蟻の門渡り

• IPA^(key): [a̠ɾʲi no̞ to̞ β̞a̠ta̠ɾʲi]

蟻(あり)の門(と)渡(わた)り • (ari no to watari) 

1. perineum

   Synonyms: 会陰 (ein), 会陰部 (einbu)

2. a narrow pass, a precipice
3. Used other than figuratively or idiomatically: see 蟻,‎ 門,‎ 渡る.

Literally “ants’ passage”, the phrase appears in nature poetry from the 12th century referring to lines of ants walking on the ground. The popular sense “perineum” alludes to an 18th century work by Hiraga Gennai about lice crossing the “valley of the underwear” (褌(ふんどし)谷(たに) (fundoshi-tani)).^[1]