This is a 3µm longitudinal slice (#9) of the left side of the rat E10 egg cylinder. All of the structures in this slice are similar to the previous slices. The long curved line separated by perpendicular hatch marks indicates the neuroepithelium and the contiguous surface ectoderm. The anterior neuroepithelium is folding forward into a hook. The anterior face of the hook may be future forebrain. The hump area is probably the future midbrain (which has a prominent similar flexure in the mature brain). The posterior concave bend marks the site of the future hindbrain (pons and medulla). All of these hatchmarks are my suggestions of regions, and should not be interpreted as absolute boundaries. The slice does not yet cut through the spinal cord, but only through more lateral parts of the future brain.