Development of the notochord in a stage 8 (17–19 days) human embryo.

From left to right transversal illustrations, a schematic ventral view, transversal sections from specimen No. 7545 and a ventral view of a 3D reconstruction of specimen No. 5960. The embryo is viewed from ventral with the endoderm removed. Black lines indicate the level of the transversal sections (epiblast/ectoderm is superior in each transversal section). Subsequent to the gastrulation area (purple) the notochordal process (cyan blue) with a neurenteric canal (white on the schematic view and black arrow in the transversal sections) is present. The notochordal process is round, but further cranial it becomes smaller and the endoderm on its ventral side is hard to distinguish. Cranial in the embryo, the prechordal plate (brown) emerges as a cluster of mesenchymal cells. The prechoral plate can be identified in the 3D reconstruction as a broader structure cranial to the notochordal plate. Endoderm: light grey (in cross sections), epiblast or ectoderm: dark blue, dark grey (in transversal sections), gastrulation area (GA): purple, neurenteric canal: white, notochordal plate (NPL): yellow, notochordal process (NPR): cyan blue, prechordal plate (PP): brown.