Which preposition to use with cruppers

of Occurrences 15%

On the following morning, he brought around two horses, one of which had a woman's saddle with a velveteen back to it, while on the crupper of the other was a rolled shawl that was to be used for a seat.

behind Occurrences 1%

They repaired to Poitiers; but, four days before Christmas, when the court of Count Alphonso had received all its guests, the Count of La Marche, mounted on his war-horse, with his wife on the crupper behind him, and escorted by his men-at-arms also mounted, cross-bow in hand and in readiness for battle, was seen advancing to the prince's presence.

Which preposition to use with  cruppers