Gastrulation summarized

paired neural folds future brain yolk sac embryonic disk primitive streak amniotic cavity chorionic cavity neural groove (below, notochord is forming) somites A Day 14 Gastrulation begins. A B Day 16 Neural groove C Days 18—23 Bumps of mesoderrn depression called the primitive streak appears as the neural (somites) form. They will develop into the appears on the embryonic disk. tube begins forming. dermis and most of the axial skeleton. pharyngeal D Days 24—25 Pharyngeal arches develop. They will contribute to the face, neck, larynx, and pharynx.