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I was reading this Reddit post's comments: 'I am the guy with two penises. AMA' (NSFW), and came upon this discussion (of sorts), where the plural of "penis" has been suggested to be either: "penises", "penii", or "penes".
I looked it up and Wiktionary states that "The hyperforeign Latinate penii is occasionally used as the plural in modern English."
Is "penii" or "penes" also correct in other contexts (medical or scientific, perhaps)? What are the correct plural forms of "penis"?