In front of the primitive streak two longitudinal ridges, caused by a folding up of the ectoderm, make their appearance, one on either side of the middle line (Fig. 16). These are named the neural folds; they commence some little distance behind the anterior end of the embryonic disk, where they are continuous with each other, and from there gradually extend backward, one on either side of the anterior end of the primitive streak. Between these folds is a shallow median groove, the neural groove (Figs. 17). – See more at: http://www.nexttec.tk/2015/08/the-neural-groove-and-tube.html#sthash.pUkguqx3.dpufThe Neural Groove and Tube | The Next Technology.