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HH03 | (12-13 hours) Primitive streak extends to centre of embryo; streak is broad throughout and parallel-sided. No groove. Hensen's node not yet discernible. No mesoderm yet visible outside the streak itself. |
HH03+ (late) |
Streak becomes thinner, with a distinct groove along the midline which may not reach the bottom and/or top. Some mesoderm may be visible just outside the streak, starting to emerge laterally. Hensen's node not yet discernible. |