The term agranular cortex is a cytoarchitecturally defined term denoting the type of heterotypic cortex that is distinguished by its relative thickness and lack of granule cells in both the external granular layer and the internal granular layer. For illustrations click 'Internal Structure' for area 4 of Brodmann (guenon) and area 6 of Brodmann (guenon). The agranular cortex of the frontal lobe is topologically equivalent to motor cortex in the human ( Brodmann-1909 ), the macaque ( Wise-1985a ), the rat ( Swanson-2004 ) and the mouse ( Hof-2000 ).