First, the embryo is a flat blastodisk that undergoes thickening at the posterior end.
The embryonic axis starts to form from the middle of this overhang and elongates
from the posterior to the interior.
The neural plate appears anteriorly, the neural folds close together and the
anterior neuropore narrows to close.
At this stage, several pairs of somites are visible.
If we look at the lateral side of the embryo, we can see the optic vesicle,
the formation of the pharyngeal cleft, and the formation of the otic placode.