Pigment architecture of the human telencephalic cortex. V. Regio anterogenualis.

Cortical lamination and parcellation of the anterogenual region in the human brain is studied in sections successively stained for nerve cells (15 micrometers), myelin sheaths (100 micrometers), and lipofuscin granules (800 micrometers). The anterogenual region covers a crescent-shaped territory in front of the genu corporis callosi. It abuts on the allocortex, i.e., the supracallosal derivatives of the cornu ammonis and subiculum on the one side, and the mature frontal isocortex on the other side. The region is divisible into four areas. The transitory unitoteniate area ectogenualis is followed by anterogenual core fields, which show an outstandingly internopyramidal and internoteniate character. Furthermore, the core is of the infraradiate type and shows only the lower band of Baillarger. It is magnocellular, generally poor in myelinated fibres (typus pauper) and rich in pigment (typus obscurus). Minor structural differences permit the distinction of the area anterogenualis simplex from the area anterogenualis magnoganglionaris. Especially in the magnoganglionic field, layer Vb is richly endowed with a large, particularly slender and pigment-laden type of pyramidal cell. Within the proisocortex this special constituent occurs only in the anterogenual region. Structural features indicate its relationship to the Betz-pyramids of the cingulate and precentral ganglionic core fields. The transitory area paragenualis can be considered a belt-area accompanying the anterogenual core. It is weakly internopyramidal and internoteniate, thereby mediating to the surrounding frontal isocortex.