[Jump to content](#bodyContent) Main menu Main menu move to sidebar hide Navigation - [Main page](/wiki/Main_Page "Visit the main page [z]") - [Contents](/wiki/Wikipedia:Contents "Guides to browsing Wikipedia") - [Current events](/wiki/Portal:Current_events "Articles related to current events") - [Random article](/wiki/Special:Random "Visit a randomly selected article [x]") - [About Wikipedia](/wiki/Wikipedia:About "Learn about Wikipedia and how it works") - [Contact us](//en.wikipedia.org/wiki/Wikipedia:Contact_us "How to contact Wikipedia") Contribute - [Help](/wiki/Help:Contents "Guidance on how to use and edit Wikipedia") - [Learn to edit](/wiki/Help:Introduction "Learn how to edit Wikipedia") - [Community portal](/wiki/Wikipedia:Community_portal "The hub for editors") - [Recent changes](/wiki/Special:RecentChanges "A list of recent changes to Wikipedia [r]") - [Upload file](/wiki/Wikipedia:File_upload_wizard "Add images or other media for use on Wikipedia") - [Special pages](/wiki/Special:SpecialPages) [![](/static/images/icons/wikipedia.png) ![Wikipedia](/static/images/mobile/copyright/wikipedia-wordmark-en.svg) ![The Free Encyclopedia](/static/images/mobile/copyright/wikipedia-tagline-en.svg) ](/wiki/Main_Page) [ Search](/wiki/Special:Search "Search Wikipedia [f]") Search Appearance - [Donate](https://donate.wikimedia.org/?wmf_source=donate&wmf_medium=sidebar&wmf_campaign=en.wikipedia.org&uselang=en) - [Create account](/w/index.php?title=Special:CreateAccount&returnto=Thumb "You are encouraged to create an account and log in; however, it is not mandatory") - [Log in](/w/index.php?title=Special:UserLogin&returnto=Thumb "You're encouraged to log in; however, it's not mandatory. [o]") Personal tools - [Donate](https://donate.wikimedia.org/?wmf_source=donate&wmf_medium=sidebar&wmf_campaign=en.wikipedia.org&uselang=en) - [ Create account](/w/index.php?title=Special:CreateAccount&returnto=Thumb "You are encouraged to create an account and log in; however, it is not mandatory") - [ Log in](/w/index.php?title=Special:UserLogin&returnto=Thumb "You're encouraged to log in; however, it's not mandatory. [o]") Pages for logged out editors [learn more](/wiki/Help:Introduction) - [Contributions](/wiki/Special:MyContributions "A list of edits made from this IP address [y]") - [Talk](/wiki/Special:MyTalk "Discussion about edits from this IP address [n]") ## Contents move to sidebar hide - [](#) (Top) - [](#Definition) 1 Definition Toggle Definition subsection - [](#Thumb_and_fingers) 1.1 Thumb and fingers - [](#Opposition_and_apposition) 2 Opposition and apposition Toggle Opposition and apposition subsection - [](#Humans) 2.1 Humans - [](#Other_primates) 2.2 Other primates - [](#Other_placental_mammals) 2.3 Other placental mammals - [](#Marsupials) 2.4 Marsupials - [](#Reptiles) 2.5 Reptiles - [](#Dinosaurs) 2.6 Dinosaurs - [](#Birds) 2.6.1 Birds - [](#Pterosaurs) 2.6.2 Pterosaurs - [](#Amphibians) 2.7 Amphibians - [](#Human_anatomy) 3 Human anatomy Toggle Human anatomy subsection - [](#Skeleton) 3.1 Skeleton - [](#Muscles) 3.2 Muscles - [](#Extrinsic) 3.2.1 Extrinsic - [](#Intrinsic) 3.2.2 Intrinsic - [](#Variations) 3.3 Variations - [](#Grips) 3.4 Grips - [](#Human_evolution) 4 Human evolution - [](#See_also) 5 See also - [](#Notes) 6 Notes - [](#References) 7 References - [](#External_links) 8 External links Toggle the table of contents # Thumb 103 languages - [अंगिका](https://anp.wikipedia.org/wiki/%E0%A4%85%E0%A4%82%E0%A4%97%E0%A5%82%E0%A4%A0%E0%A4%BE "अंगूठा – Angika") - [Ænglisc](https://ang.wikipedia.org/wiki/%C3%9E%C5%ABma "Þūma – Old English") - [العربية](https://ar.wikipedia.org/wiki/%D8%A5%D8%A8%D9%87%D8%A7%D9%85 "إبهام – Arabic") - [Aragonés](https://an.wikipedia.org/wiki/Pulgar "Pulgar – Aragonese") - [ܐܪܡܝܐ](https://arc.wikipedia.org/wiki/%DC%9F%DC%AA%DC%AC%DC%90 "ܟܪܬܐ – Aramaic") - [अवधी](https://awa.wikipedia.org/wiki/%E0%A4%85%E0%A4%99%E0%A5%81%E0%A4%A0%E0%A4%BE "अङुठा – Awadhi") - [Azərbaycanca](https://az.wikipedia.org/wiki/Ba%C5%9F_barmaq "Baş barmaq – Azerbaijani") - [Basa Bali](https://ban.wikipedia.org/wiki/Inan_lima "Inan lima – Balinese") - [বাংলা](https://bn.wikipedia.org/wiki/%E0%A6%AC%E0%A7%83%E0%A6%A6%E0%A7%8D%E0%A6%A7%E0%A6%BE%E0%A6%99%E0%A7%8D%E0%A6%97%E0%A7%81%E0%A6%B2%E0%A6%BF "বৃদ্ধাঙ্গুলি – Bangla") - [閩南語 / Bân-lâm-gú](https://zh-min-nan.wikipedia.org/wiki/T%C5%8Da-th%C3%A2u-b%C3%BA "Tōa-thâu-bú – Minnan") - [Bikol Central](https://bcl.wikipedia.org/wiki/Tangan "Tangan – Central Bikol") - [Български](https://bg.wikipedia.org/wiki/%D0%9F%D0%B0%D0%BB%D0%B5%D1%86 "Палец – Bulgarian") - [Boarisch](https://bar.wikipedia.org/wiki/Daam "Daam – Bavarian") - [Bosanski](https://bs.wikipedia.org/wiki/Palac "Palac – Bosnian") - [Brezhoneg](https://br.wikipedia.org/wiki/Meud "Meud – Breton") - [Català](https://ca.wikipedia.org/wiki/Polze "Polze – Catalan") - [Чӑвашла](https://cv.wikipedia.org/wiki/%D0%9F%D0%B0%D1%88-%D0%BF%D3%B3%D1%80%D0%BD%D0%B5 "Паш-пӳрне – Chuvash") - [Čeština](https://cs.wikipedia.org/wiki/Palec "Palec – Czech") - [Dansk](https://da.wikipedia.org/wiki/Tommelfinger "Tommelfinger – Danish") - [Deitsch](https://pdc.wikipedia.org/wiki/Daume "Daume – Pennsylvania German") - [Deutsch](https://de.wikipedia.org/wiki/Daumen "Daumen – German") - [ދިވެހިބަސް](https://dv.wikipedia.org/wiki/%DE%84%DE%AE%DE%91%DE%AA%DE%88%DE%A6%DE%87%DE%A8_%DE%87%DE%A8%DE%82%DE%8E%DE%A8%DE%8D%DE%A8 "ބޮޑުވައި އިނގިލި – Divehi") - [Eesti](https://et.wikipedia.org/wiki/P%C3%B6ial "Pöial – Estonian") - [Ελληνικά](https://el.wikipedia.org/wiki/%CE%91%CE%BD%CF%84%CE%AF%CF%87%CE%B5%CE%B9%CF%81%CE%B1%CF%82 "Αντίχειρας – Greek") - [Эрзянь](https://myv.wikipedia.org/wiki/%D0%9F%D0%B5%D0%BB%D1%8C%D0%BA%D0%B0 "Пелька – Erzya") - [Español](https://es.wikipedia.org/wiki/Dedo_pulgar "Dedo pulgar – Spanish") - [Esperanto](https://eo.wikipedia.org/wiki/Dikfingro "Dikfingro – Esperanto") - [Euskara](https://eu.wikipedia.org/wiki/Erpuru "Erpuru – Basque") - [فارسی](https://fa.wikipedia.org/wiki/%D8%B4%D8%B3%D8%AA "شست – Persian") - [Français](https://fr.wikipedia.org/wiki/Pouce_(anatomie) "Pouce (anatomie) – French") - [Frysk](https://fy.wikipedia.org/wiki/Tomme "Tomme – Western Frisian") - [Gaeilge](https://ga.wikipedia.org/wiki/Ord%C3%B3g "Ordóg – Irish") - [Gàidhlig](https://gd.wikipedia.org/wiki/%C3%92rdag "Òrdag – Scottish Gaelic") - [Galego](https://gl.wikipedia.org/wiki/Polgar "Polgar – Galician") - [ગુજરાતી](https://gu.wikipedia.org/wiki/%E0%AA%85%E0%AA%82%E0%AA%97%E0%AB%82%E0%AA%A0%E0%AB%8B "અંગૂઠો – Gujarati") - [한국어](https://ko.wikipedia.org/wiki/%EC%97%84%EC%A7%80%EC%86%90%EA%B0%80%EB%9D%BD "엄지손가락 – Korean") - [Հայերեն](https://hy.wikipedia.org/wiki/%D4%B2%D5%B8%D6%82%D5%A9_%D5%B4%D5%A1%D5%BF "Բութ մատ – Armenian") - [हिन्दी](https://hi.wikipedia.org/wiki/%E0%A4%85%E0%A4%82%E0%A4%97%E0%A5%81%E0%A4%B7%E0%A5%8D%E0%A4%A0 "अंगुष्ठ – Hindi") - [Hrvatski](https://hr.wikipedia.org/wiki/Palac "Palac – Croatian") - [Ido](https://io.wikipedia.org/wiki/Polexo "Polexo – Ido") - [Bahasa Indonesia](https://id.wikipedia.org/wiki/Ibu_jari "Ibu jari – Indonesian") - [Italiano](https://it.wikipedia.org/wiki/Pollice_(dito) "Pollice (dito) – Italian") - [עברית](https://he.wikipedia.org/wiki/%D7%90%D7%92%D7%95%D7%93%D7%9C "אגודל – Hebrew") - [Jawa](https://jv.wikipedia.org/wiki/Jempol "Jempol – Javanese") - [ಕನ್ನಡ](https://kn.wikipedia.org/wiki/%E0%B2%B9%E0%B3%86%E0%B2%AC%E0%B3%8D%E0%B2%AC%E0%B3%86%E0%B2%B0%E0%B2%B3%E0%B3%81 "ಹೆಬ್ಬೆರಳು – Kannada") - [Қазақша](https://kk.wikipedia.org/wiki/%D0%91%D0%B0%D1%80%D0%BC%D0%B0%D2%9B "Бармақ – Kazakh") - [Kiswahili](https://sw.wikipedia.org/wiki/Kidole_gumba "Kidole gumba – Swahili") - [Kreyòl ayisyen](https://ht.wikipedia.org/wiki/Pous_(anatomi) "Pous (anatomi) – Haitian Creole") - [Latina](https://la.wikipedia.org/wiki/Pollex_(anatomia) "Pollex (anatomia) – Latin") - [Latviešu](https://lv.wikipedia.org/wiki/%C4%AAk%C5%A1%C4%B7is "Īkšķis – Latvian") - [Ligure](https://lij.wikipedia.org/wiki/P%C5%93uxo_(dio) "Pœuxo (dio) – Ligurian") - [Lombard](https://lmo.wikipedia.org/wiki/Mazza-pioeugg "Mazza-pioeugg – Lombard") - [Македонски](https://mk.wikipedia.org/wiki/%D0%9F%D0%B0%D0%BB%D0%B5%D1%86 "Палец – Macedonian") - [मराठी](https://mr.wikipedia.org/wiki/%E0%A4%85%E0%A4%82%E0%A4%97%E0%A4%A0%E0%A4%BE "अंगठा – Marathi") - [Bahasa Melayu](https://ms.wikipedia.org/wiki/Ibu_jari "Ibu jari – Malay") - [閩東語 / Mìng-dĕ̤ng-ngṳ̄](https://cdo.wikipedia.org/wiki/Du%C3%A2i-c%C4%81i "Duâi-cāi – Mindong") - [မြန်မာဘာသာ](https://my.wikipedia.org/wiki/%E1%80%9C%E1%80%80%E1%80%BA%E1%80%99_(%E1%80%81%E1%80%94%E1%80%B9%E1%80%93%E1%80%AC%E1%80%97%E1%80%B1%E1%80%92) "လက်မ (ခန္ဓာဗေဒ) – Burmese") - [Nederlands](https://nl.wikipedia.org/wiki/Duim_(vinger) "Duim (vinger) – Dutch") - [नेपाली](https://ne.wikipedia.org/wiki/%E0%A4%AC%E0%A5%82%E0%A4%A2%E0%A5%80_%E0%A4%94%E0%A4%81%E0%A4%B2%E0%A4%BE "बूढी औँला – Nepali") - [日本語](https://ja.wikipedia.org/wiki/%E8%A6%AA%E6%8C%87 "親指 – Japanese") - [Norsk bokmål](https://no.wikipedia.org/wiki/Tommel "Tommel – Norwegian Bokmål") - [Norsk nynorsk](https://nn.wikipedia.org/wiki/Tommelfinger "Tommelfinger – Norwegian Nynorsk") - [Occitan](https://oc.wikipedia.org/wiki/Poce "Poce – Occitan") - [ਪੰਜਾਬੀ](https://pa.wikipedia.org/wiki/%E0%A8%85%E0%A9%B0%E0%A8%97%E0%A9%82%E0%A8%A0%E0%A8%BE "ਅੰਗੂਠਾ – Punjabi") - [Pangasinan](https://pag.wikipedia.org/wiki/Tangan "Tangan – Pangasinan") - [پنجابی](https://pnb.wikipedia.org/wiki/%D8%A7%D9%86%DA%AF%D9%88%D9%B9%DA%BE%D8%A7 "انگوٹھا – Western Punjabi") - [Plattdüütsch](https://nds.wikipedia.org/wiki/Dumen "Dumen – Low German") - [Polski](https://pl.wikipedia.org/wiki/Kciuk "Kciuk – Polish") - [Português](https://pt.wikipedia.org/wiki/Polegar "Polegar – Portuguese") - [Ripoarisch](https://ksh.wikipedia.org/wiki/Dumm "Dumm – Colognian") - [Română](https://ro.wikipedia.org/wiki/Deget_mare "Deget mare – Romanian") - [Русский](https://ru.wikipedia.org/wiki/%D0%91%D0%BE%D0%BB%D1%8C%D1%88%D0%BE%D0%B9_%D0%BF%D0%B0%D0%BB%D0%B5%D1%86 "Большой палец – Russian") - [संस्कृतम्](https://sa.wikipedia.org/wiki/%E0%A4%85%E0%A4%99%E0%A5%8D%E0%A4%97%E0%A5%81%E0%A4%B7%E0%A5%8D%E0%A4%A0%E0%A4%83 "अङ्गुष्ठः – Sanskrit") - [ᱥᱟᱱᱛᱟᱲᱤ](https://sat.wikipedia.org/wiki/%E1%B1%A6%E1%B1%9F%E1%B1%B2%E1%B1%9F%E1%B1%A2_%E1%B1%A0%E1%B1%9F%E1%B1%B9%E1%B1%B4%E1%B1%A9%E1%B1%B5 "ᱦᱟᱲᱟᱢ ᱠᱟᱹᱴᱩᱵ – Santali") - [Scots](https://sco.wikipedia.org/wiki/Thoum "Thoum – Scots") - [Sicilianu](https://scn.wikipedia.org/wiki/Puseri "Puseri – Sicilian") - [سنڌي](https://sd.wikipedia.org/wiki/%D8%A2%DA%B1%D9%88%D9%BA%D9%88 "آڱوٺو – Sindhi") - [Slovenčina](https://sk.wikipedia.org/wiki/Palec_(prst) "Palec (prst) – Slovak") - [Soomaaliga](https://so.wikipedia.org/wiki/Suul "Suul – Somali") - [کوردی](https://ckb.wikipedia.org/wiki/%D8%A6%DB%95%D8%B3%D9%BE%DB%8E_%DA%A9%D9%88%DA%98%DB%95 "ئەسپێ کوژە – Central Kurdish") - [Српски / srpski](https://sr.wikipedia.org/wiki/%D0%9F%D0%B0%D0%BB%D0%B0%D1%86 "Палац – Serbian") - [Srpskohrvatski / српскохрватски](https://sh.wikipedia.org/wiki/Palac "Palac – Serbo-Croatian") - [Sunda](https://su.wikipedia.org/wiki/Indung_leungeun "Indung leungeun – Sundanese") - [Suomi](https://fi.wikipedia.org/wiki/Peukalo "Peukalo – Finnish") - [Svenska](https://sv.wikipedia.org/wiki/Tumme "Tumme – Swedish") - [Tagalog](https://tl.wikipedia.org/wiki/Hinlalaki "Hinlalaki – Tagalog") - [தமிழ்](https://ta.wikipedia.org/wiki/%E0%AE%AA%E0%AF%86%E0%AE%B0%E0%AF%81_%E0%AE%B5%E0%AE%BF%E0%AE%B0%E0%AE%B2%E0%AF%8D "பெரு விரல் – Tamil") - [తెలుగు](https://te.wikipedia.org/wiki/%E0%B0%AC%E0%B1%8A%E0%B0%9F%E0%B0%A8_%E0%B0%B5%E0%B1%87%E0%B0%B2%E0%B1%81 "బొటన వేలు – Telugu") - [ไทย](https://th.wikipedia.org/wiki/%E0%B8%99%E0%B8%B4%E0%B9%89%E0%B8%A7%E0%B8%AB%E0%B8%B1%E0%B8%A7%E0%B9%81%E0%B8%A1%E0%B9%88%E0%B8%A1%E0%B8%B7%E0%B8%AD "นิ้วหัวแม่มือ – Thai") - [Türkçe](https://tr.wikipedia.org/wiki/Ba%C5%9Fparmak "Başparmak – Turkish") - [Tyap](https://kcg.wikipedia.org/wiki/A%CC%B1turugbak_mbwak "A̱turugbak mbwak – Tyap") - [Українська](https://uk.wikipedia.org/wiki/%D0%92%D0%B5%D0%BB%D0%B8%D0%BA%D0%B8%D0%B9_%D0%BF%D0%B0%D0%BB%D0%B5%D1%86%D1%8C "Великий палець – Ukrainian") - [اردو](https://ur.wikipedia.org/wiki/%D8%A7%D9%86%DA%AF%D9%88%D9%B9%DA%BE%D8%A7 "انگوٹھا – Urdu") - [ئۇيغۇرچە / Uyghurche](https://ug.wikipedia.org/wiki/%D8%A8%D8%A7%D8%B4_%D8%A8%D8%A7%D8%B1%D9%85%D8%A7%D9%82 "باش بارماق – Uyghur") - [Tiếng Việt](https://vi.wikipedia.org/wiki/Ng%C3%B3n_c%C3%A1i "Ngón cái – Vietnamese") - [Võro](https://fiu-vro.wikipedia.org/wiki/P%C3%A4kk "Päkk – Võro") - [Walon](https://wa.wikipedia.org/wiki/P%C3%B4ce "Pôce – Walloon") - [Winaray](https://war.wikipedia.org/wiki/Tamuragk%C3%B4 "Tamuragkô – Waray") - [吴语](https://wuu.wikipedia.org/wiki/%E6%8B%87%E6%8C%87 "拇指 – Wu") - [Yorùbá](https://yo.wikipedia.org/wiki/%C3%80t%C3%A0np%C3%A0k%C3%B2 "Àtànpàkò – Yoruba") - [粵語](https://zh-yue.wikipedia.org/wiki/%E6%89%8B%E6%8C%87%E5%85%AC "手指公 – Cantonese") - [中文](https://zh.wikipedia.org/wiki/%E6%8B%87%E6%8C%87 "拇指 – Chinese") - [Betawi](https://bew.wikipedia.org/wiki/Jempol "Jempol – Betawi") [Edit links](https://www.wikidata.org/wiki/Special:EntityPage/Q83360#sitelinks-wikipedia "Edit interlanguage links") - [Article](/wiki/Thumb "View the content page [c]") - [Talk](/wiki/Talk:Thumb "Discuss improvements to the content page [t]") English - [Read](/wiki/Thumb) - [Edit](/w/index.php?title=Thumb&action=edit "Edit this page [e]") - [View history](/w/index.php?title=Thumb&action=history "Past revisions of this page [h]") Tools Tools move to sidebar hide Actions - [Read](/wiki/Thumb) - [Edit](/w/index.php?title=Thumb&action=edit "Edit this page [e]") - [View history](/w/index.php?title=Thumb&action=history) General - [What links here](/wiki/Special:WhatLinksHere/Thumb "List of all English Wikipedia pages containing links to this page [j]") - [Related changes](/wiki/Special:RecentChangesLinked/Thumb "Recent changes in pages linked from this page [k]") - [Upload file](//en.wikipedia.org/wiki/Wikipedia:File_Upload_Wizard "Upload files [u]") - [Permanent link](/w/index.php?title=Thumb&oldid=1274819517 "Permanent link to this revision of this page") - [Page information](/w/index.php?title=Thumb&action=info "More information about this page") - [Cite this page](/w/index.php?title=Special:CiteThisPage&page=Thumb&id=1274819517&wpFormIdentifier=titleform "Information on how to cite this page") - [Get shortened URL](/w/index.php?title=Special:UrlShortener&url=https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FThumb) - [Download QR code](/w/index.php?title=Special:QrCode&url=https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FThumb) Print/export - [Download as PDF](/w/index.php?title=Special:DownloadAsPdf&page=Thumb&action=show-download-screen "Download this page as a PDF file") - [Printable version](/w/index.php?title=Thumb&printable=yes "Printable version of this page [p]") In other projects - [Wikimedia Commons](https://commons.wikimedia.org/wiki/Category:Thumbs) - [Wikidata item](https://www.wikidata.org/wiki/Special:EntityPage/Q83360 "Structured data on this page hosted by Wikidata [g]") Appearance move to sidebar hide From Wikipedia, the free encyclopedia First digit of the hand This article is about the digit of the hand. For other uses, see [Thumb (disambiguation)](/wiki/Thumb_(disambiguation) "Thumb (disambiguation)"). [TABLE] The **thumb** is the first [digit](/wiki/Digit_(anatomy) "Digit (anatomy)") of the [hand](/wiki/Hand "Hand"), next to the [index finger](/wiki/Index_finger "Index finger").