BLOOD-VESSELS OF THE IRIS. 723 



the whole length of each ciliary process, and communicates through inter- 

 veuing vessels with a long venous trunk which runs a similar course on the 

 attached surface. 



Fig. 469. 



Fig. 469. INJECTED BLOOD-VESSELS OF THE CHOROID COAT (from Sappey). & 



1, one of the larger veins ; 2, small communicating vessels ; 3, branches dividing into 

 the smallest vorticose vessels. 



Arteries of the iris. The special arteries of the iris are the long ciliary 

 and the anterior ciliary. 



The long (posterior) ciliary arteries, two in number, and derived from the ophthal- 

 mic, pierce the sclerotic a little before, and one on each side of, the optic nerve. 

 Having gained the interval between the sclerotic and choroid coats, they extend 

 horizontally forwards through the loose connective tissue (membrana fusca) to the 

 ciliary muscle. In this course they lie nearly in the horizontal plane of the axis of the 

 eye-ball, the outer vessel being however a little above, and the inner one a little below 

 the level of that line. A short space behind the fixed margin of the iris each vessel 

 divides into an upper and a lower branch, and these, anastomosing with the corre- 

 sponding vessels on the opposite side and with the anterior ciliary, form a vascular 

 ring (circulus major) in the ciliary muscle. From this circle smaller branches arise 

 to supply the muscle; whilst others converge towards the pupil, and there, freely com- 

 municating by transverse offsets from one to another, form a second circle of anasto- 

 mosis (circulus minor], and end in small veins. 



The anterior ciliary arteries, five or six in number, but smaller than the vessels 

 just described, are supplied from the muscular and lachrymal branches of the ophthal- 

 mic artery, and pierce the sclerotic about a line behind the margin of the cornea ; 

 finally, they divide into branches which supply the ciliary processes, and join the 

 circulus major. 



Besides these special arteries, numerous minute vessels enter the iris from the ciliary 

 processes. 



The veins of the iris follow closely the arrangement of the arteries just 

 described. The circular sinus communicates with this system of vessels. 



3 B 2 



