I might well be perpetuating an urban legend.

Edit: seems that there is some theory advanced by real biblical scholars, but it also seems that it is highly unlikely to be true:

https://www.haaretz.com/jewish/god-didn-t-use-adam-s-penis-b...

Image search for הצלע pretty much gives rib (and rib cuts). On the other hand, it's unclear that all of the many biblical references to feet are meant literally as pedal extremities.