medullary ray (anatomy) medullary ray (anatomy) in anatomy, a medullary ray (ferrein's pyramid) is the middle part of a cortical lobule (or renal lobule). each consists of a group of nephrons in the renal cortex. their name is potentially misleading, as "medullary" refers to their destination, not their location. they travel perpendicular to the capsule, and extend from the cortex to the medulla. they may be visualised during urography. medullary raydetailssystemurinary systemidentifierslatinradii medullaresta98a08.1.01.018ta23378fma74299anatomical terminology additional images medullary rays medullary rays