The anterior ciliary arteries are tl,vo or three in number; sometimes coming from the palpe bral or from the branches which go to the recti muscles; they pass forward to the anterior part of the globe of the eye, where they each di vide into many branches, the smaller of which are distributed to the conjunctiva and the scle rotica, the others pierce the sclerotica, near the circumference of the cornea, pass through the ciliary ligament, and join the arterial circles of the greater circumference of the iris; some passing beyond that circle go to the iris, and others are distributed to the anterior part of the choroid.
5. The muscular arteries generally consist of two, an inferior and a superior. The inferior muscular artery is a branch which is generally present; it sometimes gives off the centralis retinw and one or more ciliary; it passes in wards to supply the inferior and internal recti muscles, and sends some branches into the nasal fossm.
The superior muscular is less regular than the former ; it passes forwards im mediately under the superior wall of the orbit, and di vides into many branches, which are distributed to the superior and internal recti, the superior oblique, the levator palpebrw superioris, the periosteum, and the sclerotic.
6. The posterior ethnioidal artery sometimes arises from the lachrymal or supra-orbital ; it passes inwards between the superior oblique and rectus internus, and enters the foramen orbitarium internum posterius, giving branches to the anterior ethmoidal cells and their lining membrane ; it then enters the cranium, where it is distributed to the dura mater, over the cribriform plate, through the holes of which it sends some branches to the pituitary mem brane, and anastomoses with the anterior ethmoidal.
The anterior ethmoidal artery is given off by the ophthalmic towards the anterior part of the orbit ; it passes through the foramen orbi tarium internum anterius with the nasal branch of the ophthalmic nerve, and after giving branches to the interior of the frontal sinus and anterior ethmoidal cells, it enters the cranium and divides into many branches, some of which go to the dura mater, and others descend into the nasal fossm by the holes in the cribriform plate of the ethmoid bone, and are distributed to the pituitary membrane.
7. The palpebral arteries sometimes arise by a common trunk and sometimes separately.
The superior palpebral arises a little further forward than the inferior; they are distributed to the conjunctiva and to the eyelids, in which they spread out their branches between the skin and the orbicularis muscle. They princi pally divide each into two branches, one of which runs along the tarsal margin, supplying the tarsal cartilage, Meibomian glands, and con junctiva, and the other nearer to the base of the eyelids in an oblique course from within outwards.
The superior palpebral anastomoses with the lachrymal, superciliary, frontal, and an terior branch of the temporal.
The inferior palpebral anastomoses with the infra-orbital, the lachrymal, and nasal.
After the ophthalmic artery has given off the palpebral, it divides into two branches, one of which is the frontal and the other the nasal.
8. The frontal artery is usually the smaller of the two ; it passes out of the orbit at the superior and internal part of the base of that cavity, and divides almost immediately into two or three branches, which ascend on the forehead, over which they ramify, and are dis tributed to the orbicularis, corrugator super pyramidalis nasi, and occipito-frontalis muscles, to the periosteum and common inte guments : these anastomose with the opposite artery, the superciliary, and the temporal.
9. The nasal artery varies in size, being sometimes only a very trifling branch, which terminates at the root of the rime; sometimes its size is considerable, as, when it descends very low, contributing with the lateral nasal branch of the facial to supply the place of the dorsal artery of the nose, in which case it ex tends to the lower part of that organ; it always anastomoses with the facial and inferior pal pebral, and gives branches to the integuments, cartilages, and bones of the nose, to the la chrymal sac, to the corrugator supercilii, and the internal part of the orbicularis palpebrarum.
The ihternal carotid, after it has furnished the ophthalmic artery, is distributed entirely to the brain, especially to its anterior part, the posterior part of that organ receiving its prin cipal supply of blood from the vertebral. Having pierced the dura mater at the external side of the anterior clinoid process, and ex ternal to the optic nerve, the internal carotid artery gives several minute branches to this nerve, to the pituitary gland, the infundibulum, and anterior part of the brain ; slortly after this it gives a branch which is very variable in size, frequently differing in this respect on opposite sides in the same subject; this is the lateral or posterior communicating branch of Willis, which passes backwards and a little inwards, external to the commissure of the optic nerves, infundibulum, tuber cinereum, and the corpora mammillaria, and joins the posterior artery of the cerebrum, which is a branch of the basilar : the motor oculi lies ex ternal to it. In its course it gives small branches to the corpora mammillaria, the crus cerebri, the optic nerves, and the choroid plexus.