<CtrlAltDestroy> Here is my impression of Wikipedia. <CtrlAltDestroy> "There are five fingers on the human hand [citation needed]"
As anyone who's written an essay should be able to tell you, one doesn't need to cite general knowledge (defined as anything that a lay person would be able to find in a general reference work on the subject, without any extra information).
The response to which in the Wikipedia context is "OMG, but we *are* a general reference work, what do we do?" And the response to that is, link to the article on "hand" (or maybe "finger") through the magic of hypertext, and there the person can find all the details they want.
I was assuming that quote was from the article on hand or finger, so a hyperlink wouldn't be very useful.