View source for Phalanx bone

{{Short description|Digital bone in the hands and feet of most vertebrates}}
{{Other uses|Phalanx (disambiguation)}}
{{Redirect|Phalange|the Spanish or general political movement|Falangism|the Lebanese political movement|Phalangism}}
{{technical|date=January 2014}}
{{Infobox bone
| Name          = Phalanx bone
| Latin         = phalanx<br>pl. phalanges
| Image         = Scheme human hand bones-en.svg
| Caption       = Bones of the hand
| Image2        = File:Ospied-en.svg
| Caption2      = Bones of the foot
| Articulations = [[Metacarpophalangeal joint|Metacarpophalangeal]], [[Metatarsophalangeal joint|metatarsophalangeal]], [[interphalangeal articulations of hand|interphalangeal]]
}}
The '''phalanges''' {{IPAc-en|f|@|'|l|ae|n|dZ|i:|z}} ({{singular}}: '''phalanx''' {{IPAc-en|'|f|ae|l|ae|N|k|s}}) are [[digit (anatomy)|digital]] [[bone]]s in the [[hand]]s and [[foot|feet]] of most [[vertebrates]]. In [[primate]]s, the [[Thumb|thumbs]] and [[Hallux|big toes]] have two phalanges while the other [[Digit (anatomy)|digits]] have three phalanges. The phalanges are classed as [[long bones]].

==Structure==
[[File:Hand-bones.jpg|thumbnail|The phalanges in a human hand]]
{{Image frame|content=
<gallery mode=packed heights=200>
File:Phalanges of left foot - animation01.gif
File:Phalanges of left foot - animation02.gif
</gallery>
Toe bones or phalanges of the foot. Note the big toe has no middle phalanx. {{break}}People vary; sometimes the smallest toe also has none (not shown).<ref name="eval&manage">{{cite journal |last1=Hatch |first1=RL |last2=Hacking |first2=S |title=Evaluation and management of toe fractures. |journal=American Family Physician |date=15 December 2003 |volume=68 |issue=12 |pages=2413–8 |pmid=14705761 |url=https://www.aafp.org/afp/2003/1215/p2413.html}}</ref>
{{legend|red|[[Distal phalanges]] of the foot}}
{{legend|yellow|[[Middle phalanges]] of the foot}}
{{legend|lime|[[Proximal phalanges]] of the foot}}
|border=no|align=}}

The phalanges are the bones that make up the fingers of the hand and the toes of the foot. There are 56 phalanges in the human body, with fourteen on each hand and foot. Three phalanges are present on each finger and toe, with the exception of the [[thumb]] and [[hallux|big toe]], which possess only two. The middle and far phalanges of the {{citation needed span|fourth and|date=November 2021}} fifth toes are often fused together (symphalangism).<ref name="eval&manage"/><ref>{{cite journal |last1=Moulton |first1=Lawrence Stephen |last2=Prasad |first2=Seema |last3=Lamb |first3=Robert G. |last4=Sirikonda |first4=Siva P. |title=How many joints does the 5th toe have? A review of 606 patients of 655 foot radiographs |journal=Foot and Ankle Surgery|date=December 2012 |volume=18 |issue=4 |pages=263–265 |doi=10.1016/j.fas.2012.04.003 |pmid=23093121 |url=https://pubmed.ncbi.nlm.nih.gov/23093121/ |issn=1460-9584}}</ref> The phalanges of the [[hand]] are commonly known as the finger bones. The phalanges of the foot differ from the hand in that they are often shorter and more compressed, especially in the proximal phalanges, those closest to the torso.<ref name=White2011>{{Cite book|last1=White|first1=Tim|last2=Black|first2=Michael|last3=Folkens|first3=Pieter|url=https://www.elsevier.com/books/human-osteology/white/978-0-08-092085-6|title=Human Osteology|publisher=[[Academic Press]]|year=2011|isbn=978-0-080-92085-6|edition=3|page=292|language=en|chapter=13 - Foot: Tarsals, Metatarsals, and Phalanges}}</ref>

