Primatologists and hand research pioneers John and Prudence Napier defined opposition as: "A movement by which the pulp surface of the thumb is placed squarely in contact with – or diametrically opposite to – the terminal pads of one or all of the remaining fingers." For this true, pulp-to-pulp opposition to be possible, the thumb must rotate about its long axis (at the carpometacarpal joint). Moving a limb back to its neutral position is called reposition and a rotary movement is referred to as circumduction. Other researchers use another definition, referring to opposition-apposition as the transition between flexion-abduction and extension-adduction the side of the distal thumb phalanx thus approximated to the palm or the hand's radial side (side of index finger) during apposition and the pulp or "palmar" side of the distal thumb phalanx approximated to either the palm or other fingers during opposition.
To anatomists, this makes sense as two intrinsic hand muscles are named for this specific movement (the opponens pollicis and opponens digiti minimi respectively). Some anatomists restrict opposition to when the thumb is approximated to the fifth finger (little finger) and refer to other approximations between the thumb and other fingers as apposition. Opposition and apposition Humans Īnatomists and other researchers focused on human anatomy have hundreds of definitions of opposition.
Linguistically, it appears that the original sense was the first of these two: penkwe-ros (also rendered as penqrós) was, in the inferred Proto-Indo-European language, a suffixed form of penkwe (or penqe), which has given rise to many Indo-European-family words (tens of them defined in English dictionaries) that involve, or stem from, concepts of fiveness. Any of the four terminal members of the hand, other than the thumb.Any of the five terminal members of the hand.The English word finger has two senses, even in the context of appendages of a single typical human hand:
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