Fig. 9. Composite illustration to scale of the various vascular arrangements. Venous vessels and superficial central retinal artery (CRA) plexus are not drawn in full. Retrolamina: 1, Pia mater as source of transverse and longitudinal vessels. 2,2', Recurrent short posterior ciliary artery (SPCA) to retrolamina, and pial vessels to lamina cribrosa. 3,3', Pia-derived longitudinal arterioles course to and anastomose with laminar vasculature. 4, Occasional realized large pial arteriole courses longitudinally through laminar tissue. 5, Intraneural branching of central retinal artery, with anastomosis to laminar and retrolaminar systems. Lamina cribrosa: 6, Transverse entry of scleral short posterior ciliary arteries that dominate laminar vasculature and mingle with longitudinal microcirculation. Prelamina: 7, Branch of short posterior ciliary artery courses through Elschnig's tissue (E) at level of choroid (CH) and enters into nerve. 8, Occasional choroidal vessel to prelamina; S, sclera. Superficial nerve fiber layer (SNFL): 9, Choriocapillaris “spur” capillary anastomoses with other retinal and prelaminar vessels. 10, Both epipapillary and peripapillary branches of central retinal artery anastomose with prelaminar vessels. (Lieberman MF, Maumenee AE, Green WR: Histologic studies of the vasculature of the anterior optic nerve. Am J Ophthalmol 82:405, 1976)