A phalanx is named according to whether it is [[Anatomical terms of location#Proximal|proximal]], middle, or [[anatomical terms of location#distal|distal]] and its associated finger or toe. The proximal phalanges are those that are closest to the hand or foot. In the hand, the prominent, knobby ends of the phalanges are known as [[knuckle]]s. The proximal phalanges join with the [[metacarpal]]s of the hand or [[metatarsal]]s of the foot at the [[metacarpophalangeal joint]] or [[metatarsophalangeal joint]]. The intermediate phalanx is not only intermediate in location, but usually also in size. The thumb and large toe do not possess a middle phalanx. The distal phalanges are the bones at the tips of the fingers or toes. The proximal, intermediate, and distal phalanges articulate with one another through [[interphalangeal joints of hand]] and [[interphalangeal joints of the foot]].<ref name=GRAYS2005>{{cite book |last1=Drake |first1=Richard L. |last2=Vogl |first2=Wayne |last3=Tibbitts |first3=Adam W. M. |others=Illustrations by Richard Mitchell and Paul Richardson |year=2005 |title=Gray's Anatomy for Students |publisher=Elsevier/Churchill Livingstone |location=Philadelphia |isbn=978-0-8089-2306-0}}</ref>{{rp|708–711}}{{rp|708–711}}

===Bone anatomy===
Each phalanx consists of a central part, called the ''body'', and two extremities.<ref name=Rollins2022>{{Cite book|last1=Rollins|first1=Jeannean|last2=Long|first2=Bruce|last3=Curtis|first3=Tammy|url=https://www.elsevier.com/books/merrill%27s-atlas-of-radiographic-positioning-and-procedures---3-volume-set/rollins/978-0-323-83279-3|title=Merrill's Atlas of Radiographic Positioning and Procedures - 3-Volume Set|publisher=[[Mosby (imprint)|Mosby]]|year=2022|isbn=978-0-323-83323-3|edition=15|page=147|language=en}}</ref>
* The ''body'' is flat on either side, concave on the palmar surface, and convex on the dorsal surface.<ref name=Singh2014>{{Cite book|last=Singh|first=Vishram|title=Textbook of Anatomy Upper Limb and Thorax; Volume 1|publisher=[[Elsevier Health Sciences]]|year=2014|isbn=978-8-131-23625-3|edition=2|page=32|language=en}}</ref> Its sides are marked with rough areas giving attachment to fibrous sheaths of flexor tendons. It tapers from above downwards.<ref name=Gray's2008>{{Cite book|last=Gray|first=Henry|url=https://www.abebooks.com/Grays-Anatomy-Carter-Henry-Arcturus-Publishing/31017006929/bd|title=Gray's Anatomy|publisher=Arcturus Publishing|year=2008|isbn=978-1-841-93958-2|pages=192–193|language=en}}</ref>
* The ''proximal extremities'' of the bones of the first row present oval, concave articular surfaces, broader from side to side than from front to back. The proximal extremity of each of the bones of the second and third rows presents a double concavity separated by a median ridge.<ref name=Gray's2008/>
* The ''distal extremities'' are smaller than the proximal, and each ends in two [[Condyle (anatomy)|condyles]] (knuckles) separated by a shallow groove; the articular surface extends farther on the palmar than on the dorsal surface, a condition best marked in the bones of the first row.<ref name=Gray's2008/>

