Vestigial organ

A vestigial organ is a distinct anatomical structure that does not appear to have any function within the human body, but appears consistently and appears to have a function in related species. Their existence is one of the major arguments in favour of evolution.
However, the concept is coming under question as the understanding of physiology improves. For example, the appendix, once thought to be a vestige, is now believed to play an important role in intestinal bacterial flora regulation.
Vestigiality at Wikipedia
Category:Anatomy