Yo, medieval scribes: no one's going to read the text you so painstakingly lettered if you continue to draw weird and dirty pictures in the margins. Well, I guess you're all dead, so we can't fix this now, can we?
A penis tree
From a 14th century copy of Romance of the Rose.
A monkey with an arrow stuck in its butt
From Bibliothèque Mazarine MS 520.
Ass arrows, again
From the Rutland Psalter, c. 1260.
An inappropriate rabbit
From Breviary, Use of Verdun c. 1302-1305.