Brains II

As the infolding lower line now a groove (neural groove) develops the upper head end (bigger than the leg end) also becomes a deep groove affair but more by outgrowth expansion than by downward plunge. From end to end we have an ectoderm strip that is now U shaped. Middle of the tube joins the U at the back surface to form an O. That joined bit begins a zipper process that turns the ectoderm into a tube. In the process that mesoderm has been forming along the sides of the ectoderm/notocord as segments (shown above a muscle color but there is still ectoderm (the skin part) covering it. This muscular segmentation is between the slices Skinand endoderm. Doesn’t the endoderm get to play in this symphony? Yes. Again the notocord tells the nearby endoderm to form gut. (not lip nor butt, but all rest between). [mostly, kinda sort of].

Above are a few moe angles of view with a cross section of events so far. On right notice that muscular mesoderm is capturing within it’s domain a part of the yolk. The boundary is called THE BELLY BUTTON.