Each of the fingers has a name formed from its position, its size or function. So This the strongest is called thumb, index the second, middle the third, fourth ring and pinky the fifth and smaller.
The fourth finger, the ring finger, it was also called in Antiquity "digitus medicinalis, medicus digitus". This deserves an explanation or at least an approximation to an explanation, because it is not an obvious name for itself. What relationship is there between the fourth finger and medicine?
St. Isidore in his Etymologies XI, 1, 70-71 explains these names:
Human beings and their parts
….
The fourth is the ring finger, because it is the one on which the ring is worn. It is also called medical, because physicians use it to apply ointments.
De homine et partibus eius
Quartus anularis, eo quod in ipso anulus geritur. Idem et medicinalis, quod eo trita collyria a medicis colliguntur.
See http://www.antiquitatem.com/en/finfers-the-names-of-fingers-digitus
The fourth is called “anularis”, from “anulus” ("ring") and also honestus and medicus in Latin, because on it the ring is worn, as St. Isidore says.
"anulus" comes from Latin anus, meaning ring, in circular shape. It is clear, then, why it is named so, ano, on Spanish to the "hole in the digestive tract ends and by which the excrement is expelled". (Royal Spanish Academy)
Aulus Gellius offers us a curious, of course unscientific, explanation of why the ancients wore the ring on this finger:
Aulus Gellius, X,11:
The reason why the ancient Greeks and Romans wore a ring on the next to the last finger of the left hand.
I have heard that the ancient Greeks wore a ring on the finger of the left hand which is next to the little finger. They say, too, that the Roman men commonly wore their rings in that way. Apion in his Egyptian History says 2 that the reason for this practice is, that upon cutting into and opening human bodies, a custom in Egypt which the Greeks call ἀνατομαί, or “dissection,” it was found that a very fine nerve proceeded from that finger alone of which we have spoken, and made its way to the human heart; that it therefore seemed quite reasonable that this finger in particular should be honoured with such an ornament, since it seems to be joined, and as it were united, with that supreme organ, the heart. (An English Translation. John C. Rolfe. Cambridge. Cambridge, Mass., Harvard University Press; London, William Heinemann, Ltd. 1927.)
Quae eius rei causa sit, quod et Graeci veteres et Romani anulum hoc digito gestaverint qui est in manu sinistra minimo proximus.
Veteres graecos anulum habuisse in digito accepimus sinistrae manus qui minimo est proximus. Romanos quoque homines aiunt sic plerumque anulis usitatos. Causam esse huius rei Apion in libris Aegyptiacis hanc dicit, quod insectis apertisque humanis corporibus, ut mos in Aegypto fuit, quas Graeci ἀνατομάς appellant, repertum est nervum quendam tenuissimum ab eo uno digito de quo diximus, ad cor hominis pergere ac pervenire; propterea non inscitum visum esse eum potissimum digitum tali honore decorandum, qui continens et quasi conexus esse cum principatu cordis videretur.
Note: Apion who is also referred by Gelius, is who tells us the famous story of Androcles and the Lion in Gellius, 5.14; see http://www.antiquitatem.com/en/androcles-and-the-lion-aulus-gellius
Plutarch also discussed this issue in its Quaestiones convivales 4.8, but we only retain the title of this chapter.
St. Isidore in his Etymologies XIX, 32.2 also refers to this belief so widespread in antiquity but unscientific and false:
The people initially wears rings on the fourth finger from the thumb, because a certain vein runs in it and goes to the heart, and the ancients thought it was necessary to note and adorned them by some special sign.
Anulos homines primum gestare coeperunt quarto a pollice digito, quod eo vena quaedam ad cor usque pertingat, quam notandam ornandamque aliquo insigni veteres putaverunt.
Macrobius repeats and expands the explanation of Aulus Gellius, being the matter of conversation or dialogue of the guests who celebrate the banquet of the feast Saturnalia. At the end of this article you can read the extensive text of Macrobius.
The explanation must look to dialoguer so strange than he leaves ultimately the solution on the hands of everyone.
Macrobius also says that the Egyptians express with this finger the number 6, which is a perfect number.
Why Macrobius called the number 6 a perfect number? A perfect number is a natural number which is equal to the sum of its own positive dividers without considering himself. Thus, 6 is a perfect number because its divisors are 1, 2 and 3; and 6 = 1 + 2 + 3. The following perfect numbers are 28, 496 and 8128.
The Ancients liked greatly to play with these relationships and many more.