In the foot, the proximal phalanges have a body that is compressed from side to side, convex above, and concave below. The base is concave, and the head presents a trochlear surface for articulation with the second phalanx.<ref name=Palastanga2013>{{Cite book|last1=Palastanga|first1=Nigel|last2=Field|first2=Derek |last3=Soames|first3=Roger|title=Anatomy and Human Movement: Structure and Function|publisher=[[Butterworth-Heinemann]]|year=2013|isbn=978-1-483-19274-1|page=336|language=en}}</ref> The middle are remarkably small and short, but rather broader than the proximal. The distal phalanges, as compared with the distal phalanges of the finger, are smaller and are flattened from above downward; each presents a broad base for articulation with the corresponding bone of the second row, and an expanded distal extremity for the support of the nail and end of the toe.<ref name=Iannotti2013>{{Cite book|last1=Iannotti|first1=Joseph|last2=Parker|first2=Richard|url=https://www.elsevier.com/books/the-netter-collection-of-medical-illustrations-musculoskeletal-system-volume-6-part-ii---spine-and-lower-limb/978-1-4160-6382-7|title=The Netter Collection of Medical Illustrations: Musculoskeletal System, Volume 6, Part II - Spine and Lower Limb|publisher=[[Elsevier Health Sciences]]|year=2013|isbn=978-1-416-06382-7|edition=2|page=206|language=en}}</ref>

====Distal phalanx====
In the hand, the distal phalanges are flat on their palmar surface, small, and with a roughened, elevated surface of horseshoe form on the palmar surface, supporting the finger pulp.<ref name=GRAYS1918>{{cite book |last=Gray |first=Henry |title=Anatomy of the Human Body |year=1918 |url=https://archive.org/details/anatomyofhumanbo1985gray |isbn=0-8121-0644-X |url-access=registration }}</ref>{{rp|6b. 3. The Phalanges of the Hand}} The flat, wide expansions found at the tips of the distal phalanges are called "apical tufts". They support the fingertip pads and nails.<ref name="CARTA">{{cite web |title=Apical Phalangeal Tufts |publisher=Center for Academic Research & Training in Anthropogeny |url=http://carta.anthropogeny.org/moca/topics/apical-phalangeal-tufts |access-date=January 28, 2017 |quote=The tufts support the fleshy volar pad (also known as the distal pulp) on the palmar (volar) surface of the finger, as well as the nail on the dorsal surface.}}</ref> The phalanx of the thumb has a pronounced insertion for the [[Flexor pollicis longus muscle|flexor pollicis longus]] (asymmetric towards the radial side), an ungual fossa, and a pair of unequal ungual spines (the ulnar being more prominent). This asymmetry is necessary to ensure that the thumb pulp is always facing the pulps of the other digits, an osteological configuration which provides the maximum contact surface with held objects.<ref name="PLOS-2010" />

In the foot, the distal phalanges are flat on their dorsal surface. It is largest proximally and tapers to the distal end. The proximal part of the phalanx presents a broad base for articulation with the middle phalanx, and an expanded distal extremity for the support of the nail and end of the toe.<ref name=GRAYS1918 />{{rp|6b. 3. The Phalanges of the Foot}} The phalanx ends in a crescent-shaped rough cap of bone [[epiphysis]]&nbsp;— the apical tuft (or ungual tuberosity/process) which covers a larger portion of the phalanx on the volar side than on the dorsal side. Two lateral ungual spines project proximally from the apical tuft. Near the base of the shaft are two lateral tubercles. Between these a V-shaped ridge extending proximally serves for the insertion of the [[Flexor pollicis longus muscle|flexor pollicis longus]]. Another ridge at the base serves for the insertion of the extensor [[aponeurosis]].<ref name="Shrewsbury-Johnson-1975">{{harvnb|Shrewsbury|Johnson|1975| p=784}}</ref> The flexor insertion is sided by two [[Fossa (anatomy)|fossa]]e&nbsp;— the ungual fossa distally and the proximopalmar fossa proximally.

===Development===
The number of phalanges in animals is often expressed as a "phalangeal formula" that indicates the numbers of phalanges in digits, beginning from the innermost medial or proximal. For example, humans have a 2-3-3-3-3 formula for the [[hand]], meaning that the thumb has two phalanges, whilst the other fingers each have three.

