The chorioallantoic placenta of the spotted hyena (Crocuta crocuta Erxleben): an electron microscopic study

The histology and ultrastructure of the chorioallantoic placenta of the spotted hyena have been studied in three specimens obtained in the field and fixed promptly with glutaraldehyde. Observations revealed that the interhemal membrane at its minimal thickness is hemomonochorial, consisting of a continuous layer of syncytial trophoblast, a basal lamina, and fetal capillary endothelium. Cytotrophoblastic cells form a discontinuous layer beneath the syncytial trophoblast and are distinguished by the presence of numerous extracted lipid droplets in their cytoplasm. A network of extracellular spaces, incorrectly identified as cisternae of endoplasmic reticulum by earlier investigators, occurs beneath the maternal surface of the syncytial trophoblast. These spaces contain moderately dense, nonfibrillar material resembling the intrasyncytial lamina previously described only in the hemochorial placenta of certain bats. Hence, these spaces may contain remnants of maternal capillary basal lamina following displacement of the endothelium by extensions of syncytial trophoblast at an early stage of placental development.