Last updated
Human left thumb
Sobo 1909 130.png
Bones of the thumb, visible at far left
Artery Princeps pollicis artery
Vein Dorsal venous network of hand
Nerve Dorsal digital nerves of radial nerve, proper palmar digital nerves of median nerve
Lymph Infraclavicular lymph nodes [1]
Latin pollex
digitus I manus
digitus primus manus
MeSH D013933
TA98 A01.1.00.053
TA2 151
FMA 24938
Anatomical terminology

The thumb is the first digit of the hand, next to the index finger. [upper-alpha 1] When a person is standing in the medical anatomical position (where the palm is facing to the front), the thumb is the outermost digit. The Medical Latin English noun for thumb is pollex (compare hallux for big toe), and the corresponding adjective for thumb is pollical.



Thumb and fingers

The English word finger has two senses, 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

Linguistically, it appears that the original sense was the first of these two: *penkwe-ros (also rendered as *penqrós) was, in the inferred Proto-Indo-European language, a suffixed form of *penkwe (or *penqe), which has given rise to many Indo-European-family words (tens of them defined in English dictionaries) that involve, or stem from, concepts of fiveness.

The thumb shares the following with each of the other four fingers:

The thumb contrasts with each of the other four fingers by being the only one that:

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


Anatomists and other researchers focused on human anatomy have hundreds of definitions of opposition. [3] Some anatomists [4] 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 and opponens digiti minimi respectively).

Other researchers use another definition, [3] 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.

Primatologists and hand research pioneers John and Prudence Napier defined opposition as: "A movement by which the pulp surface of the thumb is placed squarely in contact with  or diametrically opposite to  the terminal pads of one or all of the remaining fingers." For this true, pulp-to-pulp opposition to be possible, the thumb must rotate about its long axis (at the carpometacarpal joint). [5] Arguably, this definition was chosen to underline what is unique to the human thumb.

Other primates

A bonobo "fishing" for termites, an example of incomplete/"untrue" opposition BonoboFishing02 cropped.jpeg
A bonobo "fishing" for termites, an example of incomplete/"untrue" opposition

The spider monkey compensates for being virtually thumbless by using the hairless part of its long, prehensile tail for grabbing objects. In apes and Old World monkeys, the thumb can be rotated around its axis, but the extensive area of contact between the pulps of the thumb and index finger is a human characteristic. [8]

Darwinius masillae , an Eocene primate transitional fossil between prosimian and simian, had hands and feet with highly flexible digits featuring opposable thumbs and halluces. [9]

Other placental mammals

Additionally, in many polydactyl cats, both the innermost toe and outermost toe (pinky) may become opposable, allowing the cat to perform more complex tasks.[ citation needed ]


Ailurops ursinus Naemundung 5 North Sulawesi cropped.JPG
Left: Opposable toes of the Sulawesi bear cuscus forelimb
Right: Opposable thumb on rear foot of an opossum



In addition to these, some other dinosaurs may have had partially or completely opposed toes in order to manipulate food and/or grasp prey.


Four types of bird feet
(right foot diagrams) Bird-feets-en.svg
Four types of bird feet
(right foot diagrams)


  • The wukongopterid pterosaur Kunpengopterus bore an opposable first toe on each wing. The presence of opposable thumbs in this taxon is thought to be an arboreal adaptation. [22]


Human anatomy


The skeleton of the thumb consists of the first metacarpal bone which articulates proximally with the carpus at the carpometacarpal joint and distally with the proximal phalanx at the metacarpophalangeal joint. This latter bone articulates with the distal phalanx at the interphalangeal joint. Additionally, there are two sesamoid bones at the metacarpophalangeal joint.


The muscles of the thumb can be compared to guy-wires 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. [24]

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. [25]


Musculus flexor pollicis longus.png
Flexor pollicis longus (left) and deep muscles of dorsal forearm (right)

A ventral forearm muscle, the flexor pollicis longus (FPL) originates on the anterior side of the radius distal to the radial tuberosity and from the interosseous membrane. It passes through the carpal tunnel in a separate 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 of the median nerve (C7-C8) [26] It is a persistence of one of the former contrahentes muscles that pulled the fingers or toes together.

Three dorsal forearm muscles act on the thumb:

The abductor pollicis longus (APL) originates on the dorsal sides of both the 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. 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 (C7-C8). [27]

The extensor pollicis longus (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 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 (C7-C8). [27]

The extensor pollicis brevis (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 (C7-T1). [27]

The tendons of the extensor pollicis longus and extensor pollicis brevis 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).