In the distal phalanges of the hand the centres for the bodies appear at the distal extremities of the phalanges, instead of at the middle of the bodies, as in the other phalanges. Moreover, of all the bones of the hand, the distal phalanges are the first to ossify.<ref name=GRAYS1918 />{{rp|6b. 3. The Phalanges of the Hand}}

==Function==
{{expand section|date=January 2014}}
[[File:Distal-phalanges-thumb-index Journal.pone.0011727.g001.png|thumb|Thumb and index finger of right hand during pad-to-pad precision grasping in ulnar view.<ref name="PLOS-2010">{{cite journal |last1=Almécija |first1=Sergio |last2=Moyà-Solà |first2=Salvador |last3=Alba |first3=David M. |last4=Strait |first4=David S. |date=22 July 2010 |title=Early Origin for Human-Like Precision Grasping: A Comparative Study of Pollical Distal Phalanges in Fossil Hominins |journal=PLOS ONE  |doi=10.1371/journal.pone.0011727 |pmid=20661444 |pmc=2908684 |volume=5 |issue=7 |pages=e11727|bibcode=2010PLoSO...511727A |doi-access=free }}</ref>]]

The distal phalanges of [[ungulate]]s carry and shape [[Nail (anatomy)|nails]] and [[claw]]s and these in primates are referred to as the ''[[ungual]] phalanges''.

==History of phalanges==
===Etymology===
The term phalanx or phalanges refers to an [[Phalanx formation|ancient Greek army formation]] in which soldiers stand side by side, several rows deep, like an arrangement of fingers or toes.

===Other animals===
Most land [[mammal]]s including humans have a 2-3-3-3-3 formula in both the [[hand]]s (or [[paw]]s) and [[Foot|feet]]. Primitive [[reptile]]s usually had the formula 2-3-4-4-5, and this pattern, with some modification, remained in many later reptiles and in the [[mammal-like reptile]]s. The phalangeal formula in the [[Flipper (anatomy)|flippers]] of [[cetaceans]] (marine mammals) varies widely due to hyperphalangy (the increase in number of [[phalanx bones]] in the digits). In [[humpback whales]], for example, the phalangeal formula is 0/2/7/7/3; in [[pilot whales]] the formula is 1/10/7/2/1.<ref>Cooper et al, [https://www.researchgate.net/publication/320639177_Review_and_experimental_evaluation_of_the_embryonic_development_and_evolutionary_history_of_flipper_development_and_hyperphalangy_in_dolphins_Cetacea_Mammalia "Review and experimental evaluation of the embryonic development and evolutionary history of flipper development and hyperphalangy in dolphins (Cetacea: Mammalia)"], ''ResearchGate'', doi: 10.1002/dvg.23076. October 2017</ref>

In vertebrates, proximal phalanges have a similar placement in the corresponding limbs, be they [[paw]], [[wing]] or [[fin]]. In many species, they are the longest and thickest phalanx ("finger" bone). The middle phalanx also has a corresponding place in their limbs, whether they be [[paw]], [[wing]], [[hoof]] or [[fin]].

The distal phalanges are cone-shaped in most mammals, including most primates, but relatively wide and flat in humans.

====Primates====
[[File:Distal-phalanges-comparison-Journal.pone.0011727.g002.png|thumb|Morphological comparisons of pollical distal phalanges in African apes, extant humans and selected hominins. Although with several morphological differences, all the features related to refined manipulation in modern humans are already present in the late Miocene [[Orrorin]].<ref name="PLOS-2010" />]]
The morphology of the distal phalanges of human thumbs closely reflects an adaptation for a refined precision grip with pad-to-pad contact. This has traditionally been associated with the advent of stone tool-making. However, the intrinsic hand proportions of [[Australopithecus|australopiths]] and the resemblance between human hands and the short hands of [[Miocene]] apes, suggest that human hand proportions are largely [[plesiomorphic]] (as found in ancestral species)&nbsp;— in contrast to the derived elongated hand pattern and poorly developed thumb musculature of other extant [[hominoid]]s.<ref name="PLOS-2010" /><!-- Abstract and Introduction -->

