Changes

==Gastrulation at the Node==

==Gastrulation at the Node==

*The primitive streak stops elongating at about 75% of the way along the length of the posterior - anterior axis.  

The primitive streak stops elongating at about 75% of the way along the length of the posterior - anterior axis. Cells condense at this anterior point of the primitive streak and continue to proliferate; called '''Hensen's Node'''. They then ingress and replace the anterior hypoblast and form foregut endoderm. Cells then migrate anteriorly, leaving the node. These cells will form all of the head mesoderm. The node then regresses posteriorly, destroying the primitive streak and forming the '''notochord''' (axial mesoderm). The notochord begins at the level of the midbrain. Notochord regression also produces paraxial mesoderm. Anterior cells are developing before posterior cells have undergone gastrulation.

**Cells condense at this anterior point of the primitive streak and continue to proliferate; called '''Hensen's Node'''.

**They then ingress and replace the anterior hypoblast and form foregut endoderm.

**Cells then migrate anteriorly, leaving the node. These cells will form all of the head mesoderm.

***The node then regresses posteriorly, destroying the primitive streak and forming the '''notochord''' (axial mesoderm).

***The notochord begins at the level of the midbrain.

***Notochord regression also produces paraxial mesoderm.

****Anterior cells are developing before posterior cells have undergone gastrulation.

==Gastrulation at the Tail Bud==

==Gastrulation at the Tail Bud==