Electron Microscopic Studies on the Developing Telencephalic Wall of the Rat Fetus

The dorsolateral wall of th e telencephalon of the rat fetus was studied electron microscopically from day 13 to 22 gestation. Four developing stages can be divided. Day 13-14; the wall consists of pseudostratified columnar epithelium with a few cells localized in the marginal zone. Yet there is no obvious cytological distinction seen between both. Day 15-16; differentiation of young neurone in the marginal zone. Day 17-19; participation of fiber bundles in the intermediate zone where neurone migrates towards cortical plate. Day 20-22; active differentiation and development of glial cell series start in the subventricular zone and extend throughout wall. The capillary sprouts with mitosis are observed throughout all stages. The endothelial cell and pericyte arise from mesenchymal cord which may be main contributor of mitosis outside of the veretricular and subventricular zones. Polycystic cell of Caley and Maxwell present in the later fetal life and the day of first appearance of this cell are roughly compatible with that of the glioblast. Under pathological conditions the alteration appears to be exaggerated and cells involved increase. Apparent necrotic cellular debris and os m iophilic inclusions of various types can be found within intrinsic neuroectodermal cells in various temporal phase of differentiation and reaction, most abundant in early telencephalic formation and still present occasionally later day of gestation.