In the response to another question about the names of the fingers in Latin, we learned that the ring finger is often referred to as a digitus medicus or digitus medicinalis: a "medical/medicinal finger."
This seems like a name begging for an explanation. Do we know why the Romans referred to the ring finger in this way?
St Isidore of Seville , who died in 636, said that the ring finger was called the 'digitus medicinalis' because it was used by physicians to apply eye ointment. (Etymologies XI, 1, 70-71) Here is the quotation in Latin: "Quartus [digitus] anularis [vocatus], eo quod in ipso anulus geritur. Idem et medicinalis, quod eo trita collyria a medicis colliguntur." It may have been used to apply other medicines too. Pliny the Elder refers to the use of the ring finger for the application of a concoction of flies to boils - Naturalis Historia, XXX.