After passing through the node of the primative groove, the mesoderm and endoderm differentiate, while the of the primitive streak (or groove) elongates anteriorly. The endodermal tissue has spread dorsally, as well as laterally on each side. The “embryo cup" is however still fairly symmetrical at this stage with a fairly even distribution of ectoderm and mesoderm.
Dorsal cross section
Sagittal cross section
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