Formation of the ocular arteries in the chick embryo: observations of corrosion casts by scanning electron microscopy.

An investigation was carried out on the formation of the blood vessels that supply the optic cup or eyeball in developing chick embryos ranging in age from Hamburger-Hamilton stage 17 (st17) to st44. Corrosion casts of the vasculature were made by injecting resin and examined by scanning electron microscopy. The optic cup was supplied by branches of the cranial ramus of the circle of Willis (CCW) from st17 to st19. By st23, a branch of the CCW and that of the internal carotid artery became anlagen of two ophthalmic arteries, namely, the cerebral ophthalmic artery (COA) and the internal carotid ophthalmic artery (ICOA) respectively. They were continued by primordia of the long posterior ciliary arteries, which connected with each other to form a ring around the pupil. Between st19 and st26, another branch of the CCW was found, by contrast, to supply the primitive pecten. The distal part of the nasal long posterior ciliary artery began to atrophy at st28, so the temporal long posterior ciliary artery only began to supply the ring artery around the pupil by st30. At the same time, the artery supplying the pecten became anastomosed with the ICOA behind the eyeball to form the definitive pectinate artery. By st30, the ophthalmic branch of the stapedial artery had also formed and connected with the distal part of the ICOA behind the eyeball, as well as with the distal part of the COA by st34. The supraorbital branch of the stapedial artery, which had replaced the CCW to anastomose with the ethmoidal artery by st30, was found to be connected to the COA at st36. The main vascular system supplying the eyeball was complete at st36, and its structure at st40 and st44 was fundamentally similar to that at st36.