; it descends on the inner 

 side of the optic nerve ; it first sends a branch 

 to the external rectus and then supplies the 

 inferior and infernal recti, and the inferior 

 oblique; some branches pass on to the lower 

 eyelid and the lachrymal sac. These arteries 

 are usually distributed to the ocular surface of 

 the muscles. 



The ellnnoidal arteries, two in number, are 

 given off from the ophthalmic near the inner 

 wall of the orbit. The posterior is usually the 

 larger ; it passes through the posterior orbital 

 foramen and enters the skull, where it sends off 

 some anterior meningeal branches, then passes 

 down through the cribriform plate of the eth- 

 moid bone, and is distributed on the mucous 

 membrane of the nose. The anterior ethmoidal 

 passes through the anterior internal orbital fora- 

 men with the nasal nerve ; it has the same 

 distribution as the posterior branch. 



The pulpe brat arteries, two in number, arise 

 near the inner angle of the orbit. The superior 

 arises above the tendon of the orbicularis palpe- 

 brarum; it passes outwards and supplies the 

 upper lid, one branch running near the tarsal 

 margin of the lid, while the others are distri- 

 buted to the muscles and integuments of the 

 middle and upper part of the lid, where they 

 anastomose with the supra-orbital artery. The 

 inferior palpebral artery passes down behind 

 the tendon of the orbicularis, then runs out- 

 wards along the lower lid, forming an arch 

 near the free margin of the lid, and is gradually 

 lost near the external canthus. It anastomoses 

 with the angular branch of the facial, with the 

 infra-orbital branch of the internal maxillary, 

 with the transverse facial and temporal arteries. 

 Beneath the internal angular process the oph- 

 thalmic arteiy terminates by dividing into the 

 nasal and the frontal branches. 



The nasal artery emerges from the orbit 

 above the tendon of the orbicularis ; it anasto- 

 moses freely with the angular artery, sends 

 branches to the lachrymal sac, and terminates 

 in a branch which passes down the dorsum of 

 the nose, and communicates at the extremity 

 of the nose with the corresponding artery of 

 the opposite side. 



The frontal artery passes out of the orbit 

 with the nasal, then turns upwards, and is dis- 

 tributed to the muscles and integuments of the 

 forehead, anastomosing with the supra-orbital 

 and with the arteries of the opposite side. 



The ophthalmic vein commences at the inner 

 angle of the orbit, where it communicates freely 

 with the angular and frontal veins ; it passes 



