34 



HISTOGENESIS 



Neural cresl 



Ectoderm 



Neural crest 



fMesodermal segment 



FIG. 309. Three stages in the development of the ganglion crest in human embryos (after von 



Lenhossek in Cajal). . 



FIG. 310. Stages in the formation of unipolar ganglion cells (Cajal). From a 44 mm. human 



fetus. 



