|Diagram showing the expansion of amnion and delimitation of the umbilicus.|
|Section through the embryo.|
|Gray's||subject #10 53|
The caudal end of the embryo is at first connected to the chorion by a band of mesoderm called the body-stalk, but with the formation of the caudal fold the body-stalk assumes a ventral position; a diverticulum of the yolk-sac extends into the tail fold and is termed the hind-gut.
The function of the body-stalk is later replaced by the umbilical cord.
Human embryo—length, 2 mm. Dorsal view, with the amnion laid open. X 30.