Leaf from a Volume of Johannes Andrea's "Lectura super arboris consanguinitatis et affinitatis: Table of Affinity, c. 1331. The two leaves shown here come from Iohannes Andrea's widely circulated treatise on marriage impediments. The writer lived until 1348 and is known as the most learned of the lay canonists of the Middle Ages. He taught for nearly fifty years at the University of Bologna, where his lectures on both canon and Roman law made him famous.