Thenar (left) and dorsal interossei (right) muscles

There are three thenar muscles:

The abductor pollicis brevis (APB) originates on the scaphoid tubercle and the flexor retinaculum. It inserts to the radial sesamoid bone and the proximal phalanx of the thumb. It is innervated by the median nerve (C8-T1). [28]

The flexor pollicis brevis (FPB) has two heads. The superficial head arises on the flexor retinaculum, while the deep head originates on three carpal bones: the trapezium, trapezoid, and capitate. 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, while the deep head is innervated by the ulnar nerve (C8-T1). [28]

The opponens pollicis 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. [28]

Other muscles involved are:

The adductor pollicis 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 (C8-T1). [28]

The first dorsal interosseous, 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. [29]


Hitchhiker's thumb Hitchhikers thumb.jpg
Hitchhiker's thumb

There is a variation of the human thumb where the angle between the first and second (proximal and distal) phalanges varies between 0° and almost 90° when the thumb is in a thumbs-up gesture. [30]

It has been suggested that the variation is an autosomal recessive trait, called a hitchhiker's thumb, with homozygous carriers having an angle close to 90°. [31] 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 seen in other recessive genetic traits. [30]

Other variations of the thumb include brachydactyly type D (which is a thumb with a congenitally short distal phalanx), a triphalangeal thumb (which is a thumb which has 3 phalanges instead of the usual two), and polysyndactyly (which is a combination of radial polydactyly and syndactyly).


Iverson grip 1950.jpg
Left: In a power grip the object is in contact with the palm.
Right: Cricketer Jack Iverson's "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, who proposed organizing the movements of the hand by their anatomical basis as opposed to work done earlier that had only used arbitrary classification. [32] 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 grips: the precision grip and the power grip. [33] The precision and power grip are defined by the position of the thumb and fingers where:

Thumb and index finger during pad-to-pad precision grasping Distal-phalanges-thumb-index Journal.pone.0011727.g001.png
Thumb and index finger during pad-to-pad precision grasping

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 for example). [35] Nevertheless, precision grips are usually only found in higher apes, and only in degrees significantly more restricted than in humans. [36]

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 of the index finger. Most non-human primates have to flex their long fingers in order for the small thumb to reach them. [8]

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. [8]

In robotics, almost all robotic hands 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. [37] 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. [38]

Human evolution

A primitive autonomization of the first 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. [39]

Opposable thumbs are shared by some primates, including most catarrhines.[ citation needed ] The climbing and suspensory behaviour in orthograde apes, such as chimpanzees, 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 monkeys such as baboons, 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. [40]

The evolution of the fully opposable thumb is usually associated with Homo habilis , a forerunner of Homo sapiens . [41] This, however, is the suggested result of evolution from Homo erectus (around 1 mya) via a series of intermediate anthropoid 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. [42]

However, 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. [43] Walking may have been a by-product of busy hands and not vice versa.

HACNS1 (also known as Human Accelerated Region 2) is a gene enhancer "that may have contributed to the evolution of the uniquely opposable human thumb, and possibly also modifications in the ankle or foot that allow humans to walk on two legs". Evidence to date shows that of the 110,000 gene enhancer sequences identified in the human genome, HACNS1 has undergone the most change during the human evolution since the chimpanzee–human last common ancestor. [44]

