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Developmental Anatomy

Stage 23: Summary

First view Second view

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.

Lab Manual - Horizon 23 (CC#4570)

First view Second view Third view

  • 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.

Stage 23: Animation

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

Stage 23 (PDF 96 KB)

 

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