Have you ever wondered...?
The ancient Romans believed the vein in the fourth or “ring” ringer of the left hand was the most direct path to the heart. This vein – called the “vena amoris” – is known as the vein of love. In early Christian ceremonies, the groom would take the ring and touch his bride’s thumb (“In the name of the Father”), then the index finger (“and the Son”), the middle finger (“and the Holy Ghost”), then “Amen” as he placed the ring on the fourth finger, which sealed the marriage. Another interesting fact is in many Jewish ceremonies, the wedding ring is placed on the index finger (believed to be the closest way to the heart), and is moved to the ring finger depending on the custom of where the bride lives.
*excerpt found here.