Macrobius himself explains it in his commentary on the "Dream of Scipio", Book I, 6, 12
Six, when it joins one makes seven; it is varied and multiple in reverence and power. First, because it is the only one of all numbers below ten numbers which is the result of the sum of its parts. It has a half and a third and sixth, and its half is three, its third is two, its sixth is one and all together make six '
senarius uero qui cum uno coniunctus septenarium facit, uariae ac multiplicis religionis et potentiae est. primum quod solus ex omnibus numeris qui intra decem sunt de suis partibus constat. habet enim medietatem et tertiam partem et sextam partem et est medietas tria, tertia pars duo, sexta pars unum, quae omnia simul sex faciunt.
But the issue of real interest is to find out why they called this finger also "medicinalis" or "doctor's finger" as Macrobius tells us in the quoted passage and also Saint Isidore includes.
Well, "medical finger" is but the translation of the Greek name ring finger ἰατρικός δάκτυλος "iatrikós daktylos". So the fourth finger is called "medical finger" in both Latin and Greek. It is quite possible that the Latin name is a translation from the Greek.
The oldest to the origins of the name reference is in Galen, in his Eisagoge, which reads as follows:
"… This is followed by the next finger to the medium, which is dedicated to physicians (toiv iatroiv anakeimenov) …»
It should be clarified that in antiquity it was widespread the belief in the relationship of the ring finger with the heart or with certain diseases; the physicians of Alexandria extended this theory . They think than nerves or veins come from the heart because of its importance as a center of vitality and creative power; they think the vital force originated in the heart can concentrate on the finger. In some places even the people think in the association of the ring finger of the left hand, the generative power and the principle of motherhood
This may shock us and seem a little odd, but how many are who currently establish a relationship between the dimensions of the fingers and penis size or male member? And is not it striking that some of those who hold this belief seek substantiate it into action that androgens occur on the appendices of various kinds? And what about those who are able to read on a hand the past, present and future of a person?
It is so called because it is the finger that is used to prepare medical potions and applying it to the sick.
Pliny says, for example, in his Naturalis Historia, XXX, (34) 108:
REMEDIES FOR BOILS .
For boils the following remedies are prescribed; a spider, applied before mentioning the insect by name, care being taken to remove it at the end of two days; a shrew-mouse, suspended by the neck till it is dead, care being taken not to let it touch the earth when dead, and to pass it three times around the boil, both operator and patient spitting on the floor each time; poultry-dung, that of a red colour in particular, applied fresh with vinegar; the crop of a stork, boiled in wine; flies, an uneven number of them, rubbed upon the patient with the ring finger; the filth from sheep's ears; stale mutton suet, with ashes of women's hair; ram suet also, with ashes of' burnt pumice and an equal quantity of salt. (The Natural History. Pliny the Elder. John Bostock, M.D., F.R.S. H.T. Riley, Esq., B.A. London. Taylor and Francis, Red Lion Court, Fleet Street. 1855)
Furunculis mederi dicitur araneus, priusquam nominetur, inpositus et tertio die solutus, mus araneus pendens enecatus sic, ut terram ne postea attingat, ter circumlatus furunculo, totiens expuentibus medente et cui is medebitur, ex gallinaceo fimo, quod est rufum, maxime recens inlitum ex aceto, ventriculus ciconiae ex vino decoctus, muscae inpari numero infricatae digito medico, sordes ex pecudum auriculis, sebum ovium vetus cum cinere capilli mulierum, sebum arietis cum cinere pumicis et salis pari pondere.
But the author LászloA. Magyar, in his article Digitus medicinalis. The Etymology of the Name, in Actes du Congrès International d'histoire XXXII of Medicine, Ambres 1990 pat.175-179 offers a certainly interesting explanation. He thinks that the fourth finger, the finger medicinalis, is a finger with magical powers.
The word "medicus, medicinalis" derives from "medeor" Latin verb meaning heal, cure and formerly "heal through magic," as evidenced for example Ernout A. Meillet in his famous Dictionair etymologique de la langue latine, when he defines "medeor"' and reads:
Medical and its derivatives medicus, medicamen (-mentum) often have the sense of "healing through magic" and as the Greek φάρμακον (pharmakon) have taken the meaning of "poisoning", cf. cat. Metzina, poison.
Medico et ses dérivées medicatus, medicamen, (-mentum) ont souvent le sens de “guérir par la magie”, etcomme le gr. φάρμακον (farcamon) ont pris le sens de “empoisonner”, cf.cat. metzina, “poison”
Pharmakon in Greek also means poison and charm, magic.
