![]() In apes and Old World monkeys, the thumb can be rotated around its axis, but the extensive area of contact between the pulps of the thumb and index finger is a human characteristic. The spider monkey compensates for being virtually thumbless by using the hairless part of its long, prehensile tail for grabbing objects. Yet to be classified: other New World monkeys ( tamarins, Aotidae: night or owl monkeys, Pitheciidae: titis, sakis and uakaris, Atelidae: howler and woolly monkeys).Opposable with comparatively long thumbs: gibbons (or lesser apes).Opposable thumbs: Old World monkeys (Circopithecidae) except colobus, and all great apes.Pseudo-opposable thumbs: all strepsirrhines (lemurs, pottos and lorises) and Cebidae (capuchin and squirrel monkeys, which are New World monkeys).Nonopposable thumbs: tarsiers (which are found in the islands of Southeast Asia), marmosets (which are New World monkeys).Primates fall into one of six groups:.Arguably, this definition was chosen to underline what is unique to the human thumb.Ī bonobo "fishing" for termites, an example of incomplete/"untrue" opposition 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. Curls horizontally instead of verticallyĪnd hence the etymology of the word: tum is Proto-Indo-European for 'swelling' (cf 'tumor' and 'thigh') since the thumb is the stoutest of the fingers.Is attached to such a mobile metacarpus (which produces most of the opposability).Has greater breadth in the distal phalanx than in the proximal phalanx.However, recently there have been reports that the thumb, like other fingers, has three phalanges, but lacks a metacarpal bone. The thumb contrasts with each of the other four fingers by being the only one that: Having a dorsal surface that features hair and a nail, and a hairless palmar aspect with fingerprint ridges.Having a skeleton of phalanges, joined by hinge-like joints that provide flexion toward the palm of the hand.The thumb shares the following with each of the other four fingers: 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: The Medical Latin English noun for thumb is pollex (compare hallux for big toe), and the corresponding adjective for thumb is pollical.ĭefinition Thumb and fingers ![]() When a person is standing in the medical anatomical position (where the palm is facing to the front), the thumb is the outermost digit. The thumb is the first digit of the hand, next to the index finger.
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