The term area 24o refers to the portion of area 24 in anterior cingulate cortex of the human, macaque, rat and mouse. Located in the part of the anterior cingulate gyrus adjacent to the genu of the corpus callosum, it consists of three parts: area 24a, area 24b and area 24c. The rat and mouse lack an area 24c. While original sources name it simply '24' ( Vogt-2012; Ongur-2003 ), it is named '24o' in NeuroNames to eliminate ambiguity with the larger area 24 as defined in Brodmann-1909, i.e., as the combination of all subareas of area 24 including those in both anterior cingulate cortex and midcingulate cortex.