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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: P20 and P21.

Nearly all cells in the GRANULAR LAYER are unlabeled in most lobules; there are a few labeled cells, but these are highly scattered and are usually in a superficial position.  The tuber is the only lobule that has slightly more labeled granule cells.  By the morning of P20, granule cell neurogenesis is virtually complete.

The tuber and pyramis have some dust particles and lint that are artifacts.

 

Most probable composition of the external germinal layer (egl) on P20:

There are a few granule cell precursors in a discontinuous and sparse egl.  All of the proliferating cells are probably in their final neurogenetic divisions.