See also


  1. clinicalconsiderations at The Anatomy Lesson by Wesley Norman (Georgetown University)
  2. 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.
  3. 1 2 van Nierop et al. 2008 , p. 34
  4. Brown et al. 2004
  5. "Primates FAQ: Do any primates have opposable thumbs?". Wisconsin Regional Primate Research Center. Retrieved 20 November 2010.
  6. "The Thumb is the Hero". 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.
  7. Ankel-Simons 2007 , p. 345
  8. 1 2 3 Jones & Lederman 2006 , Evolutionary Development and Anatomy of the Hand, p. 12
  9. Franzen et al. 2009 , pp. 15–18
  10. "The Panda's Thumb". Athro. 2000. Retrieved 21 November 2010.
  11. Stefoff, Rebecca (2008). The Rodent Order. Marshall Cavendish. pp. 62–63, 71–73. ISBN   978-0-7614-3073-5.
  12. Ellerman 1941 , p. 2
  13. Grzimek, Bernhard (2003). Hutchins, Michael; Kleiman, Devra G.; Geist, Valerius; et al. (eds.). Grzimek's Animal Life Encyclopedia, Vol 16, Mammals V (2nd ed.). Farmington Hills, MI: Gale Group. p. 293. ISBN   978-0-7876-7750-3.
  14. Nowak 1999 , p. 89
  15. McDade 2003 , vol 13, p. 44
  16. McDade 2003 , vol 12, p. 250
  17. McDade 2003 , vol 12, p. 274
  18. 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   9780520276055.
  19. Russell, D. A.; Séguin, R. (1982). "Reconstruction of the small Cretaceous theropod Stenonychosaurus inequalis and a hypothetical dinosauroid". Syllogeus. 37: 1–43.
  20. Senter 2006
  21. de Klerk et al. 2000 , p. 327. The left manus shows that the flexed digit I had the potential to partially oppose digits II and III.
  22. 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". Current Biology . 31 (11): 2429–2436.e7. doi: 10.1016/j.cub.2021.03.030 . PMID   33848460.
  23. Bertoluci, Jaime (18 December 2002). "Pedal luring in the leaf-frog Phyllomedusa burmeisteri (Anura, Hylidae, Phyllomedusinae)". Phyllomedusa: Journal of Herpetology. 1 (2): 93. doi: 10.11606/issn.2316-9079.v1i2p93-95 .
  24. Austin 2005 , p. 339
  25. "Muscles of the thumb". Eaton hand. Retrieved 11 May 2010.
  26. Platzer 2004 , p. 162
  27. 1 2 3 Platzer 2004 , p. 168
  28. 1 2 3 4 Platzer 2004 , p. 176
  29. Platzer 2004 , p. 174
  30. 1 2 "Myth's of Human Genetics: Hitchhiker's Thumb" . Retrieved 7 November 2012.
  31. "Thumb, Distal Hyperextensibility of". OMIM. NCBI. Retrieved 5 February 2010.
  32. Slocum & Pratt 1946, McBride 1942 , p. 631
  33. Napier 1956 , pp. 902–913
  34. Almécija, Moyà-Solà & Alba 2010
  35. Costello & Fragaszy 1988 , pp. 235–245
  36. Young 2003 , pp. 165–174, Christel, Kitzel & Niemitz 2004 , pp. 165–194, Byrne & Byrne 1993 , p. 241
  37. Lin, Yun; Sun, Yu (2015). "Robot grasp planning based on demonstrated grasp strategies". The International Journal of Robotics Research. 34: 26–42. doi:10.1177/0278364914555544. S2CID   10178250.
  38. 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" (PDF). Current Aging Science. 10 (4): 305–318. doi:10.2174/1874609810666170511100318. ISSN   1874-6128. PMID   28494715.
  39. Brunelli 1999 , p. 167
  40. Moyà-Solà, Köhler & Rook 1999 , pp. 315–6
  41. Leakey, Tobias & Napier 1964: "[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."
  42. 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. doi:10.1016/j.jhevol.2012.04.001. PMID   22640954.
  43. Harcourt-Smith & Aiello 2004
  44. "HACNS1: Gene enhancer in evolution of human opposable thumb". Science Codex. September 4, 2008. Retrieved December 16, 2009.
  1. 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.

Related Research Articles

<span class="mw-page-title-main">Finger</span> Organ of manipulation and sensation found in the hands of humans and other primates

A finger is a prominent digit on the forelimbs of most tetrapod vertebrate animals, especially those with prehensile extremities such as humans and other primates. Most tetrapods have five digits (pentadactyly), and short digits are typically referred to as toes, while those that are notably elongated are called fingers. In humans, the fingers are flexibly articulated and opposable, serving as an important organ of tactile sensation and fine movements, which are crucial to the dexterity of the hands and the ability to grasp and manipulate objects.

<span class="mw-page-title-main">Carpal bones</span> Eight small bones that make up the wrist (or carpus) that connects the hand to the forearm

The carpal bones are the eight small bones that make up the wrist (carpus) that connects the hand to the forearm. The term "carpus" and "carpal" is derived from the Latin carpus and the Greek καρπός (karpós), meaning "wrist". In human anatomy, the main role of the carpal bones is to articulate with the radial and ulnar heads to form a highly mobile condyloid joint, to provide attachments for thenar and hypothenar muscles, and to form part of the rigid carpal tunnel which allows the median nerve and tendons of the anterior forearm muscles to be transmitted to the hand and fingers.

<span class="mw-page-title-main">Median nerve</span> Nerve of the upper limb

The median nerve is a nerve in humans and other animals in the upper limb. It is one of the five main nerves originating from the brachial plexus.

<span class="mw-page-title-main">Metacarpal bones</span> Bones of hand

In human anatomy, the metacarpal bones or metacarpus, also known as the "palm bones", are the appendicular bones that form the intermediate part of the hand between the phalanges (fingers) and the carpal bones, which articulate with the forearm. The metacarpal bones are homologous to the metatarsal bones in the foot.

<span class="mw-page-title-main">Upper limb</span> Consists of the arm, forearm, and hand

The upper limbs or upper extremities are the forelimbs of an upright-postured tetrapod vertebrate, extending from the scapulae and clavicles down to and including the digits, including all the musculatures and ligaments involved with the shoulder, elbow, wrist and knuckle joints. In humans, each upper limb is divided into the arm, forearm and hand, and is primarily used for climbing, lifting and manipulating objects.

