492 



CAROTID ARTERY. 



arterial circle of the iris. All these arteries, 

 however, do not contribute to form this lesser 

 arterial circle ; a great number pass beyond it, 

 and, along with the branches which arise from 

 its concavity, advance towards the pupil. There 

 are thus three arterial circles in the iris, two 

 close together at its greater circumference or 

 ciliary margin; the third much smaller, sur- 

 rounding its pupillary margin, and commu- 

 nicating with the preceding by a radiation of 

 branches situated on the anterior surface of the 

 iris. 



The anterior ciliary arteries are two 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 

 retinae and one or more ciliary; it passes in- 

 wards to supply the inferior and internal recti 

 muscles, and sends some branches into the 

 nasal fossae. 



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 palpebrse superioris, the 

 periosteum, and the sclerotic. 



6. The posterior ethmoidal 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 fossae 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- 

 cilii, 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 nose ; 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 internal 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; shortly 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. 



After having given off the communicating 

 artery, the carotid sends a branch to the choroid 

 plexus, the arteria choroidea ; the artery passes 



