Development of the neural tube in human embryos (Prentiss-Arey).  A.  An early embryo (Keibel)  B. at 2 mm. (Graf Spee)  C. at 2 mm. (Mall)  D. at 2.7 mm (Kollmann).
This is a scan of Figure 6 of the book "The anatomy of the nervous system" by Stephen Walter Ranson, with the labels redrawn.
user:Looie496 created file, original artist unknown
file created 2009-12-24, original image published 1920
<bdi><a href="https://www.wikidata.org/wiki/Q28854874" class="extiw" title="d:Q28854874"><span title="American neurologist">Stephen Walter Ranson</span></a>
</bdi>