The term area 6b alpha of Vogts refers to a cytoarchitecturally defined subdivision of area 6 of Brodmann (guenon). It and area 6b beta of Vogts constitute area 6b of Vogts. Area 6b alpha differs from area 6a alpha of Vogts in that in 6b alpha the external pyramidal layer (III), while narrower, contains a number of pyramidal cells; a small internal granular layer (IV) is present; the internal pyramidal layer (V) is well differentiated into a cell-rich sublayer (Va) and a cell-poor sublayer (Vb); and the VIa sublayer of the multiform layer (VI) is narrower. Area 6b beta differs from 6b alpha in that the internal granular layer (IV) is wider and more cellular, and in the internal pyramidal layer (V) the cellular sublayer (Va) is narrower while the acellular sublayer (Vb) is wider. Area 6b alpha forms the rostral boundary of area 3a of Vogts. It differs from 3a in that layer III is wider; layer IV is substantially narrower with larger cells; sublayer Va is more densely populated and sublayer Vb less densely populated; and, in layer VI, sublayer VIa has fewer cells and sublayer VIb is wider with a less distinct transition to the subcortical white matter ( Vogts-1919 ).