Glossary
 Fingers Identified By Roman Numerals
Fingers of a Hand

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Digit
Distal parts of a limb, such as fingers or toes.
These are named and identified by Roman numerals.
In a  pentadactyl (five-fingered or five-toed) arrangement, the most medial digit, if present, is I (e.g. the human thumb) and the most lateral is V (e.g. the human little finger).
Therefore, the human index finger is numbered  II.
In dogs and cats, toe I (the dew claw) is often  vestigial.