This is a 3µm transverse slice (#55) of the rat E10 egg cylinder.  Surrounding uterine tissue is not in the picture.  The slice is near the bottom of the U-shaped embryo and cuts through a thick ring of neuroepithelium that falsely gives the impression of a neural tube.  Notice the greater narrowing of the embryonic cavity from slice #50.  The notochordal plate is now present beneath the neural groove both anteriorly and posteriorly.  The mesoderm is very thick and compact on lateral sides of the neuroepithelium.