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The original was posted on /r/todayilearned by /u/-Docta-G- on 2025-01-18 16:03:53+00:00.

Original Title: TIL that in utero, a third artery temporarily runs down the arm to help with the development of the hand. By 8 weeks after birth, this artery usually disappears. For unknown reasons, people are retaining this artery as adults, and it’s now three times as prevalent as it was 100 years ago