External: 4-12 pairs of somites; fusion of neural folds is imminent or in progress; the opic sulcus may have appeared; pharyngeal arch 1 begins to be visible on the surface.

Internal: the cardiac loop is appearing; the laryngeotracheal sulcus develops; the intermediate meso-derm becomes visible

Stereo View

• Length: 1.5 - 3 mm
• 4 -12 pairs of somites.
• Fusion of neural folds is imminent or in progress.
• The optic sulcus may have appeared.
• Pharyngeal arch 1 begins to be visible on the surface.
• The cardiac loop is appearing.
• The laryngeotracheal sulcus develops.
• The intermediate mesoderm becomes visible.
• Ovulation age: 22 - 23 days

Question: What is the state of the neural folds?

Developmental Stages in Human Embryos by Ronan O'Rahilly and Fabiola Müller.  Published by Carnegie Institution of Washington, Publication 637. 1987. Stage 10 (PDF)

Stage 9

Stage 11 Stage 10 Internal