The medulla is made up of 10 to 18 renal pyramids with the base of the pyramids facing the renal cortex and the tips of the pyramids, called renal papilla—or nipples, pointing towards the center of the kidney.
And then we look in a little more detail, you can see the individual papillae come up, and there are little ridges on there, so it's a papilla on papilla and so forth.