In [[Neanderthal]]s, the apical tufts were expanded and more robust than in modern and early [[Upper Paleolithic]] humans. A proposal that Neanderthal distal phalanges was an adaptation to colder climate (than in Africa) is not supported by a recent comparison showing that in [[hominin]]s, cold-adapted populations possessed smaller apical tufts than do warm-adapted populations.
<ref name="Mittra">{{cite journal |last1=Mittra |first1=ES |last2=Smith |first2=HF |last3=Lemelin |first3=P |last4=Jungers |first4=WL |date=Dec 2007 |title=Comparative morphometrics of the primate apical tuft. |journal=American Journal of Physical Anthropology |pmid=17657781 |doi=10.1002/ajpa.20687 |volume=134 |issue=4 |pages=449–59}}</ref>

In non-human, living primates the apical tufts vary in size, but they are never larger than in humans. Enlarged apical tufts, to the extent they actually reflect expanded digital pulps, may have played a significant role in enhancing friction between the hand and held objects during [[Neolithic]] toolmaking.<ref name="CARTA" />

Among non-human primates [[phylogenesis]] and style of locomotion appear to play a role in apical tuft size. Suspensory primates and [[New World monkey]]s have the smallest apical tufts, while terrestrial quadrupeds and [[Strepsirrhini|Strepsirrhines]] have the largest.<ref name="Mittra" />
A study of the fingertip morphology of four small-bodied New World monkey species, indicated a correlation between increasing small-branch foraging and reduced flexor and extensor tubercles in distal phalanges and broadened distal parts of distal phalanges, coupled with expanded apical pads and developed epidermal ridges. This suggests that widened distal phalanges were developed in arboreal primates, rather than in quadrupedal terrestrial primates.<ref>{{cite journal |last=Hamrick |first=MW |date=Jun 1998 |title=Functional and adaptive significance of primate pads and claws: evidence from New World anthropoids |journal=American Journal of Physical Anthropology |pmid=9637179 |doi=10.1002/(SICI)1096-8644(199806)106:2<113::AID-AJPA2>3.0.CO;2-R |volume=106 |issue=2 |pages=113–27}}</ref>

==== Cetaceans ====
Whales exhibit hyperphalangy. Hyperphalangy is an increase in the number of phalanges beyond the [[Plesiomorphy and symplesiomorphy|plesiomorphic]] mammal condition of three phalanges-per-digit.<ref name=":5">{{Cite journal|last1=Cooper|first1=Lisa|last2=Sears|first2=Karen|last3=Armfield|first3=Brooke|last4=Kala|first4=Bhavneet|last5=Hubler|first5=Merla|last6=Thewissen|first6=J G M|date=2017-10-01|title=Review and experimental evaluation of the embryonic development and evolutionary history of flipper development and hyperphalangy in dolphins (Cetacea: Mammalia)|url=https://www.researchgate.net/publication/320639177|journal=Genesis|volume=56|issue=1|pages=e23076|doi=10.1002/dvg.23076|pmid=29068152|doi-access=free}}</ref> Hyperphalangy was present among extinct [[Marine reptile|marine reptiles]] -- [[Ichthyosaur|ichthyosaurs]], [[Plesiosauria|plesiosaurs]], and [[Mosasaur|mosasaurs]] -- but not other marine mammals, leaving whales as the only [[Marine mammal|marine mammals]] to develop this characteristic.<ref>{{Cite journal|last1=Fedak|first1=Tim J|last2=Hall|first2=Brian K|date=2004|title=Perspectives on hyperphalangy: patterns and processes|journal=Journal of Anatomy|volume=204|issue=3|pages=151–163|doi=10.1111/j.0021-8782.2004.00278.x|issn=0021-8782|pmc=1571266|pmid=15032905}}</ref> The evolutionary process continued over time, and a very derived form of hyperphalangy, with six or more phalanges per digit, evolved convergently in [[Rorqual|rorqual whales]] and [[Oceanic dolphin|oceanic dolphins]], and was likely associated with another wave of signaling within the interdigital tissues.<ref name=":52">{{Cite journal|last1=Cooper|first1=Lisa|last2=Sears|first2=Karen|last3=Armfield|first3=Brooke|last4=Kala|first4=Bhavneet|last5=Hubler|first5=Merla|last6=Thewissen|first6=J G M|date=2017-10-01|title=Review and experimental evaluation of the embryonic development and evolutionary history of flipper development and hyperphalangy in dolphins (Cetacea: Mammalia)|url=https://www.researchgate.net/publication/320639177|journal=Genesis|volume=56|issue=1|pages=e23076|doi=10.1002/dvg.23076|pmid=29068152|doi-access=free}}</ref>

