Extra-embryonic mesoderm/Extra-embryonic coelom
- Cells derived from the primitive ectoderm fill the space between the trophoblast and two cavities
- This loose connective tissue, the extraembryonic
mesoderm, completely surrounds the amnion
and primary yolk sac
- Fluid-filled spaces appear in the mesenchyme, pushing aside
the mesenchyme to form a coelom
- These spaces fuse to form a fluid-filled cavity completely
surrounding the amnion and yolk sac, except at the connecting
stalk
Key: The forming extraembryonic coelom
(dark blue) shows a few remaining extra-embryonic mesoblasts,
demonstrating that it originated from spaces forming and then
coalescing.
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