Ring finger

In the days before the circulatory system was fully understood, it was a common belief that a vein ran directly from the fourth finger of the left hand to the heart.  They called it the vena amoris - the vein of love.  It was this belief that led to the custom of wearing wedding rings - and later engagement rings - on this finger.  At first only women wore wedding rings.  The custom did not really extend to men until well into the beginning of the 20th century - perhaps as a result of so many couples being separated by war.