Primitive streak

Primitive streak
[L. primitus - at first]. Longitudinal cleft formed on surface of amniote blastodisc by a convergence of cells. Gastrulation begins as epiblast cells migrate towards and into the streak.

primitive streak - thickening of the epiblast cell layer caused by movement of mesodermal cells into the blastocoel; this structure is characteristic of avian, reptilian and mammalian gastrulation.

The Primitive Streak; Formation of the Mesoderm."The embryonic disk becomes oval and then pear-shaped, the wider end being directed forward.

primitive streak A medial thickening along the dorsal margin of an amniote embryo that forms during the migration of endodermal and mesodermal cells into the interior of the embryo.

It begins with a "primitive streak" which establishes the anterior and posterior axes and the bilateral symmetry of the body. The neural tube forms from the union of two ridges on the top side.

... into a role for the primitive streak in development of the murine allantois ... During gastrulation, the allantois grows into the exocoelomic cavity as a ...
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thickened ridges of the primitive streak; formed by convergent flow of epiblast.
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In human embryology, formation of neural plate is the first step of neurulation. It is created by a flat thickening opposite to the primitive streak.

The baseline function of axis is demonstrated by two alleles that arrest during formation of the primitive streak. However, two other alleles have a severely disorganized body axis later in development.

See also: Cells, Embryo, Human, Ectoderm, Organ