OPHTHALMIC ARTERY. 375 



BRANCHES OF THE INTERNAL CAROTID ARTERY 



In the neck the internal carotid artery gives usually no branch. 

 "While within the carotid canal it sends a small offset to the tympanum, 

 which anastomoses with the tympanic and stylo-mastoid arteries. 

 Within the cavernous sinus some small branches proceed from it to 

 supply the walls of the sinus and the adjacent dura mater. 



Opposite the anterior clinoid process, the internal carotid gives off the 

 ophthahnic artery ; and at the Sylvian fissure of the brain, before 

 dividing into the antBrior and middle cerebral arteries, it gives off or is 

 joined by the poBterior communicaiing artery, a slender anastomotic 

 branch which unites the internal carotid with the posterior cerebral 

 branch of the basilar artery. 



1. Ophthalmic Artery. — This artery, arising from the internal 

 carotid artery by the side of the anterior clinoid process, enters the 

 orbit by the foramen opticum, below and to the outer side of the optic 

 nerve. It soon changes its direction, passing over the nerve to reach 

 the inner wall of the orbit, along which it runs forwards, and terminates 

 in branches which ramify on the forehead and side of the nose. 



Branches. — (</) The laclnm^^iid' artery, arising on the outer side of the optic 

 nerve, passes forwards along the upper border of the external rectus muscle to 

 the lachrymal gland, in which the greater number of its branches are distributed. 

 Some of the branches pass onwards to the eyelids and conjunctiva, joining vritYi 

 other palpebral branches ; and one or two delicate inula r branches pierce the 

 malar bone and reach the temporal fossa, where they join branches from the deep 

 temporal arteries. The lachrjTiial artery has also branches of communication 

 through the sphenoidal fissure with small offsets from the middle meningeal 

 artery. 



(A) The central artery of the 7-ctina, a very small vessel, pierces the sheath and 

 substance of the optic nerve about a quarter of an inch behind its junction with 

 the eyeball, and runs imbedded within it to the retina, in which it ramifies in 

 minute branches. In the foetus, a very delicate vessel passes forwards through 

 the vitreous humour, to reach the posterior surface of the capsule of the crystal- 

 line lens. 



{(■) The siipraorhital branch ascends above the muscles, and coursing forwards 

 to the supraorbital notch, in company with the frontal nerve, terminates on the 

 forehead. It distributes branches to the eyelids, and communicates with the 

 temporal artery. 



{(l) Tlie cUiarij arteries are divisible into three sets, viz., short, long, and 

 anterior ciliary. The short ciliary arteries, varying from twelve to fifteen in 

 number, enclose the optic nerve as they pass forwards to reach the posterior 

 aspect of the sclerotic coat, which they pierce, and enter the eyeball about a line 

 or two from the entrance of the optic nerve. The loiuj ciliary arteries, two in 

 number, also enter the back of the eyeball, and then pass forwards, one on each 

 side, between the choroid and sclerotic coats, as far as the ciliary ligament, where 

 they divide into branches. The anterior ciliary arteries are derived from some of 

 the muscular branches ; they form a vascular circle around the fore part of the 

 eyeball, and then pierce the sclerotic within a line or two of the margin of the 

 cornea. All these ciliary arteries anastomose together within the eyeball, their 

 distribution in which will be particularly described with the anatomy of the 

 eyeball. 



(-") The mmcular branches, subject to much variety, usually arranged in an 

 upper and lower set, supply the muscles of the orbit. 



(/) The ethmoidal branches are two in number, a j?osterior and an anterior. 

 They pass through the posterior and anterior internal orbital foramina, the 

 latter in company with the nasal branch of the ophthalmic nerve ; and both 



