Electron microscopic study of the chorioallantoic placenta of the rock hyrax (Heterohyrax brucei).
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The interhaemal membrane consisted of only two cellular elements: a single layer of cellular trophoblast and the fetal capillary endothelium. The hyrax is therefore one of the few mammals known to possess the cellular haemomonochorial type of placenta. The trophospongium was also cellular while the basal trophoblastic cells were strongly phagocytic. The giant multinucleate cells at the feto-maternal junction were ultrastructurally different from the trophoblast cells and showed no signs of degeneration. Their appearance suggests that they are of maternal rather than fetal origin