Structure of the midterm placenta of the spotted hyena, Crocuta crocuta, with emphasis on the diverse hemophagous regions.

The hyena placenta is unique among carnivores in being hemochorial. It also has areas of erythrocyte uptake that differ from those seen in more commonly studied carnivores. The availability of timed midterm pregnancies made it possible to examine the organization of the placenta, the distribution of regions of columnar trophoblast and the nature of the heterophagous and hemophagous regions in well-preserved material. The labyrinth of the placenta is orderly arranged with periodic primary villi that have a surface of syncytial trophoblast. Secondary projections from the primary villi anastomose extensively. The junctional extreme of each primary villus forms an expanded tip covered by columnar trophoblast cells. Marginal to the hemochorial placenta, the paraplacenta is exposed to varying amounts of extravasated maternal blood which the cytotrophoblast cells ingest and destroy. Columnar trophoblast cells at the tips of the primary villi, in the villi of paraplacental margins of the labyrinth, in isolated patches within the labyrinth and beneath the allantochorionic plate are all capable of and are variably involved in erythrophagocytosis. Variations in the structure and the lectin histochemistry of the columnar trophoblast cells indicate variation depending on the exposure of these cells to erythrocytes and/or other histotrophic materials. The widespread distribution of the hemophagous regions suggests a nutritive function in addition to an iron transfer function of the columnar cytotrophoblast.