From the Registrar:
"The size of the law diplomas (14x17) prohibits printing them on sheepskin so law diplomas are printed on a fine white paper."
Oh really? The Size came to the registrar's office and warned that someone would have to sleep with the fishes if the law diplomas were printed on vellum? I find that even less plausible than the excuse that it is simply impossible for our printing service to handle or procure such large sheets of vellum.