<P> In neuroanatomy, a sulcus (Latin: "furrow", pl . sulci) is a depression or groove in the cerebral cortex . It surrounds a gyrus (pl . gyri), creating the characteristic folded appearance of the brain in humans and other mammals . The larger sulci are usually called fissures . </P> <P> Sulci, the grooves, and gyri, the folds or ridges make up the folded surface of the cerebral cortex . Larger or deeper sulci are termed fissures, and in many cases the two terms are interchangeable . The folded cortex creates a larger surface area for the brain in humans and other mammals . When looking at the human brain, two - thirds of the surface are hidden in the grooves . The sulci and fissures are both grooves in the cortex but they are differentiated by size . A sulcus is a shallower groove that surrounds a gyrus . A fissure is a large furrow that divides the brain into lobes, and also into the two hemispheres as the longitudinal fissure . </P> <P> As the surface area of the brain increases more functions are made possible . A smooth - surfaced brain is only able to grow to a certain extent . A depression, sulcus, in the surface area allows for continued growth . This in turn allows for the functions of the brain to continue growing . </P> <P> The sulcal pattern varies between human individuals, and the most elaborate overview on this variation is probably an atlas by Ono, Kubick and Abernathey: Atlas of the Cerebral Sulci . Some of the more prominent sulci are, however, seen across individuals - and even species - making a common nomenclature across individuals and species possible . </P>

What are the grooves in the brain called