Human brain, illustration. Surface of the two hemispheres of the human brain. The membranes which cover the brain, the meninges, and the superficial blood vessels have been removed. The largest surface grooves are called fissures and the more numerous and smaller grooves are the sulci. Raised areas of cerebral cortex are called gyri. Lizars, J. 1823 A system of anatomical plates of the human body. W. H.Lizars, Edinburgh.