^([\[A\]](#cite_note-2)) When a person is standing in the medical [anatomical position](/wiki/Anatomical_position "Anatomical position") (where the palm is facing to the front), the thumb is the outermost digit. The Medical Latin English noun for thumb is [*pollex*](https://en.wiktionary.org/wiki/pollex "wikt:pollex") (compare [*hallux*](/wiki/Toe#Hallux "Toe") for big toe), and the corresponding adjective for thumb is [*pollical*](https://en.wiktionary.org/wiki/pollical "wikt:pollical"). ## Definition \[[edit](/w/index.php?title=Thumb&action=edit§ion=1 "Edit section: Definition")\] [TABLE] ### Thumb and fingers \[[edit](/w/index.php?title=Thumb&action=edit§ion=2 "Edit section: Thumb and fingers")\] The English word *finger* has two [senses](/wiki/Finger_numbering "Finger numbering"), even in the context of appendages of a single typical human hand: 1) Any of the five terminal members of the hand. 2) Any of the four terminal members of the hand, other than the thumb.^([\[2\]](#cite_note-3)) 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](/wiki/Proto-Indo-European_language "Proto-Indo-European language"), a suffixed form of \**penkwe* (or \**penqe*), which has given rise to many [Indo-European](/wiki/Indo-European_languages "Indo-European languages")-family words (tens of them defined in English dictionaries) that involve, or stem from, concepts of fiveness. The thumb shares the following with each of the other four fingers: - Having a skeleton of [phalanges](/wiki/Phalanges "Phalanges"), joined by hinge-like joints that provide flexion toward the palm of the hand - Having a dorsal surface that features hair and a nail, and a hairless palmar aspect with [fingerprint](/wiki/Fingerprint "Fingerprint") ridges The thumb contrasts with each of the other four fingers by being the only one that: - Is opposable to the other four fingers - Has two [phalanges](/wiki/Phalanges "Phalanges") rather than three. However, recently there have been reports that the thumb, like other fingers, has three phalanges, but lacks a metacarpal bone.^([\[3\]](#cite_note-4)) - Has greater breadth in the [distal](/wiki/Distal "Distal") phalanx than in the [proximal](/wiki/Proximal "Proximal") phalanx - Is attached to such a mobile [metacarpus](/wiki/Metacarpus "Metacarpus") (which produces most of the opposability) - Curls horizontally instead of vertically and 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. ## Opposition and apposition \[[edit](/w/index.php?title=Thumb&action=edit§ion=3 "Edit section: Opposition and apposition")\] ### Humans \[[edit](/w/index.php?title=Thumb&action=edit§ion=4 "Edit section: Humans")\] Anatomists and other researchers focused on human anatomy have hundreds of definitions of *opposition*.^([\[4\]](#cite_note-vanNierop-2008-5)) Some anatomists^([\[5\]](#cite_note-Brownetal-2004-6)) 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*. To anatomists, this makes sense as two intrinsic hand muscles are named for this specific movement (the [opponens pollicis](/wiki/Opponens_pollicis_muscle "Opponens pollicis muscle") and [opponens digiti minimi](/wiki/Opponens_digiti_minimi_muscle "Opponens digiti minimi muscle") respectively). Other researchers use another definition,^([\[4\]](#cite_note-vanNierop-2008-5)) 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*. Moving a limb back to its neutral position is called reposition and a rotary movement is referred to as [circumduction](/wiki/Circumduction_(anatomy) "Circumduction (anatomy)"). Primatologists and hand research pioneers [John](/wiki/John_Napier_(primatologist) "John Napier (primatologist)") and [Prudence Napier](/wiki/Prudence_Hero_Napier "Prudence Hero 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](/wiki/Carpometacarpal_joint "Carpometacarpal joint")).^([\[6\]](#cite_note-Primates-FAQ-7)) Arguably, this definition was chosen to underline what is unique to the human thumb. ### Other primates \[[edit](/w/index.php?title=Thumb&action=edit§ion=5 "Edit section: Other primates")\] [![](//upload.wikimedia.org/wikipedia/commons/thumb/0/00/BonoboFishing02_cropped.jpeg/220px-BonoboFishing02_cropped.jpeg)](/wiki/File:BonoboFishing02_cropped.jpeg) A [bonobo](/wiki/Bonobo "Bonobo") "fishing" for termites, an example of incomplete/"untrue" opposition^([\[7\]](#cite_note-8)\[*[better source needed](/wiki/Wikipedia:NOTRS "Wikipedia:NOTRS")*\]) - [Primates](/wiki/Primate "Primate") fall into one of six groups:^([\[8\]](#cite_note-PrimateAnatomy8-9)) - Thumbless: [spider monkey](/wiki/Spider_monkey "Spider monkey") and [colobus](/wiki/Colobus "Colobus") - Nonopposable thumbs: [tarsiers](/wiki/Tarsier "Tarsier") (which are found in the islands of Southeast Asia), [marmosets](/wiki/Marmoset "Marmoset") (which are [New World monkeys](/wiki/New_World_monkeys "New World monkeys")) - Pseudo-opposable thumbs: all [strepsirrhines](/wiki/Strepsirrhine "Strepsirrhine") (lemurs, pottos and lorises) and [Cebidae](/wiki/Cebidae "Cebidae") (capuchin and squirrel monkeys, which are [New World monkeys](/wiki/New_World_monkeys "New World monkeys")) - Opposable thumbs: [Old World monkeys](/wiki/Old_World_monkey "Old World monkey") (Circopithecidae) except colobus, and all [great apes](/wiki/Hominidae "Hominidae") - Opposable with comparatively long thumbs: [gibbons](/wiki/Gibbon "Gibbon") (or lesser apes) - Yet to be classified: other [New World monkeys](/wiki/New_World_monkeys "New World monkeys") ([tamarins](/wiki/Tamarin "Tamarin"), Aotidae: night or owl monkeys, Pitheciidae: titis, sakis and uakaris, Atelidae: howler and woolly monkeys) The spider monkey compensates for being virtually thumbless by using the hairless part of its long, prehensile tail for grabbing objects. In [apes](/wiki/Ape "Ape") and [Old World monkeys](/wiki/Old_World_monkeys "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.^([\[9\]](#cite_note-Jones-Lederman-2006-p12-10)) *[Darwinius masillae](/wiki/Darwinius "Darwinius")*, an [Eocene](/wiki/Eocene "Eocene") primate [transitional fossil](/wiki/Transitional_fossil "Transitional fossil") between [prosimian](/wiki/Prosimian "Prosimian") and [simian](/wiki/Simian "Simian"), had hands and feet with highly flexible digits featuring opposable thumbs and halluces.^([\[10\]](#cite_note-PloS-Darwinius-2009-11)) ### Other placental mammals \[[edit](/w/index.php?title=Thumb&action=edit§ion=6 "Edit section: Other placental mammals")\] - [Giant pandas](/wiki/Giant_panda "Giant panda") — five clawed fingers plus an extra-long [sesamoid bone](/wiki/Sesamoid_bone#Panda_anatomy "Sesamoid bone") beside the true first finger that, though not a true finger, works like an opposable thumb.^([\[11\]](#cite_note-12)) - Most [rodents](/wiki/Rodents "Rodents") have a partly opposable toe on each front paw, letting them grasp.^([\[12\]](#cite_note-order-13)) - In some *[mice](/wiki/Muridae "Muridae")*, the hallux ("big toe") is clawless and fully opposable, including [arboreal](/wiki/Arboreal "Arboreal") species such as *[Hapalomys](/wiki/Hapalomys "Hapalomys")*, *[Chiropodomys](/wiki/Chiropodomys "Chiropodomys")*, *[Vandeleuria](/wiki/Vandeleuria "Vandeleuria")*, and *[Chiromyscus](/wiki/Chiromyscus "Chiromyscus")*; and [saltatorial](/wiki/Saltatorial "Saltatorial"), bipedal species such as *[Notomys](/wiki/Notomys "Notomys")* and possibly some [Gerbillinae](/wiki/Gerbillinae "Gerbillinae").^([\[13\]](#cite_note-14)) - The East African [maned rat](/wiki/Maned_rat "Maned rat") (*Lophiomys imhausi*), an arboreal, porcupine-like rodent, has four fingers on its hands and feet and a partially opposable thumb.^([\[14\]](#cite_note-15)) Additionally, in many [polydactyl cats](/wiki/Polydactyl_cats "Polydactyl cats"), both the [innermost toe](/wiki/Innermost_toe "Innermost toe") and [outermost toe](/wiki/Outermost_toe "Outermost toe") ([pinky](/wiki/Little_finger "Little finger")) may become opposable, allowing the cat to perform more complex tasks.