A Gospel concordance system devised in the fourth century by Eusebius of Caesarea, in which Gospel passages are numbered in the text (generally in the margins) and correspond to tables, arranged in columnar form, indicating the concordance of passages among the Gospels. Canon tables were generally placed at the beginning of the book and were popular in Gospel books, Bibles, and New Testaments (the Gospels plus Acts, Epistles, and Revelation), especially during the early Middle Ages. Canon tables were often set within arched surrounds of an architectural character. Sometimes Evangelist symbols were included to identify the Gospels referred to in the columns of numbers; these are known as beast canon tables.
Michelle Brown. Understanding Illuminated Manuscripts (Malibu, CA: J. Paul Getty Museum in association with the British Library, c1994).