Formation and Closure of Anterior Neuropore

9 Days, 13–20 Somites
  • Karl Theiler


This period could be extended to 22 somites, because the most advanced embryo, with a copulation age of 9 days 2 hours, had 23–24 pairs of somites. In the mouse, the formation of a new somite pair requires 1–2 hours. I have chosen an upper limit of 20 somites for this stage so that it will correspond to Streeter’s horizon XI.


Neural Tube Umbilical Artery Coelomic Epithelium Trophoblastic Giant Cell Uterine Lumen 
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Copyright information

© Springer Science+Business Media New York 1989

Authors and Affiliations

  • Karl Theiler
    • 1
  1. 1.Department of AnatomyUniversity of ZurichZurichSwitzerland

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