Chorionic Ectoderm Cells (ChB)

The chorionic ectoderm cells develop from the extraembryonic ectoderm and form the ectodermal layer of the chorion bilayer at 7.5 dpc. They are complemented by mesodermal cells from the epiblast-derived extraembryonic mesoderm, which make up the inner layer of the bilayer. At 8.5 dpc, the chorion bilayer fuses with the allantois resulting in the chorioallantoic placenta (the fetal portion of the placenta).