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HH04- (early) |
The circular outline of Hensen's node becomes visible, but no pit. Mesoderm visible lateral to the streak. |
HH04 |
(18-19 hours) Primitive streak grooved, -1.88 mm long. Hensen's node present. A distinct circular pit exactly at the centre of Hensen's node becomes visible. Mesoderm visible lateral to the streak. Area pellucida pear-shaped. |
HH04+ (late) | The emerging notochord (head process) is visible as a small triangular protrusion above Hensen's node. |