Vestigial organ
Vestigial organs were parts of one's anatomy that were retained despite an apparent lack or loss of function. The Human appendix was one such example. 

In 2268, Doctor Leonard McCoy noted that the  empath Gem didn't even have any vestigial vocal cords. ()

In 2372, after crossing the warp 10 threshold, Tom Paris's vestigial organs atrophied and dissolved. ()

See also
 Brak'lul
 Redundant organ

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