^(\[*[citation\ needed](/wiki/Wikipedia:Citation_needed "Wikipedia:Citation needed")*\]) ### Marsupials \[[edit](/w/index.php?title=Thumb&action=edit§ion=7 "Edit section: Marsupials")\] [![](//upload.wikimedia.org/wikipedia/commons/thumb/f/fa/Ailurops_ursinus_Naemundung_5_North_Sulawesi_cropped.JPG/105px-Ailurops_ursinus_Naemundung_5_North_Sulawesi_cropped.JPG)](/wiki/File:Ailurops_ursinus_Naemundung_5_North_Sulawesi_cropped.JPG) [![](//upload.wikimedia.org/wikipedia/commons/thumb/5/57/Oppossumthumb.jpg/180px-Oppossumthumb.jpg)](/wiki/File:Oppossumthumb.jpg) Left: Opposable toes of the [Sulawesi bear cuscus](/wiki/Sulawesi_bear_cuscus "Sulawesi bear cuscus") forelimb Right: Opposable thumb on rear foot of an opossum - In most [phalangerid](/wiki/Phalangerid "Phalangerid") [marsupials](/wiki/Marsupial "Marsupial") (a family of [possums](/wiki/Phalangeriformes "Phalangeriformes")) except species *[Trichosurus](/wiki/Trichosurus "Trichosurus")* and *[Wyulda](/wiki/Wyulda "Wyulda")*, the first and second toes of the forefoot are opposable to the other three. In the hind foot, the first toe is clawless but opposable and provides firm grip on branches. The second and third toes are partly [syndactylous](/wiki/Dactyly "Dactyly"), united by skin at the top joint while the two separate nails serve as hair combs. The fourth and fifth toes are the largest of the hind foot.^([\[15\]](#cite_note-Nowak-1999-16)) - [Koalas](/wiki/Koala "Koala") have five toes on their fore and hind feet with sharp curved claws except for the first toe of the hind foot. The first and second toes of the forefeet are opposable to the other three, which enables the koala to grip smaller branches and search for fresh leaves in the outer canopy. Similar to the phalangerids, the second and third toes of the hind foot are fused but have separate claws.^([\[16\]](#cite_note-McDade-2003-koala-17)) - [Opossums](/wiki/Opossum "Opossum") are New World marsupials with opposable thumbs in the hind feet giving these animals their characteristic grasping capability (with the exception of the [water opossum](/wiki/Water_opossum "Water opossum"), the webbed feet of which restrict opposability).^([\[17\]](#cite_note-McDade-2003-opossum-18)) - The mouse-like [microbiotheres](/wiki/Microbiotheria "Microbiotheria") were a group of South American marsupials most closely related to Australian marsupials. The only extant member, *[Dromiciops gliroides](/wiki/Monito_del_Monte "Monito del Monte")*, is not closely related to opossums but has paws similar to these animals, each having opposable toes adapted for gripping.^([\[18\]](#cite_note-McDade-2003-microbiotheres-19)) ### Reptiles \[[edit](/w/index.php?title=Thumb&action=edit§ion=8 "Edit section: Reptiles")\] - The front feet of [chameleons](/wiki/Chameleons "Chameleons") are organized into a medial bundle of toes 1, 2 and 3, and a lateral bundle of toes 4 and 5, and the hind feet are organized into a medial bundle of toes 1 and 2, and a lateral bundle of toes 3, 4 and 5.^([\[19\]](#cite_note-20)) ### Dinosaurs \[[edit](/w/index.php?title=Thumb&action=edit§ion=9 "Edit section: Dinosaurs")\] - Dinosaurs belonging to the family of bird-like dinosaur [Troodontidae](/wiki/Troodontidae "Troodontidae") had a partially opposable finger. It is possible that this adaptation was used to better manipulate ground objects or moving undergrowth branches when searching for prey.^([\[20\]](#cite_note-russell1982-21)) - The small predatory dinosaur *[Bambiraptor](/wiki/Bambiraptor "Bambiraptor")* may have had mutually opposable first and third fingers and a forelimb manoeuvrability that would allow the hand to reach its mouth. Its forelimb morphology and range of motion enabled two-handed prehension, one-handed clutching of objects to the chest, and use of the hand as a hook.^([\[21\]](#cite_note-22)) - *[Nqwebasaurus](/wiki/Nqwebasaurus "Nqwebasaurus")* — a [coelurosaur](/wiki/Coelurosaur "Coelurosaur") with a long, three-fingered hand which included a partially opposable thumb (a "killer claw").^([\[22\]](#cite_note-23)) In addition to these, some other dinosaurs may have had partially or completely opposed toes in order to manipulate food and/or grasp prey. #### Birds \[[edit](/w/index.php?title=Thumb&action=edit§ion=10 "Edit section: Birds")\] [![](//upload.wikimedia.org/wikipedia/commons/thumb/d/d7/Bird-feets-en.svg/220px-Bird-feets-en.svg.png)](/wiki/File:Bird-feets-en.svg) Four types of bird feet (right foot diagrams) See also: [Dactyly § Anisodactyly](/wiki/Dactyly#Anisodactyly "Dactyly") - Most [birds](/wiki/Bird "Bird") have at least one opposable toe on the foot, in [various configurations](/wiki/Dactyly#In_birds "Dactyly"), though these are seldom called "thumbs". They are more often known simply as [halluxes](/wiki/Toe#Hallux "Toe"). #### Pterosaurs \[[edit](/w/index.php?title=Thumb&action=edit§ion=11 "Edit section: Pterosaurs")\] - The [wukongopterid](/wiki/Wukongopteridae "Wukongopteridae") pterosaur *[Kunpengopterus](/wiki/Kunpengopterus "Kunpengopterus")* bore an opposable first toe on each wing. The presence of opposable thumbs in this taxon is thought to be an arboreal adaptation.^([\[23\]](#cite_note-Zhouetal2021-24)) ### Amphibians \[[edit](/w/index.php?title=Thumb&action=edit§ion=12 "Edit section: Amphibians")\] - *[Phyllomedusa](/wiki/Phyllomedusa "Phyllomedusa")*, a genus of frogs native to South America.^([\[24\]](#cite_note-Phyllomedusa-25)) ## Human anatomy \[[edit](/w/index.php?title=Thumb&action=edit§ion=13 "Edit section: Human anatomy")\] ### Skeleton \[[edit](/w/index.php?title=Thumb&action=edit§ion=14 "Edit section: Skeleton")\] The skeleton of the thumb consists of the [first metacarpal bone](/wiki/First_metacarpal_bone "First metacarpal bone") which articulates [proximally](/wiki/Proximal "Proximal") with the [carpus](/wiki/Carpal_bones "Carpal bones") at the [carpometacarpal joint](/wiki/Articulatio_carpometacarpea_pollicis "Articulatio carpometacarpea pollicis") and [distally](/wiki/Distal "Distal") with the [proximal phalanx](/wiki/Proximal_phalanges "Proximal phalanges") at the [metacarpophalangeal joint](/wiki/Metacarpophalangeal_joint "Metacarpophalangeal joint"). This latter bone articulates with the [distal phalanx](/wiki/Distal_phalanges "Distal phalanges") at the [interphalangeal joint](/wiki/Interphalangeal_articulations_of_hand "Interphalangeal articulations of hand"). Additionally, there are two [sesamoid bones](/wiki/Sesamoid_bone "Sesamoid bone") at the metacarpophalangeal joint. ### Muscles \[[edit](/w/index.php?title=Thumb&action=edit§ion=15 "Edit section: Muscles")\] Main article: [Muscles of the thumb](/wiki/Muscles_of_the_thumb "Muscles of the thumb") The muscles of the thumb can be compared to [guy-wires](/wiki/Guy-wire "Guy-wire") supporting a flagpole; tension from these muscular guy-wires must be provided in all directions to maintain stability in the articulated column formed by the bones of the thumb. Because this stability is actively maintained by muscles rather than by articular constraints, most muscles attached to the thumb tend to be active during most thumb motions.^([\[25\]](#cite_note-26)) The muscles acting on the thumb can be divided into two groups: The extrinsic hand muscles, with their muscle bellies located in the forearm, and the intrinsic hand muscles, with their muscle bellies located in the hand proper.