Progressive neuronal differentiation in the submandibular ganglia of a series of human fetuses

Serial sections of a series of 20 human fetuses, ranging in age from 4+ weeks (6 mm C.R.) through full term (470 mm C.H.) were studied from the standpoint of progressive development changes in the the submandibular ganglion neuroblasts. The basic staining technique used was the silver nitrate method of Holmes, with luxol fast blue, toluidine blue, gallocyanin and H&E employed as alternate counterstains. General topography and the formation of roots in relation to the developing ganglion were studied. Morphological changes in the neuroblasts were related to time of first appearance in the series. Neuroblasts were easily distinguished from non‐nervous ganglion cells at the 79 mm stage. Neuroblastic multipolarity was present at the 79 mm stage also, and the cells were predominantly multipolaar at the 278 mm stage. Neurofibrillae, Nissl bodies, well‐formed capsules and the reduction of the number of nucleoli to one or two were characteristics first observed in the 120 mm fetus. Preganglionic terminal arborizations were observed as early as the 25 mm stage. Counts of ganglion neuroblasts of four selected fetuses indicated a progressive reduction in numbers from 12,128 at 17 weeks (120 mm) to 5,988 at full term. Measurements of ganglion neuroblasts of four selected fetuses revealed a progressive increase in the cytoplasmic/nuclear ratio from 1.38 at 15 weeks (97 mm) to 2.05 at full term.