Brains of Vespertilionids III. Comparative cytoarchitectonics of the hippocampus

The large size of the hippocampus in the papillose bat (Kerivoula papulosa) (see Part I) is paralleled by a structural differentiation of area CA 1 which is unique among Vespertilionids, and possibly Chiroptera in general. CA 1 of the papillose bat has a very thick band of cells which fills about ²/₃ of the whole thickness of CA 1, in contrast to a maximum of ¹/₃ in other Vespertilionids. As in primates, the cells are dispersed over the whole stratum oriens and reach the alveus. Unlike in primates, however, the cells seem to migrate also in the direction of the periphery, i. e. into the sub-stratum radiatum of the molecular layer. Only a relatively small outer cell-poor band remains (¹/₄ of the whole thickness versus more than ¹/₂ in primates; Table 2). In K. papulosa the cell band of CA 1 is clearly thicker than that of the adjacent neocortex, separated by the lateral ventricle (Fig. 4). So far we have no strong arguments to correlate this very specific structural character with any particular behavior in K. papulosa.