The ophthalmic artery passes through the optic hole in company with the optic nerve, and inclosed in a sheath derived from the dura mater. It is very tortuous and twines round the optic merve, being at first inferior to the nerve, then passing to its outer side, and soon crossing over it to reach its inner side ; it then passes across to the inner wall of the orbit, where it breaks up into its terminal branches. The branches of the ophthalmic artery are very numerous ; they may be arranged in three sets ; the first set arises from the artery as it lies ex ternal to the optic nerve; it consists of the lachrymal and the centralis retinze ; the second set comes off from the artery, when it is above the optic nerve ; this consists of the supra 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 frontal 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 eriters the orbit through the sphe noidal foramen. It passes forwards along the outer wall of the orbit 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 conju»ctiva and the upper eyelid. It gives a malar branch which passes through the malar bone and anastomoses in the substance of the temporal muscle vvith 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 yl 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 bmnch passes through the vitreous humour and reaches the posterior surface of the capsule of the lens.
l'he supra-orbital artery arises from the oph thalmic while it is above the optic nerve ; it is oEe of the largest branches of the artery : it passes forwards close under the periosteum of the roof, and abOve the levator palpebrx, 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 oecipito-frontalis and the periOsteum. In the orbit it supplies the levator pal pebrm 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 irreg,ular; most of them arise from the ophthalmic arteiy, but oc casionally some from the supra-orbital or from some inuscular 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 levator palpebrx, the superior oblique and the superior rectos 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 rectos and then supplies the inferior and internal 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 ethmoidal 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 mold 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 brafich.