Intro

We begin with a view of the female reproductive tract, oriented so that you are within the peritoneal cavity and looking inferiorly onto the surface of these structures.  Visible in the center is the uterus, from which the Fallopian, or uterine, tubes travel laterally to reach the ovaries.

As we progress through the wall of the uterus, we enter the uterine cavity.  Note here that you are now within a space that is continuous with the outside via the vaginal canal.  The inner surface of the uterus is now visible.

Toward the end of its first week of development, the embryo was freely floating within the lumen of the uterus, just as you are now.  Around day 6, the embryo made contact with the epithelial surface you are seeing, and, over the course of several days, burrowed through the epithelium and into the underlying connective tissue of the endometrium.  The epithelium eventually resealed, so that the bulge you see is due to the embryo growing within the endometrium.

Removal of the endometrial epithelium and connective tissue overlying our embryonic structures reveals the developing placenta, with the chorionic villi shown.

Removal of a portion of the placenta exposes the chorionic cavity, or extraembryonic coelom.  Within this cavity, the embryo is seen attached to the inner surface of the placenta by a connecting stalk.  At this point, which is toward the end of the third week of the embryo’s development, the clearly visible structures attached to the connecting stalk are the amnion and yolk sac.  The embryo is a disk-shaped structure between these two cavities.