External: The head has made rapid progress in its bending toward the erect position. The head is distinctly rounded out, and the cervical region and trunk are of a more mature shape. The eyelids may show some fusion laterally and medially, but the eyes may be largely open.

• Length 28-30 mm
• In the terminal horizon the head has made rapid progress in its bending toward the erect position.
• Other transformations include a distinct rounding out of the head and a more mature shaping of the neck region and the body.
• The extremities have markedly increased in length and show advancement in the differentiation of their subdivisions.
• The forearm rises upward to or above the level of the shoulder.
• The scalp plexus is rapidly approaching the vertex of the head, leaving only a small nonvascular area which will soon become bridged by anastomosing branches.
• Ovulation age: 56-60 days

Question: What will happen to the small nonvascular area of the head?

Developmental Stages in Human Embryos by Ronan O'Rahilly and Fabiola Müller.  Published by Carnegie Institution of Washington, Publication 637. 1987. Stage 23 (PDF)

Stage 22

Animations Stage 23 Internal