De officiis ministrorum ("On the Offices of Ministers" or, "On the Duties of the Clergy"), Book I, ch. 48. http://books.google.com/books?id=ZIwXAAAAIAAJ&pg=PA114&dq=%22ante+agnus+offerebatur%22&hl=en&ei=pTDSTcflDsrZ0QHjxKHYCw&sa=X&oi=book_result&ct=result&resnum=4&ved=0CDgQ6AEwAzgy#v=onepage&q=%22ante%20agnus%20offerebatur%22&f=false
In, The Eucharist in the West: History and Theology, Edward J. Kilmartin, SJ, Robert J. Daly, SJ, Editor, 1998, The Liturgical Press, ISBN 0814662048 ISBN 9780814662045, p. 19 http://books.google.com/books?id=WI2gC7lFmC4C&pg=PA19&lpg=PA19&dq=%22Christ+is+offered+today%22&source=bl&ots=MoKJXo6d2u&sig=8k0xytaJpidX3wg5RpQQKHwDxzw&hl=en&ei=hi_STbuzOYq_0AHwxKXKCw&sa=X&oi=book_result&ct=result&resnum=2&ved=0CBwQ6AEwAQ#v=onepage&q=%22Christ%20is%20offered%20today%22&f=false
Alternate translation: In old times a lamb, a Calf was offered; now Christ is offered. But He is offered as man and as enduring suffering. And He offers Himself as a priest to take away our sins, here in an image, there in truth, where with the Father He intercedes for us as our Advocate. http://www.newadvent.org/fathers/34011.htm