Vena amoris is a Latin name meaning, literally, "vein of love".
Traditional belief established that this vein ran directly from the heart to the fourth finger of the left hand. This theory has been cited in western cultures as one of the reasons the engagement ring and/or wedding ring was placed on the fourth finger, or "ring finger". It is to be noted that this traditional belief is a fallacy as all the fingers in the hand have a similar vein structure.
The earliest use of jewellery to signify a bonding was often chains and bracelets. This evolved to the use of the symbolic ring. In ancient Egypt, the Sun and the Moon gods were feared and worshipped. A ring was a symbol of these spirits, both of whom were also related to the home and hearth. The endless circle showed the eternal nature of the bond, while the open centre was meant to be a doorway to things unknown. From wikpedia