Fig. 4: Cytoarchitectonic organization of the anterior MCC of a hemisphere displaying a PCGS in its anterior part and no PCGS in its posterior part.

The MCC of the left hemisphere of CHIMP_2 is presented on a sagittal view of a post-mortem MRI scan. The CGS is marked in red, the PCGS in orange. The Nissl-stained coronal sections presented correspond to the antero-posterior levels defined by a black line on the MRI images (slice 281 where the PCGS is absent, slices 141 and 701 where the PCG is present). On slice 281 where the PCGS is absent, (1) area 24c′ occupies the ventral bank, the fundus, and the lateral-most part of the dorsal bank of the CGS, (2) area 32′ occupies the dorsal bank of the CGS, the gyrus between the CGS and the PCGS and the ventral bank of the PCGS. On slices 141 and 701 where the PCGS is present, (1) area 24c′ occupies the ventral bank, the fundus, and the lateral-most part of the dorsal bank of the CGS, (2) area 32′ occupies the dorsal bank of the CGS, the gyrus between the CGS and the PCGS and the ventral bank of the PCGS. The gray zones identified by a blue arrow correspond to transition zones between two adjacent cytoarchitectonic areas. The photomicrographs of area 32′ (corresponding to the region identified by a blue box on the coronal section of slice #701) and area 24c′ (corresponding to the region identified by a green box on the coronal section of slice #701) are displayed on the right panels. Results show the presence of a dysgranular layer 4 (in red are displayed the granular patches) in area 32′ and the absence of this layer in area 24c′. CGS cingulate sulcus, PCGS paracingulate sulcus, LH left hemisphere, L1-6 cytoarchitectonic layers 1-6, SWM superficial white matter.