The term area 24a' refers to a part of the posterior midcingulate cortex, which is located caudal to the anterior midcingulate cortex in the anterior cingulate gyrus of the human and the macaque. Located on the ventral margin of the gyrus, it is separated from the corpus callosum by the callosal sulcus. It is defined on the basis of internal structure. In the human it is bounded laterally by area p33' and dorsally by area 24b'. It is subdivided into two parts, area a24a' and area p24a'. In the macaque, which lacks area p33', it is bounded by the corpus callosum in the depth of the callosal sulcus. It exists in the rat and the mouse as well but is not subdivided ( Vogt-2016 ).