FIGURE 8-5 Formation of the Neural Tube A long depression, the neural groove, first forms in the neural plate. By day 21, the primitive brain and neural groove are visible. On day 23, the neural tube is forming as the neural plate collapses inward along the length of the embryo’s dorsal surface. The embryo is shown in a photograph at 24 days.

Prof. P.M. Motta/Science Source