CAROTID ARTERY. 



491 



a third turn upwards under the anterior clinoid 

 process, and passing backwards and a little in- 

 wards it perforates the dura mater between the in- 

 ternal side of this process and the commissure of 

 the optic nerves. The only vessels which it gives 

 from its entrance into the foramen caroticum to 

 the place where it perforates the dura mater are 

 one or two small branches which perforate the 

 petrous portion of the temporal bone, and pass 

 to the cavity of the tympanum, and as it lies 

 beside the cavernous sinus, two or three little 

 twigs to the dura mater, pituitary gland, body 

 of the sphenoid bone, and to the third, fourth, 

 fifth, and sixth pairs of nerves which lie ex- 

 ternal to it and in contact with the outer or 

 inner wall of the cavernous sinus. 



The ophthalmic artery arises from the an- 

 terior side of the carotid while that vessel is 

 passing into the dura mater, by the side of the 

 anterior clinoid process ; it enters the foramen 

 opticum at first external and inferior to the 

 optic nerve, over which it mounts obliquely 

 towards its internal side, passing between it and 

 the superior rectus muscle of the eye; it then 

 directs its course along the superior and internal 

 part of the orbit between the obliquus superior 

 and rectus internus, towards the inner canthus 

 of the eye where it terminates. Before entering 

 the orbit it gives off a few small twigs to the 

 dura mater and cavernous sinus, and within 

 the orbit it furnishes the following branches: 

 1. the lachrymal; 2. the arteria centralis 

 retinae; 3. the supra-orbital; 4. the ciliary; 5. 

 the muscular; 6. the ethmoidal; 7. the palpe- 

 bral ; 8. the frontal ; and 9. the nasal. 



The order in which these arteries arise from 

 the ophthalmic presents many varieties; but 

 they are constant in their distribution. 



1. The. lachrymal artery is one of the largest 

 branches of the ophthalmic: it sometimes comes 

 from the middle meningeal, and enters the 

 orbit by the foramen lacerum orbitaleof the sphe- 

 noid bone. It runs forwards between the ex- 

 ternal wall of the orbit and the rectus externus, 

 giving branches to that muscle, the periosteum, 

 levator palpebrae superioris and sheath of the 

 optic nerve. One of its branches traverses the 

 malar bone, and entering the temporal fossa 

 anastomoses with the anterior deep temporal ; 

 another little branch frequently traversing this 

 bone passes outwards through the same hole 

 with the nervus subcutaneus malae, and anas- 

 tomoses with branches of the transversalis faciei. 

 The continuation of the artery then divides into 

 several branches which are distributed to the 

 lachrymal gland and the external part of the 

 upper eyelid, anastomosing with the palpebral 

 and the temporal arteries. 



2. The central artery of the retina (arteria 

 centralis retina) penetrates the substance of 

 the optic nerve to enter a canal in its centre, 

 the porus opticus, in which it passes forwards, 

 and is distributed to the retina, the vascular 

 layer of which it forms by its ramifications. 



3. The supra-orbital arises after the centralis 

 retinae, passes forwards along the superior wall 

 of the orbit above the levator palpebrae supe- 

 rioris and superior rectus, giving branches to 

 these muscles, the periosteum, and the scle- 



rotic : on reaching the margin of the orbit, it 

 passes out through the superciliary foramen, 

 along with the frontal branch of the ophthalmic 

 nerve, giving in its passage a branch which 

 enters the substance of the frontal bone ; this 

 artery then mounts beneath the corrugator su- 

 percilii and orbicularis palpebrarurn muscles, 

 and is expended on these muscles, the occipito- 

 frontalis and the integuments ; it anastomoses 

 with branches of the lachrymal and frontal. 



4. The ciliary arteries sometimes amount in 

 number to thirty or forty; they consist of three 

 sets : the posterior or short, the long, and the 

 anterior. The posterior ciliary arteries are very 

 numerous, sometimes amounting in number to 

 thirty or forty: although mostly arising from 

 the ophthalmic, some of them come from the 

 inferior muscular, the supra-orbital, posterior 

 ethmoidal or lachrymal; they run along the 

 optic nerve very tortuous, and entangled with 

 the ciliary nerves, anastomosing freely with 

 each other. 



The posterior or short ciliary arteries pierce 

 the sclerotic close to the entrance of the optic 

 nerve ; some of their branches are distributed 

 to that membrane in which they anastomose 

 with branches from the muscular arteries ; 

 while all the others advance nearly parallel, 

 dividing at very acute angles into numerous 

 smaller twigs; these branches are at first ex- 

 ternal to the choroid ; but in their course for- 

 wards they penetrate to the internal surface of 

 that membrane, and becoming more numerous 

 from having undergone new subdivisions, form 

 a network of anastomoses from which several 

 branches are sent to the ciliary margin of the 

 iris, where they anastomose with the anterior 

 ciliary, but a greater number are given to the 

 ciliary processes in the centre of which they 

 form a very fine network, and finally end in a 

 circle of anastomoses surrounding the margin 

 of the circle in which these processes terminate 

 internally. 



The long ciliary arteries are two in number, 

 one internal, the other external ; they are larger 

 than the short ciliary arteries among which they 

 arise, but pierce the sclerotic obliquely at a 

 greater distance from the optic nerve ; they 

 pass forwards between the sclerotic and cho- 

 roid, and having arrived at the ciliary ligament, 

 they divide each into two long branches which 

 separate from each other at obtuse angles, and, 

 coursing along the ciliary margin of the iris, 

 form a circle around the greater circumference 

 of that membrane which receives branches of 

 anastomosis from the short ciliary arteries. 

 From the interior of this circle numerous 

 branches arise, each of which divides into two, 

 which diverge at obtuse angles, and, anastomo- 

 sing with each other and with the anterior 

 ciliary, form another arterial circle within the 

 former. Thus there are two arterial circles, one 

 within the other at the greater circumference of 

 the iris. From the concavity of this inner 

 circle the arteries of the iris arise. These arte- 

 ries are very numerous ; they converge in ser- 

 pentine lines towards the papillary margin of 

 the iris, where they anastomose, in the manner 

 of the mesenteric arteries, to form the lesser 



