FORNICATE STRUCTURE OF BLIND-ENDING LYMPH ATIC SEGMENTS IN CONJUNCTIVA - SCANNING ELECTRON-MICROSCOPY STUDIES

Background The accepted fundamental element of the initial lymphatic s ystem is a tubular structure (lymphatic capillary), which is present e ither in the form of a finger-shaped blind-ending protuberance, or in the nature of a plexiform composite arrangement. We were able to demon strate experimentally that the finger-shaped protuberances, which are known as ''initial segments'' are in fact temporary filling states. As the filling process continues, these vascular elements become interme diate segments, via which other parts of the vascular network take up the dye. To date there have been no investigations of the internal str ucture of these apparently blind-ending vessel segments. In this study , lymphographically represented ''terminal segments'' should be cut aw ay for the purpose of examining the fornix by scanning electron micros copy. Is the internal surface of the fornix regular and unbroken, or a re there fissure-like structures which could explain the observed fill ing processes? Material and methods In conjunctiva of bovine eyes (n = 80), interstitial double-contrast lymphography (Berlin-blue solution/ air) under a slit-lamp microscope was used specifically to search for finger-shaped terminal segments. The conjunctivae had previously been prepared by fixing in polymeric resins. A proportion (n = 21) of the s pecimens were amenable to examination under the scanning electron micr oscope. Results Nothwithstanding the observed great variation in the s hape of the lymphographically obtained blind-ending structures - in th e form of terminations shaped variously like fingers, balloons, domes, pistons or pyramids, terminations with two humps, and terminations sh aped like spear heads scanning electron microscopy revealed within the fornices many relatively uniformly shaped structures in the form of f issures, configured with lips and saw-tooth edges, rather like zip fas teners. These findings are suggestive of preformed connections to neig hbouring segments. This appears to be another element, in addition to the familiar flap-like structures, for controlling the circulation of lymph. Does the ''initial part'' of the lymphatic system now have to b e redefined?