gyrus, gen. and pi. gy'ri

(ji'rus) [G. gyros, circle.] Convolution, one of the prominent rounded elevations on the surface of the hemispheres of the brain; they are separated from each other by more or le deep furrows, the fi ures or sulci. convolution in the inferior parietal lobule formed by the united ends of the superior and middle temporal gyri bending round the posterior upturned extremity of the superior temporal sulcus. g. transitivus [BNA]. radiating gyri converging toward the insular pole, making up the pre insula. volution, ascending frontal convolution, the posterior convolution of the frontal lobe bounded posteriorly by the fi ure of Rolando and anteriorly by the pre central sulcus. volution, ascending parietal convolution, the anterior convolution of the parietal lobe, bounded in front by the fi ure of Rolando and posteriorly by the interparietal sulcus. callosal convolution, g. fomicatus (of the older nomenclature), a long, curved convolution arching over the corpus callosum, from which it is separated by the sulcus corp or is callosi; on its upper surface it is bounded by the sulcus cinguli and (posteriorly) by the sulcus sub parietal is; it forms the upper part of the limbic lobe, or g. fomicatus [BNA]. campi [BNA]. lobe, falciform lobe, a long, ring-like convolution on the mesial aspect of the hemisphere, encircling the corpus callosum; its various parts are called g. cinguli, isthmus, g. hippocampi, and uncus. (The [BNA] term for gyrus fomicatus of the older nomenclature is gyrus cinguli.) tion, g. central is anterior [BNA]. tion, a broad convolution on the outer surface of the frontal lobe of the cerebrum between the inferior frontal sulcus and the fi ure of Sylvius; it is divided by branches of the Sylvian fi ure into three parts: pars basilar is (opercular is [BNA]), pars triangular is, and pars orbital is; the first two constitute a portion of the operculum. tion, a convolution on the convex surface of each frontal lobe of the cerebrum running in an anteroposterior direction between the superior and inferior frontal sulci; it is divided into an upper and a lower portion by the middle frontal sulcus.