In the guenon this area is referred to as area 24 of Brodmann-1905. It includes portions of the cingulate gyrus and the frontal lobe. The cortex is thin; it lacks the internal granular layer (IV) so that the densely distributed, plump pyramidal cells of sublayer 3b of the external pyramidal layer (III) merge with similar cells of the internal pyramidal layer (V); the multiform layer (VI) is very thin (Brodmann-1905). Note that Brodmann later divided this area into two areas, area 24 of Brodmann-1909 and area 25 of Brodmann-1909 (Brodmann-1909).
Subdivisions
The area has been subdivided further, and Vogt et al.[1] distinguish three divisions of the area in the rhesus monkey (Macaca mulatta):
24a: "adjacent to the callosal sulcus"
24b: "has more clearly defined layers II, III, and Va"
24c: "the lower bank of the anterior cingulate sulcus"