So the "ring finger" at the time would have been a magic finger, used precisely to heal.
From "medical" come "remedium" and many other derivatives. Moreover this Indo-European root exists in many languages also to mean "think, judge, measure, weigh …"; meditation is the meaning of the Latin verb "Meditor" which is precisely the iterative of "medeor" with this meaning of "thinking" …
So the "medical doctor" who heals with magic, is actually a "medium", mediator who remedies or intermediary between the sick person and the spirits or the powerful forces of divinity or of nature.
Silius Italicus, for example, calls the magicians “Medicum vulgus” in Punica III. 300
Then came the Marmaridae with a sound of clashing arms, a people of magical powers, at whose spell the snake forgot its poison, and at whose touch horned serpents lay still and harmless. (Translated by J.D.Duff).
Note: Cerastae are the Furies, mythological monster with snake hair
Marmaridae, medicum uulgus, strepuere cateruis,
ad quorum cantus serpens oblita ueneni,
ad quorum tactum mites iacuere cerastae.
The German word “Artz” means "medical doctor" but also originally magician; the Greek word “iatros” derives form “iaino”, which has similar connotations .
Moreover, the ring is the most important magical symbol of power, symbol of the relationship between life and death. So the question is whether the fourth finger is magical because it carries the ring or it wears the ring because it is magical; in view of the comments, it seems that wears the ring precisely because it is magical. The full and meaningful name, then, should be "magic finger ring" or "magic ring finger."
Furthermore the theme of medicine and its relationship with magic, religion and temples deserves one or more items. Think on the full votive sanctuaries and places of pilgrimage even today to look body health.
Macrobius, Saturnalia, 7, 13, 6-16
After this, he said, Avienus retrieved from the table the ring that just had fallen from the little finger of the right hand. And when the present asked him why he had preferably placed it on the other hand and finger, not intended for ring wearing, he showed them his left hand, quite swollen because of an wound. From here Horus arose occasion for a question, and says:
Tell me, Disarius, (because everything in the body regards to the knowledge of the physician, and you have reached an understanding even beyond what is demanded by medicine), tell me, I say, why the common assent has convinced everyone that the ring needs to be worn on the finger next to the little finger, which is also called "medical finger" and especially on the left hand?
And Disarius: On this question some conversation had reached me from Egypt, though I doubt whether I should call it a fable or a true story, but when later I consulted anatomists’ books, I discovered the truth: a certain nerve that starts from the heart, runs straight to the finger next to the little finger on the left hand, where it mixes with all the other nerves of that finger. And for that reason it seemed to the ancients that the finger should be surrounded by a ring like a crown.
And Horus said: Indeed it is true that the Egyptians hold that opinion as you say; when I saw in one temple that their priests, called prophets, smeared around each of the images this finger with prepared perfumes and I asked the reason for this, I learned what I said about this nerve because the principal of these priests accounted me and also I learned the number signified by this finger.
Well when this finger is folded indicates the number six, which is in every way full, perfect and divine. He explained in many ways the reasons why this number is full: I now pass over these as less suited to the current conversation. These are the things that I know in Egypt, the country most knowledgeable of all on divine matters, about why the ring is preferably placed on this finger.
In the midst of this discussion Caecina Albinus said: If you're agreeable, I can refer directly what I remember that I have read about this issue in Ateius Capiton, one of the most experts of pontifical law. This determining that it was contrary to divine law to record images of the gods in the rings, reached the point of no silent why the ring is worn on this finger and on this hand.
He said: "The ancients wore with them a ring not as an adornment but to seal. For that reason, it was not allowed to have more than one ring, and only the free person could have it, because only they had the credit that sealing involved. So the slaves did not have the right to wear a ring. On the material of the ring, whether it was iron or gold, a figure was engraved, and each person worn it as each wanted , on either hand and on any finger.
Then he said, in times of luxury, it began the custom of engrave seals on precious gemstones; all this imitation of one another reached to the point that they boasted of increased price they paid for the stones to engrave them. Since then it was avoided the use of the rings on the right hand, which is very busy, and pass it to the left, which is idler, for gemstones would not break with the frequent movement and occupation of the right hand.
He said, on the left hand itself it was chosen the finger next to the pinky as better suited than others to give so precious ring. The thumb, which is so named because that it is strong, is not idle on the left hand nor it is never in less activity than whole hand; that is why, he said, among the Greeks it is called ἀντίχειρ (antikheir, beforehand) like other second hand.
