Primitive Streak

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primitive streak

[′prim·əd·iv ′strēk]
A dense, opaque band of ectoderm in the bilaminar blastoderm associated with the morphogenetic movements and proliferation of the mesoderm and notochord; indicates the first trace of the vertebrate embryo.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Primitive Streak


a longitudinal thickening of the outer layer of the embryonic disk, or blastodisk, in the embryos of birds, mammals, and humans; it is formed during the process of gastrulation. Mesodermal cells migrate from the primitive streak to the area between the ectoderm and endoderm. These cells later form the somites and lateral plates. In the anterior end of the primitive streak, the cell accumulation known as Hensen’s node develops. This cellular material becomes the notochord.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.