Long posterior ciliary arteries

There are 2 long posterior ciliary arteries, which arise at the base of the orbit from the external ohptalmic artery or its anastomotic branch with the internal ophthalmic artery. They join the eyeball, placed medially and laterally to it, and follow its horizontal meridian, gradually penetrating the sclera. They give rise to various choroidal vessels along the way, before reaching the iris, where they form the major circulus arteriosus of iris. Depending on the species, they may give rise to cilioretinal arteries, muscular branches, episcleral arteries and/or branches for the ciliary body at different points in their trajectory.