 In this video we are going to have a quick look at what the human embryo looks like around 14 days post conception. By this stage it is embedded or implanted in the endometrium of the uterus. We have already removed that surrounding tissue, so the first thing we see is this, the Sincitio troughoblast. Beneath that is the Cytotrophoblast. Together these two become the interface between the mother and the embryo. The most important part of this being the placenta. Beneath the Cytotrophoblast is this tissue called extraembryonic mesoderm. If we remove that layer we see a space known as the extraembryonic ceilum. You can see how the extraembryonic mesoderm in purple has formed this connection here called the connecting stalk. The extraembryonic mesoderm then covers the embryo in the middle here as well. So the extraembryonic ceilum is a space between these layers of extraembryonic mesoderm. Inner attached to the embryo proper. Outer attached to the cytotrophoblast. Let's take a look at all that in cross-section now. So this layer of extraembryonic mesoderm plus the cytotrophoblast and the Sincitiotrophoblast. These three together are known as the chorion. The extraembryonic ceilum also goes by the name of chorionic cavity which is really a much better name because it accurately describes what it is the space beneath the chorion. This inner layer of extraembryonic mesoderm covers the core of the embryo which consists of two flat disks and two spaces above and below. Together these two are known as the bilaminar disk which literally just means two layered disk and they're individually known as the epiblast and the hypoblast. The cells of the epiblast transform into the three layers of cells that become the bulk of the human body. For more information on that process watch our video on the first three weeks. This space here is the amniotic cavity and this is the yolk sac. The yolk sac has this little pouch here known as the alantoir. It becomes an important part of the umbilical cord. Click the link below to play around with this model yourself. I hope you found this video useful. Click like if you did and we will see you next time.