The fourth finger (if the thumb counts as the first!) is traditionally the finger on which engagement and wedding rings are worn. But why is this?
It comes from an ancient (and entirely erroneous) belief that a nerve runs from this finger directly to the heart. Given that the heart has always been renowned as the seat of love – hence “giving your heart” and having “heart-felt emotions” – the link to the rings that signified love was appropriate enough.
This idea is also the reason why the finger has been called the “medical finger”. The Greeks and Romans reckoned that the nerve mentioned above would “warn the heart” if the finger came into contact with anything noxious, so the finger was used to stir medical concoctions. Presumably, if your heart jumped a beat during this process you would stop stirring and re-constitute your mixture so that it would be less likely to kill the patient!
Despite the complete lack of evidence for this belief, some people still maintain the superstition that it is unlucky to rub in ointment or scratch the skin with any finger other than the fourth.