Diforc'hioù etre adstummoù "Meud"

10 198 okted lamet ,  11 vloaz zo
Diverradenn ebet eus ar c'hemm
*Un den ''meudek'' a zo amparfal, diampart.
**''Meudeg'', un anv-tiegezh [[brezhonek]].
{{Infobox Anatomy |
Name = The Thumb |
Latin = pollex, digitus primus, digitus I |
GraySubject = |
GrayPage = |
Image = Thumb-up.jpg |
Caption = The "[[Thumbs Up|thumbs up]]" [[gesture]] is a sign of approval in many cultures, but an obscene gesture in many others.<ref>Desmond Morris, Peter Collett, Peter Marsh and Marie O'Shaughnessy, 1979 ''[http://bernd.wechner.info/Hitchhiking/Thumb/ Gestures: Their Origin and Meanings - The Thumb Up]'' Webified by Bernd Wechner</ref> |
Image2 = |
Caption2 = |
Width = 180 |
Precursor = |
System = |
Artery = [[princeps pollicis artery]] |
Vein = |
Nerve = |
Lymph = [[infraclavicular lymph nodes]]<ref>{{NormanAnatomy|clinicalconsiderations}}</ref> |
MeshName = Thumb |
MeshNumber = A01.378.800.667.430.705 |
DorlandsPre = p_27 |
DorlandsSuf = 12655361 |
The '''thumb''' is the [[Human_anatomical_terms#Anatomical_directions|lateral]]-most [[finger|digit]] of the hand. The English adjective for thumb is pollical.
The thumb consists of three bones:
* [[Distal]] [[phalanx bones|phalanx]] (of the first digit)
* [[Proximal]] phalanx (of the first digit)
* First [[metacarpal]]
[[Image:Gray417 color.PNG|thumb|Cross section – forearm]]
[[Image:Gray422.png|thumb|Cross section – hand]]
Its movements are controlled by eight muscles (each with "pollicis" in the name):
{| class="wikitable" class="sortable wikitable"
| '''Name''' || '''Location''' || '''Nerve'''
| [[extensor pollicis longus]] || forearm || [[posterior interosseous nerve]]
| [[abductor pollicis longus]] || forearm || [[posterior interosseous nerve]]
| [[flexor pollicis longus]] || forearm || [[anterior interosseous nerve]]
| [[extensor pollicis brevis]] || forearm || [[posterior interosseous nerve]]
| [[abductor pollicis brevis]] || hand || [[median nerve]]
| [[flexor pollicis brevis]] || hand || [[median nerve]]
| [[opponens pollicis]] || hand || [[median nerve]]
| [[adductor pollicis]] || hand || [[ulnar nerve]] (deep branch)
The extensor pollicis longus tendon and extensor pollicis brevis tendon form what is known as the [[anatomical snuff box]] (an indentation on the lateral aspect of the thumb at its base) The radial artery can be palpated anteriorly at the wrist(not in the snuffbox)
In the hand, the abductor pollicis brevis, adductor pollicis, flexor pollicis brevis, and opponens pollicis form the [[thenar eminence]].
[[Image:Hitchhiker's thumbs.jpg|thumb|Hitchhiker's thumbs]]
===Hitchhiker's thumb===
The thumb when extended (as in a "[[Thumbs Up|thumbs-up]]") can extend backwards toward the nail and outwards, a [[Dominance relationship|recessive]] [[Mendelian inheritance|congenital condition]] known as "hitchhiker's thumb", whereas for other people it will extend straight out with little backward bending. Having either condition appears to have no effect on the thumb's function. While most people have either "hitchhiker's thumb" on both thumbs or neither, in some people, the condition only presents itself on one thumb.
== As one of five digits, and as companion to four fingers ==
The English word "finger" has two senses, even in the context of appendages of a single typical human hand:
# The four digits, not including the thumb.
# Any of the five digits.
Linguistically, it appears that the original sense was the broader of these two: ''penkwe-ros'' (also rendered as ''penqrós'') was, in the inferred [[Proto-Indo-European language|Proto-Indo-European]] language, a suffixed form of ''penkwe'' (or ''penqe''), which has given rise to many [[Indo-European languages|Indo-European]]-family words (tens of them defined in English dictionaries) that involve or flow from concepts of fiveness.
The thumb shares the following with each of the (other) four fingers:
* Having a skeleton of [[phalanges]], joined by hinge-like joints that provide flexion toward the palm of the hand
* Having a "back" surface that features hair and a nail, and a hairless palm-of-the-hand side with [[fingerprint]] ridges instead
The thumb contrasts with each of the (other) four by being the only finger that:
* Is opposable
* Has two phalanges rather than three
* Has its inmost phalanx so close to the wrist
* Has much greater breadth and stubby proportions
* Is attached to such a mobile [[metacarpus]] (which produces most of the opposability)
Typical interdigital grips include the tips of thumb and second finger ([[forefinger]]/[[index finger]]) holding a pill or other small item, or thumb and sides of second and third fingers holding a pen or pencil.
