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The renal medulla (pyramid) is composed of conical masses of tissue called renal pyramids, whose bases are directed toward the convex surface of the kidney, and which apex to form the renal papillae. The renal cortex forms a shell around the medulla. Its tissues dip into the medulla between adjacent renal pyramids to form renal columns. The granular appearance of the cortex is due to the random arrangementmycontentbreak of tiny tubules associated with nephrons, the functional units of the kidney.