Now, the finger next to the thumb seemed naked and unprotected by its opposite, since the thumb is so smaller that it barely exceeds the base of the other. They avoided the middle finger and the pinky, he said, as inadequate, the one by its magnitude and the other by its smallness; and so it was elected the finger which is enclosed by those two and has less activity and therefore is the best to protected a the ring.
This is what has the pontifical law: let each one pursue, according he wants, the Etruscan opinion or the Egyptian.
His dictis anulum Avienus de mensa rettulit qui illi de brevissimo dexterae manus digito repente deciderat: cumque a praesentibus quaereretur, cur eum alienae manui et digito, et non huic gestamini deputatis potius insereret, ostendit manum laevam ex vulnere tumidiorem. Hinc Horo nata quaestionis occasio, et: Dic, inquit, Disari (omnis enim situs corporis pertinet ad medici notionem, tu vero doctrinam et ultra quam medicina postulat consecutus es), dic, inquam, cur sibi communis adsensus anulum in digito qui minimo vicinus est, quem etiam medicinalem vocant, et manu praecipue sinistra gestandum esse persuasit? Et Disarius: De hac ipsa quaestione sermo quidam ad nos ab Aegypto venerat, de quo dubitabam fabulamne an veram rationem vocarem: sed libris anatomicorum postea consultis verum repperi, nervum quendam de corde natum priorsum pergere usque ad digitum manus sinistrae minimo proximum, et illic desinere inplicatum ceteris eiusdem digiti nervis, et ideo visum veteribus ut ille digitus anula tamquam corona circumdaretur. Et Horus: Adeo, inquit, Disari, verum est ita ut dicis Aegyptios opinari, ut ego sacerdotes eorum, quos prophetas vocant, cum in templo vidissem circa deorum hunc in singulis digitum confectis odoribus inlinere et eius rei causas requisissem, et de nervo quod iam dictum est principe eorum narrante didicerim, et insuper de numero qui per ipsum significatur. 10 Conplicatus enim senarium numerum digitus iste demonstrat, qui omnifariam plenus perfectus atque divinus est. Causasque, cur plenus sit hic numerus, ille multis adseruit: ego nunc ut praesentibus fabulis minus aptas relinquo. Haec sunt quae in Aegypto divinarum omnium disciplinarum compote, cur anulus huic digito magis inferatur, agnovi. Inter haec Caecina Albinus: Si volentibus vobis erit, inquit, in medium profero quae de hac eadem causa apud Ateium Capitonem pontificii iuris inter primos peritum legisse memini: qui cum nefas esse sanciret deorum formas insculpi anulis, eo usque processit ut et cur in hoc digito vel in hac manu gestaretur anulus non taceret. Veteres, inquit, non ornatus sed signandi causa anulum secum circumferebant. Unde nec plus habere quam unum licebat, nec cuiquam nisi libero, quos solos fides deceret quae signaculo continetur: ideo ius anulorum famuli non habebant. Inprimebatur autem sculptura materiae anuli, sive ex ferro sive ex auro foret, et gestabatur, ut quisque vellet, quacumque manu, quolibet digito. Postea, inquit, usus luxuriantis aetatis signaturas pretiosis gemmis coepit insculpere: et certatim haec omnis imitatio lacessivit ut de augmento pretii quo sculpendos lapides parassent gloriarentur. Hinc factum est ut usu anulorum exemptus dexterae, quae multum negotiorum gerit, in laevam relegaretur, quae otiosior est, ne crebru motu et officio manus dexterae pretiosi lapides frangerentur. Electus autem, inquit, in ipsa laeva manu digitus minimo proximus quasi aptior ceteris cui commendaretur anuli pretiositas. Nam pollex, qui nomen ab eo quod pollet accepit, nec in sinistra cessat, nec minus quam tota manus semper in officio est: unde et apud Graecos ἀντίχειρ, inquit, vocatur quasi manus altera. Pollici vero vicinus nudus et sine tuitione alterius adpositi videbatur: nam pollex ita inferior est ut vix radicem eius excedat. Medium et minimum vitaverunt, inquit, ut ineptos, alterum magnitudine, brevitate alterum, et electus est qui ab utroque clauditur et minus officii gerit et ideo servando anulo magis accommodatus est. Haec sunt quae lectio pontificalis habet: unusquisque, ut volet, vel Etruscam vel Aegyptiam opinionem sequatur.