File:Human embryo day 18.jpg

From Embryology

Original file(531 × 800 pixels, file size: 80 KB, MIME type: image/jpeg)

Human Embryo (day 18)

Approximate cross-section of a different, 18 day human conceptus (Carnegie stage 6).

Identify the

  • 3 cavities - yolk sac, amniotic sac and chorionic sac.
  • 3 layers of the trilaminar embryo - ectoderm (columnar cells), intraembryonic mesoderm (mesenchymal cells, endodermal cells (cuboidal single layer).
  • extraembryonic mesoderm which surrounds the yolk and amniotic sacs, and continues to form the connecting stalk, where it then continues to line the chorionic sac. Extra- and intra-embryonic mesoderm merge along the perimeter of the embryonic disc.
  • primitive groove with dense cluster of primitive streak cells below it.

At the top right of the micrograph is a secondary chorionic villus, lying in an empty maternal intervillus space. The villous has an outer layer of syncytiotrophoblast (smaller, darker nuclei), an intermediate layer of cytotrophoblast and a core of mesoblast (extra-embryonic mesoderm).

Links: Carnegie stage 6


Nishimura etal., 1977

Cite this page: Hill, M.A. (2024, June 18) Embryology Human embryo day 18.jpg. Retrieved from

What Links Here?
© Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G

File history

Yi efo/eka'e gwa ebo wo le nyangagi wuncin ye kamina wunga tinya nan

current21:48, 8 October 2015Thumbnail for version as of 21:48, 8 October 2015531 × 800 (80 KB)Z8600021 (talk | contribs)
20:38, 9 May 2010Thumbnail for version as of 20:38, 9 May 2010398 × 600 (38 KB)S8600021 (talk | contribs)Human embryo day 18 Category:Week 3