360 INTERNAL CAROTID ARTERY. 



The vertebral artery is similarly tortuous before entering the cranium. 



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

 branch. While within the carotid canal it sends a small offset to the tym- 

 panum, 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 

 ophthalmic artery ; and at the Sylvian fissure of the brain, before dividing 

 into the anterior and middle cerebral arteries, it gives off or is joined by the 

 posterior communicating artery, a slender anastomotic branch which lies 

 parallel to its fellow of the opposite side and unites the internal carotid 

 with the posterior cerebral artery. 



PECULIARITIES. In very rare cases of abnormal arrangement of the arch of the 

 aorta, the internal carotid artery has arisen as a primary trunk. A few examples of 

 its entire absence are recorded. 



The posterior communicating artery has been occasionally seen replaced by two 

 very small vessels. 



BRANCHES OF THE INTERNAL CAROTID ARTERY. 



1. OPHTHALMIC ARTERY. 



The ophthalmic 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 : 



(a) The lachrymal 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 with other palpebral 

 branches ; and one or two delicate malar branches pierce the malar bone and reach 

 the temporal fossa, where they join branches from the deep temporal arteries. The 

 lachrymal artery has also branches of communication through the sphenoidal fissure 

 with small offsets from the middle meningeal artery. 



(6) The central artery of the retina, 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. A very delicate vessel, demonstrable in the feetus, passes forwards through 

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

 line lens. 



(c) The supraorbital 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. 



(d) The ciliary 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 long ciliary arteries, two in number, also enter the back of 

 the eyeball, and then pass forwards, one on each side, between the choroid mem- 

 brane and the sclerotic, 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 