^([\[26\]](#cite_note-27)) #### Extrinsic \[[edit](/w/index.php?title=Thumb&action=edit§ion=16 "Edit section: Extrinsic")\] [![](//upload.wikimedia.org/wikipedia/commons/thumb/d/dc/Musculus_flexor_pollicis_longus.png/85px-Musculus_flexor_pollicis_longus.png)](/wiki/File:Musculus_flexor_pollicis_longus.png) [![](//upload.wikimedia.org/wikipedia/commons/thumb/1/1b/Gray419.png/100px-Gray419.png)](/wiki/File:Gray419.png) Flexor pollicis longus (left) and deep muscles of dorsal forearm (right) A [ventral](/wiki/Ventral "Ventral") forearm muscle, the [flexor pollicis longus](/wiki/Flexor_pollicis_longus_muscle "Flexor pollicis longus muscle") (FPL) originates on the anterior side of the [radius](/wiki/Radius_(bone) "Radius (bone)") distal to the [radial tuberosity](/wiki/Radial_tuberosity "Radial tuberosity") and from the [interosseous membrane](/wiki/Interosseous_membrane_of_forearm "Interosseous membrane of forearm"). It passes through the [carpal tunnel](/wiki/Carpal_tunnel "Carpal tunnel") in a separate [tendon sheath](/wiki/Tendon_sheath "Tendon sheath"), after which it lies between the heads of the flexor pollicis brevis. It finally attaches onto the base of the distal phalanx of the thumb. It is innervated by the [anterior interosseus branch](/wiki/Anterior_interosseous_nerve "Anterior interosseous nerve") of the [median nerve](/wiki/Median_nerve "Median nerve") (C7-C8)^([\[27\]](#cite_note-Platzer-162-28)) It is a persistence of one of the former [contrahentes](/wiki/Contrahentes "Contrahentes") muscles that pulled the fingers or toes together. Three dorsal forearm muscles act on the thumb: The [abductor pollicis longus](/wiki/Abductor_pollicis_longus_muscle "Abductor pollicis longus muscle") (APL) originates on the dorsal sides of both the [ulna](/wiki/Ulna "Ulna") and the radius, and from the interosseous membrane. Passing through the first tendon compartment, it inserts to the base of the first [metacarpal bone](/wiki/Metacarpus "Metacarpus"). A part of the tendon reaches the trapezium, while another fuses with the tendons of the extensor pollicis brevis and the abductor pollicis brevis. Except for abducting the hand, it flexes the hand towards the palm and abducts it radially. It is innervated by the [deep branch of the radial nerve](/wiki/Deep_branch_of_the_radial_nerve "Deep branch of the radial nerve") (C7-C8).^([\[28\]](#cite_note-Platzer-168-29)) The [extensor pollicis longus](/wiki/Extensor_pollicis_longus_muscle "Extensor pollicis longus muscle") (EPL) originates on the dorsal side of the ulna and the interosseous membrane. Passing through the third tendon compartment, it is inserted onto the base of the distal phalanx of the thumb. It uses the dorsal tubercle on the lower extremity of the radius as a [fulcrum](/wiki/Lever "Lever") to extend the thumb and also dorsiflexes and abducts the hand at the wrist. It is innervated by the [deep branch of the radial nerve](/wiki/Deep_branch_of_the_radial_nerve "Deep branch of the radial nerve") (C7-C8).^([\[28\]](#cite_note-Platzer-168-29)) The [extensor pollicis brevis](/wiki/Extensor_pollicis_brevis_muscle "Extensor pollicis brevis muscle") (EPB) originates on the ulna distal to the abductor pollicis longus, from the interosseus membrane, and from the dorsal side of the radius. Passing through the first tendon compartment together with the abductor pollicis longus, it is attached to the base of the proximal phalanx of the thumb. It extends the thumb and, because of its close relationship to the long abductor, also abducts the thumb. It is innervated by the [deep branch of the radial nerve](/wiki/Deep_branch_of_the_radial_nerve "Deep branch of the radial nerve") (C7-T1).^([\[28\]](#cite_note-Platzer-168-29)) The tendons of the extensor pollicis longus and extensor pollicis brevis form what is known as the [anatomical snuff box](/wiki/Anatomical_snuff_box "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). #### Intrinsic \[[edit](/w/index.php?title=Thumb&action=edit§ion=17 "Edit section: Intrinsic")\] [![](//upload.wikimedia.org/wikipedia/commons/thumb/2/27/Gray426.png/160px-Gray426.png)](/wiki/File:Gray426.png) [![](//upload.wikimedia.org/wikipedia/commons/thumb/2/29/Gray428.png/100px-Gray428.png)](/wiki/File:Gray428.png) Thenar (left) and dorsal interossei (right) muscles There are three [thenar muscles](/wiki/Thenar_eminence "Thenar eminence"): The [abductor pollicis brevis](/wiki/Abductor_pollicis_brevis_muscle "Abductor pollicis brevis muscle") (APB) originates on the [scaphoid tubercle](/wiki/Scaphoid_bone "Scaphoid bone") and the [flexor retinaculum](/wiki/Flexor_retinaculum_of_the_hand "Flexor retinaculum of the hand"). It inserts to the radial sesamoid bone and the proximal phalanx of the thumb. It is innervated by the [median nerve](/wiki/Median_nerve "Median nerve") (C8-T1).^([\[29\]](#cite_note-Platzer-176-30)) The [flexor pollicis brevis](/wiki/Flexor_pollicis_brevis_muscle "Flexor pollicis brevis muscle") (FPB) has two heads. The superficial head arises on the flexor retinaculum, while the deep head originates on three carpal bones: the [trapezium](/wiki/Trapezium_(bone) "Trapezium (bone)"), [trapezoid](/wiki/Trapezoid_bone "Trapezoid bone"), and [capitate](/wiki/Capitate_bone "Capitate bone"). The muscle is inserted onto the radial sesamoid bone of the metacarpophalangeal joint. It acts to flex, adduct, and abduct the thumb, and is therefore also able to oppose the thumb. The superficial head is innervated by the [median nerve](/wiki/Median_nerve "Median nerve"), while the deep head is innervated by the [ulnar nerve](/wiki/Ulnar_nerve "Ulnar nerve") (C8-T1).^([\[29\]](#cite_note-Platzer-176-30)) The [opponens pollicis](/wiki/Opponens_pollicis_muscle "Opponens pollicis muscle") originates on the tubercle of the trapezium and the flexor retinaculum. It is inserted onto the radial side of the first metacarpal. It opposes the thumb and assists in adduction. It is innervated by the [median nerve](/wiki/Median_nerve "Median nerve").^([\[29\]](#cite_note-Platzer-176-30)) Other muscles involved are: The [adductor pollicis](/wiki/Adductor_pollicis_muscle "Adductor pollicis muscle") also has two heads. The transversal head originates along the entire third metacarpal bone, while the oblique head originates on the carpal bones proximal to the third metacarpal. The muscle is inserted onto the ulnar sesamoid bone of the metacarpophalangeal joint. It adducts the thumb, and assists in opposition and flexion. It is innervated by the deep branch of the [ulnar nerve](/wiki/Ulnar_nerve "Ulnar nerve") (C8-T1).^([\[29\]](#cite_note-Platzer-176-30)) The first [dorsal interosseous](/wiki/Dorsal_interossei_of_the_hand "Dorsal interossei of the hand"), one of the central muscles of the hand, extends from the base of the thumb metacarpal to the radial side of the proximal phalanx of the index finger.^([\[30\]](#cite_note-Platzer-174-31)) ### Variations \[[edit](/w/index.php?title=Thumb&action=edit§ion=18 "Edit section: Variations")\] Further information: [Hitchhiker's thumb](/wiki/Hitchhiker%27s_thumb "Hitchhiker's thumb"), [brachydactyly type D](/wiki/Brachydactyly_type_D "Brachydactyly type D"), [triphalangeal thumb](/wiki/Triphalangeal_thumb "Triphalangeal thumb"), and [polydactyly](/wiki/Polydactyly "Polydactyly") [![](//upload.wikimedia.org/wikipedia/commons/thumb/4/42/Hitchhikers_thumb.jpg/220px-Hitchhikers_thumb.jpg)](/wiki/File:Hitchhikers_thumb.jpg) [Hitchhiker's thumb](/wiki/Hitchhiker%27s_thumb "Hitchhiker's thumb") There is a variation of the human thumb where the angle between the first and second (proximal and distal) [phalanges](/wiki/Distal_phalanges "Distal phalanges") varies between 0° and almost 90° when the thumb is in a [thumbs-up](/wiki/Thumbs_Up "Thumbs Up") gesture.^([\[31\]](#cite_note-hitchthumbmyth-32)) It has been suggested that the variation is an autosomal [recessive trait](/wiki/Recessive_trait "Recessive trait"), called a [hitchhiker's thumb](/wiki/Hitchhiker%27s_thumb "Hitchhiker's thumb"), with [homozygous](/wiki/Homozygous "Homozygous") carriers having an angle close to 90°.^([\[32\]](#cite_note-33)) However this theory has been disputed, since the variation in thumb angle is known to fall on a continuum and shows little evidence of the [bi-modality](/wiki/Bimodal_distribution "Bimodal distribution") seen in other recessive genetic traits.