This is a slice of the midline vermis in the cerebellum of a 60-day-old rat that was injected with 3H-thymidine on 2 consecutive days: P18 and P19.
The few labeled cells in the MOLECULAR LAYER are judged to be endothelial cells and glia. Unlabeled cells in the GRANULAR LAYER predominate throughout most lobules. There is a scattering of labeled granule cells (most in a superficial location) throughout most lobules. The tuber is the only lobule that has fairly numerous labeled granule cells. By the morning of P18, granule cell neurogenesis is nearly finished.
Most probable composition of the external germinal layer (egl) on P18:
There are a few granule cell precursors in a very thin, discontinuous layer. Most of the proliferating cells are in their final neurogenetic divisions.