==Origin of the human thumb==
While most primates can oppose their thumb to some of their fingers, the evolution of the fully opposable or [[prehensile]] thumb is usually associated with ''[[Homo habilis]]'', the forerunner of ''[[Homo sapiens]]''.<ref>http://www.reference-wordsmith.com/cgi-bin/lookup.cgi?category=&where=headword&terms=Homo</ref><ref>[http://www.esalenctr.org/display/confpage.cfm?confid=10&pageid=103&pgtype=1 The Evolution of the Human Species (from Evolutionary Theory Conference Summary), Esalen Center for Theory & Research<!-- Bot generated title -->]</ref><ref>[http://www.fortunecity.com/tatooine/acegarp/898/hominids.htm The NEXUS: Technology Timeline - Hominids<!-- Bot generated title -->]</ref> This, however, is the suggested result of evolution from ''[[Homo erectus]]'' (around 1 [[mya (unit)|mya]]) via a series of intermediate [[simian|anthropoid]] stages, and is therefore a much more complicated link.
The most important factors leading to the habile hand (and its thumb) are:
* the freeing of the hands from their walking requirements—still so crucial for [[ape]]s today, as they have hands for feet, which in its turn was one of the consequences of the gradual [[pithecanthropoid]] and anthropoid adoption of the erect [[bipedal]] [[walking]] gait, and
*the simultaneous development of a larger anthropoid [[brain]] in the later stages.
It is possible though that a more likely scenario may be that the specialized, precision gripping hand (equipped with opposable thumb) of ''[[Homo habilis]]'' preceded walking, with the specialized adaptation of the spine, pelvis and lower extremities preceding a more advanced hand. And, it is logical that a conservative, highly functional adaptation be followed by a series of more complex ones that complement it. With ''[[Homo habilis]]'' an advanced grasping-capable hand was accompanied by facultative [[bipedalism]], possibly implying, assuming a co-opted evolutionary relationship exists, that the latter resulted from the former as obligate bipedalism was yet to follow.<ref>W E H Harcourt-Smith and L C Aiello [http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=15198703|Fossils, feet and the evolution of human bipedal locomotion]. J Anat. 2004 May, accessed 2007 November</ref> Walking may have been a byproduct of busy hands and not vice versa.
The thumb, unlike other fingers, is opposable, in that it is the only digit on the human hand which is able to oppose or turn back against the other four fingers, and thus enables the hand to refine its grip to hold objects which it would be unable to do otherwise. The opposable thumb has helped the human species develop more accurate [[fine motor skill]]s. It is also thought to have directly led to the development of tools, not just in humans or their evolutionary ancestors, but other primates as well. The opposable thumb ensured that important human functions such as writing were possible.<ref>http://www.nationalgeographic.com/xpeditions/lessons/01/g68/lonsdorf.html Lesson Plans - Chimps, Humans, Thumbs, and Tools]''[[National Geographic]]'', 2006, accessed April 26, 2007</ref><ref>Damonte, Kathleen [http://www.nsta.org/main/news/stories/science_and_children.php?news_story_ID=49036 Thumbs Are Handy Digits]''[[National Science Teachers Association]]: Science & Children: The Elementary Science Classroom''. February 2004, accessed April 26, 2007</ref> The thumb, in conjunction with the other fingers make humans and other species with similar hands some of the most dexterous in the world.<ref>Chaisson, Eric J. [http://www.tufts.edu/as/wright_center/cosmic_evolution/docs/text/text_bio_6.html Cosmic Evolution - Epoch 6 - Biological Evolution.] ''[[Tufts University]]''. 2007, accessed April 26, 2007</ref>
==Other animals with opposable thumbs==
Many animals also have some kind of opposable thumb or toe.
[[Image:Oppossumthumb.jpg|thumb|right|opposable thumb on rear foot of an opossum]]
* Most [[primate]]s
**[[Ape]]s, including the [[great ape]]s ([[Bonobo]], [[Chimpanzee]], [[Gorilla]], [[Orangutan]]) and the [[gibbon]]s—opposable thumbs on both hands and feet.
** [[Old World Monkeys]], with some exceptions, such as the genera ''[[Piliocolobus]]'' and ''[[Colobus]]''.
** Some [[Cebid]]s ([[New World monkey|New World primates]] of Central and South America).
**Many [[strepsirrhine]] primates, such as [[lemur]]s, [[loris]]es, and the [[Aye-aye]].
* [[Giant Panda]]s - five clawed fingers plus an extra-long [[sesamoid bone]] that, though not really a finger (as the human thumb is), works like an opposable thumb.
* Most [[phalangerid]] [[marsupial]]s (a family of [[possum]]s) - an opposable [[toe]] on each foot, plus two opposable digits on each hand
* [[Koala]]s - similar to phalangerids, though they are in a different order.
* [[Opossum]]s - opposable "thumbs" on the rear feet.
* ''[[Troodon]]'', a birdlike dinosaur - partially opposable thumbs.
* ''[[Bambiraptor]]'', a small, predatory dinosaur - it could touch the outer two of its three digits together in an opposable grip.
* ''[[Phyllomedusa]]'', a genus of frogs native to South America.
Most [[bird]]s have at least one opposable digit on the foot, in [[Dactyly#In_birds|various configurations]], but these are seldom called "thumbs".
{{human anatomical features}}
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