Sulci and Gyri of The Parietal Lobe

Perhaps the most distinguishing feature of the external cerebral surface is its matter made up in a series of convolutions called "gyri" (singular, "gyrum"), between which are grooves of varying depth called "sulci" (singular, "sulcum") or fissures. The parietal lobe is separated from the frontal lobe by the central sulcus, but its boundaries below and behind are somewhat less definite. Below, it is bounded by the posterior ramus of the lateral sulcus and by another arbitrary line drawn from the place where the posterior ramus turns to ascend into the parietal lobe to the point at which this line intersects the back boundary line. Two sulci, the "postcentral sulcus" and the "intraparietal sulcus," subdivide the surface of the parietal lobe into the "postcentral gyrus," the "superior parietal lobule," and the "inferior parietal lobule." The inferior parietal lobule is divided into the "supramarginal gyrus," the "angular gyrus," and an additional posterior convolution. The back boundary of the middle surface of the parietal lobe is formed by the prominent parieto-occipital sulcus, and between these boundaries are located the back portions of both the paracentral lobule and the cingulate gyrus, and the entire "precuneus."