The term area 23 refers to a cytoarchitectural subdivision of the part of cingulate cortex that is located largely in the posterior cingulate gyrus of the limbic lobe. In the human it occupies most of the posterior cingulate gyrus in an arc around the splenium of the corpus callosum, as well as a portion of the adjacent precuneus...caudally, beyond the splenial sulcus. Cytoarchitecturally it is bounded internally by the retrosplenial cortex, which separates it from the splenium of the corpus callosum. It is bounded rostrally by area 24, and caudally by area 31. It is one of two parts of the posterior cingulate cortex, the other being area 31. It has four components: area 23c of Vogt, area 23d of Vogt, and area d23 of the dorsal posterior cingulate cortex, and area v23 of the the ventral posterior cingulate cortex. In the macaque, area 23 is located similarly with regard to the posterior cingulate gyrus and precuneus. Its location relative to other cytoarchitecturally defined areas is also similar to that of the human ( Vogt-2012 ). In the macaque, the internal segmentation into four components differs somewhat from that reported by the authors earlier in their studies ( Vogt-1987; Vogt-1995 ); see area 23 (macaque). Equivalents in the rat and mouse may be present in the cingulate/retrosplenial cortex ( Paxinos-2001 ).