Francis Crick, one of the discoverers of DNA, listed area 24 as the seat of free will because of its centrality in abulia and amotivational syndromes.
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).
The area has been subdivided further, and Vogt et al. make three division for the area in the rhesus monkey (Macaca mulatto):
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"
External links and references
^ Brent A. Vogt, Deepak N. Pandya, Douglas L. Rosene, "Cingulate cortex of the rhesus monkey: I. Cytoarchitecture and thalamic afferents," The Journal of Comparative Neurology, 262(2):256-270, 1987.
For a list of Brodmann areas visit http://spot.colorado.edu/~dubin/talks/brodmann/neuronames.html