^([\[31\]](#cite_note-hitchthumbmyth-32)) Other variations of the thumb include [brachydactyly type D](/wiki/Brachydactyly_type_D "Brachydactyly type D") (which is a thumb with a congenitally short distal phalanx), a [triphalangeal thumb](/wiki/Triphalangeal_thumb "Triphalangeal thumb") (which is a thumb which has 3 phalanges instead of the usual two), and [polysyndactyly](/wiki/Polysyndactyly "Polysyndactyly") (which is a combination of radial polydactyly and syndactyly). ### Grips \[[edit](/w/index.php?title=Thumb&action=edit§ion=19 "Edit section: Grips")\] [![](//upload.wikimedia.org/wikipedia/commons/thumb/3/39/Gripclosed.jpg/130px-Gripclosed.jpg)](/wiki/File:Gripclosed.jpg) [![](//upload.wikimedia.org/wikipedia/commons/thumb/b/bd/Iverson_grip_1950.jpg/120px-Iverson_grip_1950.jpg)](/wiki/File:Iverson_grip_1950.jpg) Left: In a power grip the object is in contact with the palm. Right: Cricketer [Jack Iverson's](/wiki/Jack_Iverson "Jack Iverson") "bent finger grip", an unusual pad-to-side precision grip designed to confuse batsmen. One of the earlier significant contributors to the study of hand grips was orthopedic primatologist and paleoanthropologist [John Napier](/wiki/John_Napier_(primatologist) "John Napier (primatologist)"), who proposed organizing the movements of the hand by their anatomical basis as opposed to work done earlier that had only used arbitrary classification.^([\[33\]](#cite_note-34)) Most of this early work on hand grips had a pragmatic basis as it was intended to narrowly define compensable injuries to the hand, which required an understanding of the anatomical basis of hand movement. Napier proposed two primary [prehensile](/wiki/Prehensile "Prehensile") grips: the *precision grip* and the *power grip*.^([\[34\]](#cite_note-35)) The precision and power grip are defined by the position of the thumb and fingers where: - The **power grip** is when the fingers (and sometimes palm) clamp down on an object with the thumb making counter pressure. Examples of the power grip are gripping a hammer, opening a jar using *both your palm and fingers*, and during pullups. - The **precision grip** is when the intermediate and distal phalanges ("fingertips") and the thumb press against each other. Examples of a precision grip are writing with a pencil, opening a jar *with the fingertips alone*, and gripping a ball (only if the ball is not tight against the palm). [![](//upload.wikimedia.org/wikipedia/commons/thumb/7/71/Distal-phalanges-thumb-index_Journal.pone.0011727.g001.png/220px-Distal-phalanges-thumb-index_Journal.pone.0011727.g001.png)](/wiki/File:Distal-phalanges-thumb-index_Journal.pone.0011727.g001.png) Thumb and index finger during pad-to-pad precision grasping^([\[35\]](#cite_note-PLOS-2010-36)) Opposability of the thumb should not be confused with a precision grip as some animals possess semi-opposable thumbs yet are known to have extensive precision grips ([Tufted Capuchins](/wiki/Cebus_apella "Cebus apella") for example).^([\[36\]](#cite_note-37)) Nevertheless, precision grips are usually only found in higher apes, and only in degrees significantly more restricted than in humans.^([\[37\]](#cite_note-38)) The pad-to-pad pinch between the thumb and index finger is made possible because of the human ability to passively hyperextend the [distal phalanx](/wiki/Distal_phalanges "Distal phalanges") of the index finger. Most non-human primates have to flex their long fingers in order for the small thumb to reach them.^([\[9\]](#cite_note-Jones-Lederman-2006-p12-10)) In humans, the distal pads are wider than in other primates because the soft tissues of the finger tip are attached to a horseshoe-shaped edge on the underlying bone, and, in the grasping hand, the distal pads can therefore conform to uneven surfaces while pressure is distributed more evenly in the finger tips. The distal pad of the human thumb is divided into a proximal and a distal compartment, the former more deformable than the latter, which allows the thumb pad to mold around an object.^([\[9\]](#cite_note-Jones-Lederman-2006-p12-10)) In robotics, almost all [robotic hands](/wiki/Robotic_hand "Robotic hand") have a long and strong opposable thumb. Like human hands, the thumb of a robotic hand also plays a key role in gripping an object. One inspiring approach of robotic grip planning is to mimic human thumb placement. ^([\[38\]](#cite_note-39)) In a sense, human thumb placement indicates which surface or part of the object is good for grip. Then the robot places its thumb to the same location and plans the other fingers based on the thumb placement. The function of the thumb declines physiologically with aging. This can be demonstrated by assessing the motor sequencing of the thumb.^([\[39\]](#cite_note-40)) ## Human evolution \[[edit](/w/index.php?title=Thumb&action=edit§ion=20 "Edit section: Human evolution")\] A primitive autonomization of the first [carpometacarpal joint](/wiki/Carpometacarpal_joint "Carpometacarpal joint") (CMC) may have occurred in dinosaurs. A real differentiation appeared an estimated 70 mya in early primates, while the shape of the human thumb CMC finally appears about 5 mya. The result of this evolutionary process is a human CMC joint positioned at 80° of pronation, 40 of abduction, and 50° of flexion in relation to an axis passing through the second and third CMC joints.^([\[40\]](#cite_note-Brüser-167-41)) Opposable thumbs are shared by some [primates](/wiki/Primate "Primate"), including most [catarrhines](/wiki/Catarrhini "Catarrhini").^(\[*[citation\ needed](/wiki/Wikipedia:Citation_needed "Wikipedia:Citation needed")*\]) The climbing and suspensory behaviour in [orthograde](/wiki/Orthograde_posture "Orthograde posture") apes, such as [chimpanzees](/wiki/Common_chimpanzee "Common chimpanzee"), has resulted in elongated hands while the thumb has remained short. As a result, these primates are unable to perform the pad-to-pad grip associated with opposability. However, in [pronograde](/wiki/Pronograde "Pronograde") monkeys such as [baboons](/wiki/Baboon "Baboon"), an adaptation to a terrestrial lifestyle has led to reduced finger length and thus hand proportions similar to those of humans. Consequently, these primates have dexterous hands and are able to grasp objects using a pad-to-pad grip. It can thus be difficult to identify hand adaptations to manipulation-related tasks based solely on thumb proportions.^([\[41\]](#cite_note-Moyà-Solà-1999-42)) The evolution of the fully opposable thumb is usually associated with *[Homo habilis](/wiki/Homo_habilis "Homo habilis")*, a forerunner of *[Homo sapiens](/wiki/Homo_sapiens "Homo sapiens")*.^([\[42\]](#cite_note-43)) This, however, is the suggested result of evolution from *[Homo erectus](/wiki/Homo_erectus "Homo erectus")* (around 1 [mya](/wiki/Mya_(unit) "Mya (unit)")) via a series of intermediate [anthropoid](/wiki/Simian "Simian") stages, and is therefore a much more complicated link. Modern humans are unique in the musculature of their forearm and hand. Yet, they remain autapomorphic, meaning each muscle is found in one or more non-human primates. The extensor pollicis brevis and flexor pollicis longus allow modern humans to have great manipulative skills and strong flexion in the thumb.^([\[43\]](#cite_note-44)) However, a more likely scenario may be that the specialized precision gripping hand (equipped with opposable thumb) of *[Homo habilis](/wiki/Homo_habilis "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](/wiki/Homo_habilis "Homo habilis")*, an advanced grasping-capable hand was accompanied by facultative [bipedalism](/wiki/Bipedalism "Bipedalism"), possibly implying, assuming a co-opted evolutionary relationship exists, that the latter resulted from the former as obligate bipedalism was yet to follow.