Why rings are worn on the fourth finger

AN opinion there is, which magnifies the fourth Finger of the left Hand; presuming therein a cordial relation, that a particular vessel, nerve, vein or artery is conferred thereto from the heart, and therefore that especially hath the honour to bear our Rings. Which was not only the Christian practice in Nuptial contracts, but observed by Heathens, as Alexander ab Alexandro, Gellius, Macrobius, and Pierius have delivered, as Levinus Lemnius hath confirmed, who affirms this peculiar vessel to be an artery, and not a Nerve, as Antiquity conceived it; adding moreover that Rings hereon peculiarly affect the Heart; that in Lipothymies or swoundings he used the frication of this Finger with saffron and gold: that the ancient Physitians mixed up their Medicines herewith; that this is seldom or last of all affected with the Gout, and when that becometh nodous, Men continue not long after. Notwithstanding all which we remain unsatisfied, nor can we think the reasons alleadged sufficiently establish the preheminency of this Finger.

For first, Concerning the practice of Antiquity, the custom was not general to weare their Rings either on this Hand or Finger; for it is said, and that emphatically in Jeremiah, Si fuerit Jeconias filius Joachim regis Judæ annulus in manu dextrâ meâ, inde evallam eum; Though Coniah the son of Joachim King of Judah, were the signet on my right Hand, yet would I pluck thee thence. So is it observed by Pliny, that in the portraits of their Gods, the Rings were worn on the Finger next the Thumb; that the Romans wore {them also upon their little Finger, as Nero is described in Petronius; some wore} them on the middle Finger, as the ancient Gaules and Britans; and some upon the fore-Finger, as is deduceable from Julius Pollux: who names that Ring Corionos.

Again, That the practice of the ancients, had any such respect of cordiality or reference unto the Heart, will much be doubted, if we consider their Rings were made of Iron; such was that of Prometheus, who is conceived the first that brought them in use. So, as Pliny affirmeth, for many yeares the Senators of Rome did not wear any Rings of Gold: but the slaves wore generally Iron Rings until their manumission or preferment to some dignity...

And therefore Macrobius discussing the point, hath alleadged another reason; affirming that the gestation of Rings upon this Hand and Finger, might rather be used for their conveniency and preservation, then any cordial relation. For at first (saith he) it was both free and usual to weare Rings on either Hand; but after that luxury encreased, when pretious gems and rich insculptures were added, the custom of wearing them on the right Hand was translated unto the left; for that Hand being lesse imployed, thereby they were best preserved. And for the same reason they placed them on this Finger; for the Thumb was too active a Finger, and is commonly imployed with either of the rest: the Index or fore-Finger was too naked whereto to commit their pretiosities, and hath the tuition of the Thumb scarce unto the second joint: the middle and little Finger they rejected as extreams, and too big or too little for their Rings, and of all chose out the fourth, as being least used of any, as being guarded on either side, and having in most this peculiar condition that it cannot be extended alone and by it self, but will be accompanied by some Finger on either side.

[From Sir Thomas Browne's Pseudodoxia Epidemica (1646), now available fulltext online. The book challenges and refutes many superstitions of the time.] (Via Kottke)