This is a 3µm transverse slice (#35) of the rat E10 egg cylinder.  Surrounding uterine tissue is not in the picture.  The slice cuts the anterior part of the embryo on the left (with the neural groove in the midline of the future brain) and a posterior part on the right (with the neural plate of the future spinal cord).  A layer of cuboidal cells, most likely surface ectoderm, is in between.  The amnion and yolk sac are no longer in the slice.