UNSW Embryology

Carnegie Stage 12

© Dr Mark Hill (2009)

Acknowledgements

Carnegie Stage 12 Facts: Week 4, 26 - 30 days, 3 - 5 mm, Somite Number 21 - 29 View: Lateral view, day 26, 27 somites, Amniotic membrane removed. Stage 12 SEM Features: day 26, 27 somites, forebrain, site of lens placode, site of otic placode , stomodeum, 1st pharyngeal arch, 2nd pharyngeal arch, 3rdpharyngeal arch, heart prominence, somite Identify: forebrain, site of lens placode, site of otic placode, stomodeum, 1st pharyngeal arch, 2nd pharyngeal arch, 3rd pharyngeal arch, heart prominence, somite Next:

Events

Ectoderm: Neural tube continues to close, Caudal neuropore closes, forebrain

Mesoderm: continued segmentation of paraxial mesoderm (21 - 29 somite pairs), heart prominence

Head: 1st, 2nd and 3rd pharyngeal arch, forebrain, site of lens placode, site of otic placode, stomodeum

Body:

heart, liver, umbilical, early upper limb bulge

Fetal Membranes

Stage 12 embryo with 2 fetal membranes visible. The embryo is lying inside its closely fitting amniotic sac which lies inside the much larger chorionic sac. The yolk sac cannot be seen in this particular image.

Outside the chorionic sac highly-branched tertiary chorionic villi can be seen.

Note yolk sac stalk and body stalk are separate structures, i.e., the umbilical cord has not yet formed.

(Image from Blechschmidt, 1974)

Next - Carnegie Stages 13

Stage 13 Unlabelled | Stage 13 Labelled

Glossary of Terms

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Carnegie Stage images

The Kyoto Collection images are reproduced with the permission of Prof. Kohei Shiota for tutorial/revision purposes and cannot be reproduced electronically or in writing without permission.

UNSW Embryology ISBN: 978 0 7334 2609 4

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