Fig 5.

Photomicrographs of fetal cerebrum at (A) 18, (B) 22, (C) 23, and (D) 25 gestational weeks. Images are composite photographs of a transect of the cerebral mantle, and the images have been rescaled for illustration purposes. All original photography is at ×12.5 original magnification, and the superficial aspect of the brain is on the left with the ventricle on the right. At 18 weeks, the intermediate zone has a very cellular superficial region, which is separated from the deeper aspects of the intermediate zone by the developing fiber systems. In contrast, the subplate layer has an abundant extracellular matrix at 18 weeks gestational age, which decreases with increasing gestation. As development progresses, the intermediate zone becomes less cellular, and the deep projecting fiber system becomes thicker such that the cellular superficial region of the intermediate zone becomes harder to distinguish from the subplate layer.