This section is from the book "Anatomy Of The Arteries Of The Human Body", by John Hatch Power. Also available from Amazon: Anatomy of the Arteries of the Human Body, with the Descriptive Anatomy of the Heart.
The Ciliary Arteries are divided into three sets,—the short, the long, and the anterior,—and at their origins correspond to the upper surface of the optic nerve. The short ciliary arteries (twenty, thirty, or sometimes even forty in number) advance tortuously through the fatty matter that envelopes the optic nerve, around which they form a vascular net-work. After frequent anastomoses they penetrate the sclerotic coat, near the entrance of the optic nerve; some few of them terminate in this membrane, the rest proceed between the sclerotic and choroid coats. After forming by their frequent subdivisions and anastomoses a kind of vascular net-work on the exterior of the choroid, they pierce this membrane, and form an expansion of more minute vessels on its interior. Having arrived at the ciliary body, some of them merely pass through it to arrive at the great arterial circle of the iris, but by far the greatest number terminate in the ciliary body, each ciliary process receiving so many as twenty or thirty branches: these take a tortuous course in the substance of the processes, and then, reuniting into larger and fewer branches, terminate behind the iris by anastomotic arches. In most cases several of these ciliary arteries come from some of the principal branches of the ophthalmic, and not directly from its trunk. The long ciliary arteries, usually two in number, pierce the sclerotic coat a little in front of the short ciliary, and then run from behind forwards between the sclerotic and choroid coats; one on the inner side, and the other on the outer side of the eye. In this course they send a few delicate branches to the sclerotic coat, and still fewer to the choroid; and having arrived at the ciliary body they subdivide into many branches, which communicate with the short ciliary arteries and form an arterial circle at the ciliary margin of the iris. From this circle arise many small branches, which proceed towards the pupil in a radiated, manner, and then bifurcate and anastomose with adjacent branches, so as to form a second arterial circle within the first. From this second circle arise smaller and more numerous branches than from the first; these proceed in a radiated manner to the pupillary margin of the iris, where most of them enter into the formation of a third arterial circle within the two preceding. In every instance the muscular arteries give off several ciliary branches, which have been termed the anterior ciliary: these pierce the anterior part of the sclerotic coat, and communicate with the preceding. In speaking of the vascularity of the iris, Dr. Jacob observes:—" Much importance has been attached by anatomists to the manner in which these radiating vessels are disposed, in consequence of the representation of Euysch, who exhibited them as forming a series of inosculations at a short distance from the pupil, since called the lesser circle of the iris.
I do not deny that the vessels of the iris inosculate as in other parts of the body, but I do not believe that they present this very remarkable appearance, and I suspect that Ruysch exaggerated what he had seen, or described from an iris in which the injection had been extravasated and entangled in the tendinous cords, which I have described as extending from the fleshy bodies to the margin of the pupil. The question is fortunately of no importance. It is sufficient to know that the organ is amply supplied with arterial blood."* In the foetus, branches of the long ciliary arteries may be traced to the membrana pupillaris. In the operations of couching, the needle should be made to penetrate the eye below its centre, in order to avoid these vessels.