^([\[44\]](#cite_note-45)) Walking may have been a by-product of busy hands and not vice versa. [HACNS1](/wiki/HACNS1 "HACNS1") (also known as [Human Accelerated Region](/wiki/Human_accelerated_regions "Human accelerated regions") 2) is a [gene enhancer](/wiki/Enhancer_(genetics) "Enhancer (genetics)") "that may have contributed to the evolution of the uniquely opposable human thumb, and possibly also modifications in the [ankle](/wiki/Ankle "Ankle") or [foot](/wiki/Foot "Foot") that allow humans to [walk](/wiki/Walk "Walk") on two legs". Evidence to date shows that of the 110,000 gene enhancer sequences identified in the human [genome](/wiki/Genome "Genome"), HACNS1 has undergone the most change during the [human evolution](/wiki/Human_evolution "Human evolution") since the [chimpanzee–human last common ancestor](/wiki/Chimpanzee%E2%80%93human_last_common_ancestor "Chimpanzee–human last common ancestor").^([\[45\]](#cite_note-46)) ## See also \[[edit](/w/index.php?title=Thumb&action=edit§ion=21 "Edit section: See also")\] - [Pollicization](/wiki/Pollicization "Pollicization") - [Prehensility](/wiki/Prehensility "Prehensility") - [Thumb signal](/wiki/Thumb_signal "Thumb signal") - [Thumb twiddling](/wiki/Thumb_twiddling "Thumb twiddling") - [Thumb war](/wiki/Thumb_war "Thumb war") ## Notes \[[edit](/w/index.php?title=Thumb&action=edit§ion=22 "Edit section: Notes")\] 1. **[^](#cite_ref-1)** [clinicalconsiderations](http://www.wesnorman.com/clinicalconsiderations.htm) at The Anatomy Lesson by Wesley Norman (Georgetown University) 2. **[^](#cite_ref-3)** ["Definition of FINGER"](https://www.merriam-webster.com/dictionary/finger). *www.merriam-webster.com*. 2024-09-26. Retrieved 2024-09-30. 3. **[^](#cite_ref-4)** Haeri, Seyed Mohammad Jafar, et al. "Human thumb consists of three phalanges and lacks metacarpal? A morphometric study on the long bones of the hand." Surgical and Radiologic Anatomy 44.8 (2022): 1101-1109.[https://doi.org/10.1007/s00276-022-02986-9](https://doi.org/10.1007/s00276-022-02986-9) 4. ^ [^(***a***)](#cite_ref-vanNierop-2008_5-0) [^(***b***)](#cite_ref-vanNierop-2008_5-1) [van Nierop et al. 2008](#CITEREFvan_Nieropvan_der_HelmOverbeekeDjajadiningrat2008), p. 34 5. **[^](#cite_ref-Brownetal-2004_6-0)** [Brown et al. 2004](#CITEREFBrownFreemanCuccurulloFreeman2004) 6. **[^](#cite_ref-Primates-FAQ_7-0)** ["Primates FAQ: Do any primates have opposable thumbs?"](https://www.primates.com/faq/). Wisconsin Regional Primate Research Center. Retrieved 20 November 2010. 7. **[^](#cite_ref-8)** ["The Thumb is the Hero"](https://query.nytimes.com/gst/fullpage.html?res=9F04E3D8173BF932A25752C0A967948260). *The New York Times*. January 11, 1981. Retrieved 20 November 2010. “The "fishing rod" a chimp strips of leaves and pokes into a termite nest to bring up a snack is as far as he'll ever get toward orbiting the planets.” 8. **[^](#cite_ref-PrimateAnatomy8_9-0)** [Ankel-Simons 2007](#CITEREFAnkel-Simons2007), p. 345 9. ^ [^(***a***)](#cite_ref-Jones-Lederman-2006-p12_10-0) [^(***b***)](#cite_ref-Jones-Lederman-2006-p12_10-1) [^(***c***)](#cite_ref-Jones-Lederman-2006-p12_10-2) [Jones & Lederman 2006](#CITEREFJonesLederman2006), Evolutionary Development and Anatomy of the Hand, p. 12 10. **[^](#cite_ref-PloS-Darwinius-2009_11-0)** [Franzen et al. 2009](#CITEREFFranzenGingerichHabersetzerHurum2009), pp. 15–18 11. **[^](#cite_ref-12)** ["The Panda's Thumb"](http://www.athro.com/evo/pthumb.html). Athro. 2000. Retrieved 21 November 2010. 12. **[^](#cite_ref-order_13-0)** Stefoff, Rebecca (2008). [*The Rodent Order*](https://books.google.com/books?id=7Gle7-L46TYC&pg=PA63). Marshall Cavendish. pp. 62–63, 71–73. [ISBN](/wiki/ISBN_(identifier) "ISBN (identifier)") [978-0-7614-3073-5](/wiki/Special:BookSources/978-0-7614-3073-5 "Special:BookSources/978-0-7614-3073-5"). 13. **[^](#cite_ref-14)** [Ellerman 1941](#CITEREFEllerman1941), p. 2 14. **[^](#cite_ref-15)** Grzimek, Bernhard (2003). Hutchins, Michael; Kleiman, Devra G.; Geist, Valerius; et al. (eds.). [*Grzimek's Animal Life Encyclopedia, Vol 16, Mammals V*](https://archive.org/details/grzimeksanimalli0002grzi_c1l6/page/293/mode/2up) (2nd ed.). Farmington Hills, MI: Gale Group. p. 293. [ISBN](/wiki/ISBN_(identifier) "ISBN (identifier)") [978-0-7876-7750-3](/wiki/Special:BookSources/978-0-7876-7750-3 "Special:BookSources/978-0-7876-7750-3"). 15. **[^](#cite_ref-Nowak-1999_16-0)** [Nowak 1999](#CITEREFNowak1999), p. 89 16. **[^](#cite_ref-McDade-2003-koala_17-0)** [McDade 2003](#CITEREFMcDade2003), vol 13, p. 44 17. **[^](#cite_ref-McDade-2003-opossum_18-0)** [McDade 2003](#CITEREFMcDade2003), vol 12, p. 250 18. **[^](#cite_ref-McDade-2003-microbiotheres_19-0)** [McDade 2003](#CITEREFMcDade2003), vol 12, p. 274 19. **[^](#cite_ref-20)** Anderson, Christopher V. & Higham, Timothy E. (2014). "Chameleon anatomy". In Tolley, Krystal A. & Herrel, Anthony (eds.). *The Biology of Chameleons*. Berkeley: University of California Press. pp. 7–55. [ISBN](/wiki/ISBN_(identifier) "ISBN (identifier)") [9780520276055](/wiki/Special:BookSources/9780520276055 "Special:BookSources/9780520276055"). 20. **[^](#cite_ref-russell1982_21-0)** Russell, D. A.; Séguin, R. (1982). ["Reconstruction of the small Cretaceous theropod *Stenonychosaurus inequalis* and a hypothetical dinosauroid"](https://archive.org/details/syllogeus37nati). *Syllogeus*. **37**: 1–43. 21. **[^](#cite_ref-22)** [Senter 2006](#CITEREFSenter2006) 22. **[^](#cite_ref-23)** [de Klerk et al. 2000](#CITEREFde_KlerkForsterSampsonChinsamy2000), p. 327. *The left manus shows that the flexed digit I had the potential to partially oppose digits II and III.* 23. **[^](#cite_ref-Zhouetal2021_24-0)** Zhou, X.; Pêgas, R. V.; Ma, W.; Han, G.; Jin, X.; Leal, M. E. C.; Bonde, N.; Kobayashi, Y.; Lautenschlager, S.; Wei, X.; Shen, C.; Ji, S. (2021). ["A new darwinopteran pterosaur reveals arborealism and an opposed thumb"](https://doi.org/10.1016%2Fj.cub.2021.03.030). *[Current Biology](/wiki/Current_Biology "Current Biology")*. **31** (11): 2429–2436.e7. [Bibcode](/wiki/Bibcode_(identifier) "Bibcode (identifier)"):[2021CBio...31E2429Z](https://ui.adsabs.harvard.edu/abs/2021CBio...31E2429Z). [doi](/wiki/Doi_(identifier) "Doi (identifier)"):[10.1016/j.cub.2021.03.030](https://doi.org/10.1016%2Fj.cub.2021.03.030). [PMID](/wiki/PMID_(identifier) "PMID (identifier)") [33848460](https://pubmed.ncbi.nlm.nih.gov/33848460). 24. **[^](#cite_ref-Phyllomedusa_25-0)** Bertoluci, Jaime (18 December 2002). ["Pedal luring in the leaf-frog Phyllomedusa burmeisteri (Anura, Hylidae, Phyllomedusinae)"](https://doi.org/10.11606%2Fissn.2316-9079.v1i2p93-95). *Phyllomedusa: Journal of Herpetology*. **1** (2): 93. [doi](/wiki/Doi_(identifier) "Doi (identifier)"):[10.11606/issn.2316-9079.v1i2p93-95](https://doi.org/10.11606%2Fissn.2316-9079.v1i2p93-95). 25. **[^](#cite_ref-26)** [Austin 2005](#CITEREFAustin2005), p. 339 26. **[^](#cite_ref-27)** ["Muscles of the thumb"](http://www.eatonhand.com/mus/mus131.htm). Eaton hand. Retrieved 11 May 2010. 27. **[^](#cite_ref-Platzer-162_28-0)** [Platzer 2004](#CITEREFPlatzer2004), p. 162 28. ^ [^(***a***)](#cite_ref-Platzer-168_29-0) [^(***b***)](#cite_ref-Platzer-168_29-1) [^(***c***)](#cite_ref-Platzer-168_29-2) [Platzer 2004](#CITEREFPlatzer2004), p. 168 29. ^ [^(***a***)](#cite_ref-Platzer-176_30-0) [^(***b***)](#cite_ref-Platzer-176_30-1) [^(***c***)](#cite_ref-Platzer-176_30-2) [^(***d***)](#cite_ref-Platzer-176_30-3) [Platzer 2004](#CITEREFPlatzer2004), p. 176 30. **[^](#cite_ref-Platzer-174_31-0)** [Platzer 2004](#CITEREFPlatzer2004), p. 174 31. ^ [^(***a***)](#cite_ref-hitchthumbmyth_32-0) [^(***b***)](#cite_ref-hitchthumbmyth_32-1) ["Myth's of Human Genetics: Hitchhiker's Thumb"](http://udel.edu/~mcdonald/myththumb.html). Retrieved 7 November 2012. 