It appears that the early Hebrews placed the wedding ring on the index finger and in India, nuptial rings were worn on the thumb. The Western custom of placing a wedding ring on the “third” finger (not counting the thumb) began with the Greeks, through carelessness in cataloguing human anatomy. Greek physicians in the third century B.C. believed that a certain vein, the “vein of love,” ran from the “third finger” directly to the heart. It became the logical digit to carry a ring symbolising an affair of the heart. The Romans, plagiarising Greek anatomy charts, adopted the ring practice unquestioningly. They did attempt to clear up the ambiguity surrounding exactly what finger constituted the third, introducing the phrase “the finger next to the least.”
This also became the Roman physician’s “healing finger,” used to stir mixtures of drugs. Since the finger’s vein supposedly ran to the heart, any potentially toxic concoction would be readily recognised by a doctor “in his heart” before being administered to a patient. The Christians continued this ring-finger practice, but worked their way across the hand to the vein of love. A groom first placed the ring on the top of the bride’s index finger, with the words “In the name of the Father.” Then, praying, “In the name of the Son,” he moved the ring to her middle finger, and finally, with the concluding words “and of the Holy Spirit, Amen,” to the third finger. This was known as the Trinitarian formula.
In the East,however, they did not approve of finger rings, believing them to be merely ornamental, lacking social symbolism or religious significance.