McMenamin P G, Krause W J
Department of Anatomy and Human Biology, University of Western Australia, Nedlands.
Cell Tissue Res. 1993 Mar;271(3):461-8. doi: 10.1007/BF02913728.
Light-microscopic and ultrastructural analysis of the ocular tissues of the North American opossum (Didelphis virginiana) revealed that the arterial and venous segments of retinal vessels, including capillaries of the smallest calibre, occur in pairs. They do not form anastomotic networks, the common pattern in mammals with vascularised retinae, but instead the two segments of the pair join to form hairpin end loops. The paired vessels, with the arteriolar limb usually on the vitread aspect, penetrate the retina and branch to form three distinct layers of capillaries. The most superficial lies in the nerve fiber layer, the middle is situated in the inner nuclear layer and the deepest extends to the external limiting membrane, which is considerably deeper than in normal mammalian holangiotic retinae. The paired capillaries display classical morphological features of central nervous system capillaries, i.e., they are lined by continuous endothelial cells united by tight junctions. The lining endothelium is supported by a distinct basal lamina that splits to envelop pericytes. The latter, although abundant, are invariably interposed between the two vessels that form each vascular unit. Phylogenetic and functional aspects of this unique form of retinal vascularisation are discussed.
对北美负鼠（弗吉尼亚负鼠）眼部组织进行的光学显微镜和超微结构分析显示，视网膜血管的动脉段和静脉段，包括最细口径的毛细血管，都是成对出现的。它们并不形成吻合网络，而有血管化视网膜的哺乳动物的常见模式是形成吻合网络，相反，成对的两段血管会连接形成发夹状终环。成对的血管，其小动脉分支通常位于玻璃体一侧，穿透视网膜并分支形成三层不同的毛细血管层。最表层的位于神经纤维层，中间层位于内核层，最深层延伸至外界膜，这比正常哺乳动物全血管化视网膜中的外界膜要深得多。成对的毛细血管呈现出中枢神经系统毛细血管的典型形态特征，即它们由通过紧密连接相连的连续内皮细胞排列而成。衬里内皮由一层独特的基膜支撑，该基膜分裂以包裹周细胞。后者虽然数量众多，但总是夹在形成每个血管单元的两条血管之间。本文讨论了这种独特的视网膜血管化形式的系统发育和功能方面。