====Other mammals====
{{image frame|content={{Gallery|mode=packed|width=150|height=150
 |File:Handskelett MK1888.png|Comparison of the phalanges of an orangutan, dog, pig, cow, tapir and horse
 |File:Masai Giraffe right-rear foot.jpg|Distal phalanges of a [[Masai giraffe]]
}}

{{Gallery|mode=packed|width=150|height=150
 |File:MC Drei-Finger-Faultier.jpg|Three-fingered sloth
 |File:Scelidotherium right hand.JPG|Terminal phalanx of a ''[[Scelidotherium]]'' [[ground sloth]]
}}}}
In [[ungulate]]s (hoofed mammals) the forelimb is optimized for speed and endurance by a combination of length of stride and rapid step; the proximal forelimb segments are short with large muscles, while the distal segments are elongated with less musculature. In two of the major groups of ungulates, [[Odd-toed ungulate|odd-toed]] and [[Even-toed ungulate|even-toed]] ungulates, what remain of the "hands"&nbsp;— the [[Metacarpus|metacarpal]] and phalangeal bones&nbsp;— are elongated to the extent that they serve little use beyond locomotion. The [[giraffe]], the largest even-toed ungulate, has large terminal phalanges and fused metacarpal bones able to absorb the stress from running.<ref name="Gough-Palmer">{{cite journal |last1=Gough-Palmer |first1=Antony L. |last2=Maclachlan |first2=Jody |last3=Routh |first3=Andrew |date=March 2008 |title=Paws for Thought: Comparative Radiologic Anatomy of the Mammalian Forelimb |journal=RadioGraphics  |doi=10.1148/rg.282075061 |pmid=18349453 |volume=28 |issue=2 |pages=501–510}}</ref>

The [[sloth]] spends its life hanging upside-down from branches, and has highly specialized third and fourth digits for the purpose. They have short and squat proximal phalanges with much longer terminal phalanges. They have [[vestigial]] second and fifth metacarpals, and their palm extends to the distal [[interphalangeal articulations of hand|interphalangeal joints]]. The arboreal specialization of these terminal phalanges makes it impossible for the sloth to walk on the ground where the animal has to drag its body with its claws.<ref name="Gough-Palmer" />

==Additional images==
<gallery>
File:Q11.jpg|Phalanges.
File:Carpus2.jpg|Phalanges.

File:Unilateral extra phalangeal crease.jpg|Unilateral extra phalangeal crease
File:814 Radiograph of Hand.jpg|Joints of the hand in an X-ray image
File:Finger phalanges movement.png|Movement of the three finger phalanges; Distal, middle and proximal 
</gallery>

==See also==
{{Anatomy-terms}}
* [[Hand]]
* [[Foot]]

==References==
{{Reflist|30em}}

==External links==
{{Commons category|Phalanges}}
*[http://www.medterms.com/script/main/art.asp?articlekey=4866 MedTerms.com Medical Dictionary]

{{Bones of skeleton}}
{{Bones of upper limb}}
{{Authority control}}

[[Category:Long bones]]
[[Category:Vertebrate anatomy]]