Which preposition to use with genitals

behind Occurrences 1%

But of all other precedents in this kind, that of Combalus is most memorable; who to prevent his master's suspicion, for he was a beautiful young man, and sent by Seleucus his lord and king, with Stratonice the queen to conduct her into Syria, fearing the worst, gelded himself before he went, and left his genitals behind him in a box sealed up.

in Occurrences 1%

In the Indies there are men who devote themselves to live in the woods and mountains, professing to despise what other men most value, abstaining from every thing but such wild herbs and fruits as are to be found in the woods, and they affix an iron buckle to their genitals in such a manner as to interdict all commerce with woman.

Which preposition to use with  genitals