32. **[^](#cite_ref-33)** ["Thumb, Distal Hyperextensibility of"](https://www.ncbi.nlm.nih.gov/entrez/dispomim.cgi?id=274200). *OMIM*. NCBI. Retrieved 5 February 2010. 33. **[^](#cite_ref-34)** [Slocum & Pratt 1946](#CITEREFSlocumPratt1946), [McBride 1942](#CITEREFMcBride1942), p. 631 34. **[^](#cite_ref-35)** [Napier 1956](#CITEREFNapier1956), pp. 902–913 35. **[^](#cite_ref-PLOS-2010_36-0)** [Almécija, Moyà-Solà & Alba 2010](#CITEREFAlmécijaMoyà-SolàAlba2010) 36. **[^](#cite_ref-37)** [Costello & Fragaszy 1988](#CITEREFCostelloFragaszy1988), pp. 235–245 37. **[^](#cite_ref-38)** [Young 2003](#CITEREFYoung2003), pp. 165–174, [Christel, Kitzel & Niemitz 2004](#CITEREFChristelKitzelNiemitz2004), pp. 165–194, [Byrne & Byrne 1993](#CITEREFByrneByrne1993), p. 241 38. **[^](#cite_ref-39)** Lin, Yun; Sun, Yu (2015). "Robot grasp planning based on demonstrated grasp strategies". *The International Journal of Robotics Research*. **34**: 26–42. [doi](/wiki/Doi_(identifier) "Doi (identifier)"):[10.1177/0278364914555544](https://doi.org/10.1177%2F0278364914555544). [S2CID](/wiki/S2CID_(identifier) "S2CID (identifier)") [10178250](https://api.semanticscholar.org/CorpusID:10178250). 39. **[^](#cite_ref-40)** Bodranghien, Florian; Mahé, Helene; Baude, Benjamin; Manto, Mario U.; Busegnies, Yves; Camut, Stéphane; Habas, Christophe; Marien, Peter; de Marco, Giovanni (2017-05-10). ["The Click Test: A Novel Tool to Quantify the Age-Related Decline of Fast Motor Sequencing of the Thumb"](https://hal.parisnanterre.fr//hal-02310540/file/Bodranghienetal.TheClickTestANovelTooltoQuantifytheAge-RelatedDeclineofFastMotorSequencingoftheThumbCurrentagingscience2017.pdf) (PDF). *Current Aging Science*. **10** (4): 305–318. [doi](/wiki/Doi_(identifier) "Doi (identifier)"):[10.2174/1874609810666170511100318](https://doi.org/10.2174%2F1874609810666170511100318). [ISSN](/wiki/ISSN_(identifier) "ISSN (identifier)") [1874-6128](https://search.worldcat.org/issn/1874-6128). [PMID](/wiki/PMID_(identifier) "PMID (identifier)") [28494715](https://pubmed.ncbi.nlm.nih.gov/28494715). 40. **[^](#cite_ref-Brüser-167_41-0)** [Brunelli 1999](#CITEREFBrunelli1999), p. 167 41. **[^](#cite_ref-Moyà-Solà-1999_42-0)** [Moyà-Solà, Köhler & Rook 1999](#CITEREFMoyà-SolàKöhlerRook1999), pp. 315–6 42. **[^](#cite_ref-43)** [Leakey, Tobias & Napier 1964](#CITEREFLeakeyTobiasNapier1964): "\[In Homo habilis\] the pollex is well developed and fully opposable and the hand is capable not only of a power grip but of, at least, a simple and usually well developed precision grip." 43. **[^](#cite_ref-44)** Diogo, R.; Richmond, B. G.; Wood, B. (2012). "Evolution and homologies of primate and modern human hand and forearm muscles, with notes on thumb movements and tool use". *Journal of Human Evolution*. **63** (1): 64–78. [Bibcode](/wiki/Bibcode_(identifier) "Bibcode (identifier)"):[2012JHumE..63...64D](https://ui.adsabs.harvard.edu/abs/2012JHumE..63...64D). [doi](/wiki/Doi_(identifier) "Doi (identifier)"):[10.1016/j.jhevol.2012.04.001](https://doi.org/10.1016%2Fj.jhevol.2012.04.001). [PMID](/wiki/PMID_(identifier) "PMID (identifier)") [22640954](https://pubmed.ncbi.nlm.nih.gov/22640954). 44. **[^](#cite_ref-45)** [Harcourt-Smith & Aiello 2004](#CITEREFHarcourt-SmithAiello2004) 45. **[^](#cite_ref-46)** ["HACNS1: Gene enhancer in evolution of human opposable thumb"](http://www.sciencecodex.com/gene_enhancer_in_evolution_of_human_opposable_thumb). Science Codex. September 4, 2008. Retrieved December 16, 2009. 1. **[^](#cite_ref-2)** In some countries and cultures, the thumb is considered a finger. Elsewhere, it is considered a 'digit' due to the few features it has in difference with the other four digits, such as the larger gap, missing phalanx and horizontal curling movement. ## References \[[edit](/w/index.php?title=Thumb&action=edit§ion=23 "Edit section: References")\] - Almécija, S.; Moyà-Solà, S.; Alba, D. M. (2010). ["Early Origin for Human-Like Precision Grasping: A Comparative Study of Pollical Distal Phalanges in Fossil Hominins"](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2908684). *PLOS ONE*. **5** (7): e11727. [Bibcode](/wiki/Bibcode_(identifier) "Bibcode (identifier)"):[2010PLoSO...511727A](https://ui.adsabs.harvard.edu/abs/2010PLoSO...511727A). [doi](/wiki/Doi_(identifier) "Doi (identifier)"):[10.1371/journal.pone.0011727](https://doi.org/10.1371%2Fjournal.pone.0011727). [PMC](/wiki/PMC_(identifier) "PMC (identifier)") [2908684](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2908684). [PMID](/wiki/PMID_(identifier) "PMID (identifier)") [20661444](https://pubmed.ncbi.nlm.nih.gov/20661444). - Ankel-Simons, Friderun (2007). "Chapter 8: Postcranial Skeleton". *Primate Anatomy* (3rd ed.). Academic Press. p. 345. [ISBN](/wiki/ISBN_(identifier) "ISBN (identifier)") [978-0-12-372576-9](/wiki/Special:BookSources/978-0-12-372576-9 "Special:BookSources/978-0-12-372576-9"). - Austin, Noelle M. (2005). "Chapter 9: The Wrist and Hand Complex". In Levangie, Pamela K.; Norkin, Cynthia C. (eds.). *Joint Structure and Function: A Comprehensive Analysis* (4th ed.). Philadelphia: F. A. Davis Company. [ISBN](/wiki/ISBN_(identifier) "ISBN (identifier)") [978-0-8036-1191-7](/wiki/Special:BookSources/978-0-8036-1191-7 "Special:BookSources/978-0-8036-1191-7"). - Brown, David P.; Freeman, Eric D.; Cuccurullo, Sara; Freeman, Ted L. (2004). ["Upper Extremities—Hand Region: Range of Motion of the Digits"](https://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=physmedrehab&part=A4492#A4530). In Cuccurullo, Sara (ed.). *Physical Medicine and Rehabilitation Board Review*. Demos Medical Publishing. [ISBN](/wiki/ISBN_(identifier) "ISBN (identifier)") [978-1-888799-45-3](/wiki/Special:BookSources/978-1-888799-45-3 "Special:BookSources/978-1-888799-45-3"). ([NCBI](/wiki/National_Center_for_Biotechnology_Information "National Center for Biotechnology Information")) - Brunelli, Giovanni R. (1999). ["Stability in the first carpometacarpal joint"](https://books.google.com/books?id=-pzGRMvXFzAC&pg=PA167). In Brüser, Peter; Gilbert, Alain (eds.). *Finger bone and joint injuries*. Taylor & Francis. [ISBN](/wiki/ISBN_(identifier) "ISBN (identifier)") [978-1-85317-690-6](/wiki/Special:BookSources/978-1-85317-690-6 "Special:BookSources/978-1-85317-690-6"). - Byrne, R.W.; Byrne, J.M.E. (1993). ["Complex Leaf-Gathering Skills of Mountain Gorillas (Gorilla g. beringei): Variability and Standardization"](https://web.archive.org/web/20090920100630/http://www.st-andrews.ac.uk/~www_sp/people/personal/rwb/publications/1993%20Byrne_Byrne_AJP.pdf) (PDF). *American Journal of Primatology*. **31** (4): 241–261. [doi](/wiki/Doi_(identifier) "Doi (identifier)"):[10.1002/ajp.1350310402](https://doi.org/10.1002%2Fajp.1350310402). [ISSN](/wiki/ISSN_(identifier) "ISSN (identifier)") [0275-2565](https://search.worldcat.org/issn/0275-2565). 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Grip type and hand preference"](http://www3.interscience.wiley.com/cgi-bin/fulltext/110487513/PDFSTART). *American Journal of Primatology*. **15** (3): 235–245. [doi](/wiki/Doi_(identifier) "Doi (identifier)"):[10.1002/ajp.1350150306](https://doi.org/10.1002%2Fajp.1350150306). [PMID](/wiki/PMID_(identifier) "PMID (identifier)") [31968893](https://pubmed.ncbi.nlm.nih.gov/31968893). [S2CID](/wiki/S2CID_(identifier) "S2CID (identifier)") [86556774](https://api.semanticscholar.org/CorpusID:86556774).^(\[*[dead\ link](/wiki/Wikipedia:Link_rot "Wikipedia:Link rot")*‍\]) - de Klerk, W.J.; Forster, C.A.; Sampson, S.D.; Chinsamy, A.; Ross, C.F. (2000). ["A new coelurosaurian dinosaur from the Early Cretaceous of South Africa"](https://wayback.archive-it.org/all/20120130211657/http://rosslab.uchicago.edu/publications/De%20Klerk%20et%20al.%202000.pdf) (PDF). *Journal of Vertebrate Paleontology*. **20** (2): 324–332. 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