Structural organization of 'callosal' OBg in human corpus callosum agenesis.

The structural organization of the 'callosal' OBg was studied in Nissl and Weil stained sections of two human brains completely lacking in the corpus callosum. OBg of the normal brain contains a set of distinctive large pyramidal cells in layer III. By contrast, in the brains with absence of the corpus callosum, layer III of OBg contained a slightly reduced number of smaller pyramidal cells than normal, and the characteristic large pyramidal cells were scarsely detectable. Other layers of OBg were not definitely changed. Furthermore, 'acallosal' striate cortex revealed no specific changes. From these observations, it was suggested that the large layer III pyramids of OBg might be closely related to callosal connections.