This is folio 124r from the 9th century illuminated manuscript The Book of Kells (found in Trinity College Library and not visible to Joyce during his lifetime since he went to the Catholic school, University College Dublin), also known as The Book of Columba.  Though this is lovely in color, it is easier to read in black and white.  Note the ourobouros (snake eating itself) hinted by the T of "Tunc" (FW 611.03) and the dragon eating its own border.  "Tunc" has a simple Joycean anagram (cunt), and X marks the spot in the algebraic diagram of ALP's vulva (FW 293):  Colleen Jaurretche usefully compares both images to Courbet's L'Origine du Monde.  The"X" that represents the cross in this page is also the siglum for the Mamalujo (FW 299n4); the broken word strings in the manuscript page ("CRu - CIFIXERANT / LA TRONES") will remind you of the "bi tso fb rok engl"(FW 124.07) in the Mamafesta.  The fact that "eo duos" is given in the illustration as "EDU / OS" is a further hint that any letter can trick the eye:  the D of "duos" is also the O of "eo" (the "O" of the Word and the "D" of the doubled word).  A further wrinkle:  the normal Greek abbreviation for Christ is "XPI" rather than "XRI," and most commentators misread the folio to say this.  All of this lexical confusion reaches its head in I.v:  "plainly inspiring the tenebrous Tunc page of the Book of Kells (and then it need not be lost sight of that there are exactly three squads of candidates for the crucian rose awaiting their turn in the marginal panels of Columkiller [...]" (FW 122.20-23).  The parenthesis after the phrase "Book of Kells" in the Wake is never closed.