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primitive streak


Definition: ridge of epiblast in the midline at the caudal end of the embryonic disc from which arises the intraembryonic mesoderm and definitive endoderm; achieved by inward and then lateral migration of cells; in human embryos, it appears on day 15 and provides visual evidence of the cephalocaudal axis.

Synonym(s): gastrulation streak, germinal streak

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© Copyright 2018 Wolters Kluwer. All Rights Reserved. Review Date: Sep 19, 2016.