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.


Formalin Peri Crest Exter 


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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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