Pages have been trimmed at the edges and parchment strip to join the two half-leaves has been added in restoration. Taken from (1) Decretales Gregorii; (2) Decretum Gratiani; (3) Decretalium Liber Sextus, all from the same Oxford bindery (sample image taken from Decretum Gratiani).
Part of the so-called 'Lost Choirbook II':
GB-Chester, Cheshire and Chester Archives, ZCX/1
GB-London, Royal College of Physicians, MS 734
GB-Nottingham, Archives Office, PR 20,332
GB-Oxford, All Souls College, MS 330
GB-Oxford, New College, printed books Ω.14.5 and C.1.2