The term precuneus refers to one of four subdivisions of the parietal lobe identified by dissection in the human ( Carpenter-1983; Ono-1990 ) and the macaque ( Martin-2000 ). Located on the mesial surface of the cerebral hemisphere, it is separated from the postcentral gyrus rostrally by a vertical extension of the cingulate sulcus, the marginal sulcus. Below the cingulate sulcus, it is separated from the posterior cingulate gyrus by the splenial sulcus ( Duvernoy-1992 ). Dorsally it meets the superior parietal lobule at the margin of the hemisphere. Caudally its boundary with the cuneus of the occipital lobe is marked by the parieto-occipital sulcus. Its most caudal and ventral boundaries with the isthmus of the cingulate gyrus and the cuneus are unmarked by anatomical features. The other three parts of the parietal lobe are the postcentral gyrus, the superior parietal lobule, and the inferior parietal lobule. The boundaries in the macaque are the same except that the superior parietal lobule extends onto the mesial surface of the hemisphere where the precuneus is partially separated from it by the cingulate sulcus; and its rostral boundary, largely unmarked by anatomical features, is with the posterior cingulate gyrus ( Martin-2000 ). Equivalent structures are not found in the smooth cerebral cortex of the rat or mouse ( NeuroNames ).