<span class="mw-page-title-main">Phalanx bone</span> Digital bone in the hands and feet of most vertebrates

The phalanges are digital bones in the hands and feet of most vertebrates. In primates, the thumbs and big toes have two phalanges while the other digits have three phalanges. The phalanges are classed as long bones.

In human anatomy, the extensor pollicis longus muscle (EPL) is a skeletal muscle located dorsally on the forearm. It is much larger than the extensor pollicis brevis, the origin of which it partly covers and acts to stretch the thumb together with this muscle.

<span class="mw-page-title-main">Flexor pollicis brevis muscle</span> Muscle in the thenar compartment

The flexor pollicis brevis is a muscle in the hand that flexes the thumb. It is one of three thenar muscles. It has both a superficial part and a deep part.

The flexor pollicis longus is a muscle in the forearm and hand that flexes the thumb. It lies in the same plane as the flexor digitorum profundus. This muscle is unique to humans, being either rudimentary or absent in other primates. A meta-analysis indicated accessory flexor pollicis longus is present in around 48% of the population.

In human anatomy, the abductor pollicis longus (APL) is one of the extrinsic muscles of the hand. Its major function is to abduct the thumb at the wrist. Its tendon forms the anterior border of the anatomical snuffbox.

<span class="mw-page-title-main">Adductor pollicis muscle</span> Muscle in the thenar compartment

In human anatomy, the adductor pollicis muscle is a muscle in the hand that functions to adduct the thumb. It has two heads: transverse and oblique.

<span class="mw-page-title-main">Palmar interossei muscles</span> Muscles between the metacarpals

In human anatomy, the palmar or volar interossei are four muscles, one on the thumb that is occasionally missing, and three small, unipennate, central muscles in the hand that lie between the metacarpal bones and are attached to the index, ring, and little fingers. They are smaller than the dorsal interossei of the hand.

<span class="mw-page-title-main">Carpometacarpal joint</span>

The carpometacarpal (CMC) joints are five joints in the wrist that articulate the distal row of carpal bones and the proximal bases of the five metacarpal bones.

<span class="mw-page-title-main">Dorsal interossei of the hand</span> Muscles between the metacarpals

In human anatomy, the dorsal interossei (DI) are four muscles in the back of the hand that act to abduct (spread) the index, middle, and ring fingers away from hand's midline and assist in flexion at the metacarpophalangeal joints and extension at the interphalangeal joints of the index, middle and ring fingers.

<span class="mw-page-title-main">Abductor digiti minimi muscle of hand</span> Muscle in the hypothenar compartment

In human anatomy, the abductor digiti minimi is a skeletal muscle situated on the ulnar border of the palm of the hand. It forms the ulnar border of the palm and its spindle-like shape defines the hypothenar eminence of the palm together with the skin, connective tissue, and fat surrounding it. Its main function is to pull the little finger away from the other fingers.

<span class="mw-page-title-main">Muscles of the hand</span> Muscles of the human hand

The muscles of the hand are the skeletal muscles responsible for the movement of the hand and fingers. The muscles of the hand can be subdivided into two groups: the extrinsic and intrinsic muscle groups. The extrinsic muscle groups are the long flexors and extensors. They are called extrinsic because the muscle belly is located on the forearm. The intrinsic group are the smaller muscles located within the hand itself. The muscles of the hand are innervated by the radial, median, and ulnar nerves from the brachial plexus.

<span class="mw-page-title-main">Hand</span> Extremity at the end of an arm or forelimb

A hand is a prehensile, multi-fingered appendage located at the end of the forearm or forelimb of primates such as humans, chimpanzees, monkeys, and lemurs. A few other vertebrates such as the koala are often described as having "hands" instead of paws on their front limbs. The raccoon is usually described as having "hands" though opposable thumbs are lacking.

The contrahentes are muscles widely present in the hands of mammals, including monkeys. They are on the palmar/plantar side. There is one each for digits I, II, IV and V, but not III. They pull the fingers/toes down and together.

<span class="mw-page-title-main">Extrinsic extensor muscles of the hand</span>

The extrinsic extensor muscles of the hand are located in the back of the forearm and have long tendons connecting them to bones in the hand, where they exert their action. Extrinsic denotes their location outside the hand. Extensor denotes their action which is to extend, or open flat, joints in the hand. They include the extensor carpi radialis longus (ECRL), extensor carpi radialis brevis (ECRB), extensor digitorum (ED), extensor digiti minimi (EDM), extensor carpi ulnaris (ECU), abductor pollicis longus (APL), extensor pollicis brevis (EPB), extensor pollicis longus (EPL), and extensor indicis (EI).

<span class="mw-page-title-main">Muscles of the thumb</span>

The muscles of the thumb are nine skeletal muscles located in the hand and forearm. The muscles allow for flexion, extension, adduction, abduction and opposition of the thumb. 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 muscles bellies located in the hand proper.