Fig. 15.Coronal section of the anterior hypothalamus in a human fetus of gestational age 12-14 weeks, counterstained with methylgreen and thionine. (A) Note that from the wall of the third ventricle, constituting the ependymal layer of the neural tube, a front of developing cells (arrows) migrate laterally towards the mantle layer to give rise to the primordium of the paraventricular nucleus (PVN). (B) High magnification of the image included in the rectangle shown in A. Note the high cellular density in the ependymal layer (EL) of the neural tube contrasts with the more diffuse distribution of migrating neuroblasts in the developing mantle layer (ML). III = third ventricle.