For a further discussion of medieval calendars, as well as the Isabella Breviary itself, please see the post for January.

 

The calendar page for May, from the Breviary of Queen Isabella of Castile, Add MS 18851, f. 3v

This page, from the calendar for May, includes the zodiac sign for Gemini in the upper left of the folio, depicted as a nude man and woman embracing.  A common theme for May miniatures is that of courting and romance, and the lower miniature on this folio is a classic example.  It shows a similar landscape as was depicted in April, with couples walking through a vibrant landscape, and enjoying a ride on a river.