LEVEL 4 is a more lateral slice of the dorsal hippocampus in the same P20 rat.   Compare the size differences between the P10 rat, this rat, and the P40 rat.

Much like Level 3, the granular layer is filled with labeled cells that stack up beneath the older, unlabeled cells.  Differences between the external and internal limb are difficult to distinguish.  Both limbs have a thin superficial layer of prenatally generated granule cells.