Formation and Closure of Anterior Neuropore
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.
KeywordsFormalin Peri Crest Exter
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