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Stage 9 embryos have a greatest length of 1.4 to 2.5 mm and an estimated postfertilization age of approximately 25 to 27 days. The somite period begins with the formation of one to three somites. The pro- mes- and rhomb- encephalon can be identified in the cephalic part of the neural folds. The pericardial cavity is present for the first time and the right and left ventricles and right and left atria can be identified by their positions. The dorsal aorta, aortic arch arteries and umbilical vessels are present.


New structures include conotruncus, foregut, heart, hepatic plate endoderm, rhombomere A, somite 1 (O-1).

Section 45

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Dorsal view

Dorsal view

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