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Implantation site in cleared celloidin block

View of the implantation site as seen in the cleared celloidin block. Endometrial glands and fissures are faintly seen as lighter areas, streaks, and circles. The irregular dark circle is due to maternal blood within the trophoblast lacunae. This accurately outlines the embryo with the exception of a thin, peripheral shell of syncytiotrophoblast surrounding the maternal blood. The occasional areas of hemorrhage and congested vessels in the surrounding endometrium appear as dark splotches and irregular curved dark lines, respectively.

Fig. 12. Hertig and Rock, 1941.

Keywords: endometrial gland, endometrium, implantation site, syncytiotrophoblast, trophoblast lacunae

Source: The Virtual Human Embryo.