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Atlas of Human Embryos Chapter   Figure

amnion, cut edge of umbilical vesicle, ectoderm, endoderm, extra-embryonic ectoblast, extra-embryonic mesoblast, lateral body fold, mesoderm, primitive groove, primitive streak, umbilical vesicle cavity, umbilical vesicle roof

A section through the cranial part of the primitive streak and the overlying primitive groove.

Observe:
1. The midline zone of proliferation of ectoderm, the primitive streak.
2. The layer of mesoderm that spreads laterally from the streak.
3. Lateral body folds that cause all three germ layers to arch from side to side.
4. The endodermal layer encroaching on the dorsal part of the yolk sac cavity.


Keywords: amnion, cut edge of umbilical vesicle, ectoderm, endoderm, extra-embryonic ectoblast, extra-embryonic mesoblast, lateral body fold, mesoderm, primitive groove, primitive streak, umbilical vesicle cavity, umbilical vesicle roof

Source: Atlas of Human Embryos.