The term area 15 of Brodmann refers to a subdivision of the cerebral cortex of the guenon defined on the basis of cytoarchitecture. It is located in the part of the insula nearest the limen insula. The cortex is somewhat thinner with less cellular density than in other parts of the insula. The molecular layer of the cerebral cortex (I) is unusually wide; the external granular layer (II) and the external pyramidal layer (III) are less dense, and the internal granular layer (IV) is totally absent, so that the medium-sized pyramidal cells of layer III and the internal pyramidal layer (V) merge with a few isolated granular cells scattered at their boundary. The multiform layer (VI) divides into a more densely cellular outer sublayer (VIa) and a less dense inner sublayer (VIb). As in area 14 of Brodmann (guenon), the sublayer VIb merges with the adjacent claustrum. The cells in all of layer VI form tangential rows similar to the formation seen in area 10 of Brodmann (guenon) and area 11 of Brodmann (guenon) ( Brodmann-1905 ). Area 15 of Brodmann is topologically equivalent to the agranular insula of the macaque. It and area 16 of Brodmann (guenon) together are most nearly equivalent to the agranular insular area of later architectonic segmentations.