3. A somewhat higher power view of the cortex reveals more of its histological arrangement. Collections of straight tubules form the medullary rays, which run up the center axis of a renal lobule. The border of the renal lobule is defined by the interlobular blood vessels. Between the interlobular blood vessels and the medullary ray are the renal corpuscles and convoluted tubules, together constituting the cortical labyrinth.