The term area 24a refers to one of three parts of area 24o in the anterior cingulate cortex of the human, macaque, rat and mouse. The others in the human and the macaque are area 24b and area 24c. The rat and mouse are similar, except they lack an area 24c ( Vogt-2016 ). In one parcellation of primate cortex, the three areas, a, b, and c, are arrayed in concentric arcs around the genu of the corpus callosum, bordering area 32o externally, and area 33o internally in the human and, in the macaque, abutting the genu directly ( Vogt-2012 ). In a second parcellation, where the focus is to identify equivalent areas in primates and rodents, the subareas are organized from a to b to c, ventral to dorsal ( Vogt-2013 ). In the human and the macaque 24a is bounded ventrally by area s32 and caudally by area 25. In the rat and mouse it is located in the anterior cingulate area ( Swanson-2004; Hof-2000 ) bounded rostrally by area s32 and ventrally by area 25 and the genu of the corpus callosum.