Thumb
Thumb | |
---|---|
Infraclavicular lymph nodes[1] | |
Identifiers | |
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
Definition
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:
- Having a skeleton of 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 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 rather than three. However, recently there have been reports that the thumb, like other fingers, has three phalanges, but lacks a metacarpal bone.[2]
- Has greater breadth in the proximalphalanx
- Is attached to such a mobile 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
Humans
Anatomists and other researchers focused on human anatomy have hundreds of definitions of opposition.
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
Primatologists and hand research pioneers
Other primates
- Primates fall into one of six groups:[7]
- Thumbless: colobus
- Nonopposable thumbs: New World monkeys)
- Pseudo-opposable thumbs: all New World monkeys)
- Opposable thumbs: Old World monkeys (Circopithecidae) except colobus, and all great apes
- Opposable with comparatively long thumbs: gibbons (or lesser apes)
- Yet to be classified: other New World monkeys (tamarins, Aotidae: night or owl monkeys, Pitheciidae: titis, sakis and uakaris, Atelidae: howler and woolly monkeys)
- Thumbless:
The spider monkey compensates for being virtually thumbless by using the hairless part of its long, prehensile tail for grabbing objects. In
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
- Giant pandas — five clawed fingers plus an extra-long sesamoid bone beside the true first finger that, though not a true finger, works like an opposable thumb.[10]
- Most rodents have a partly opposable toe on each front paw, letting them grasp.[11]
- In some Notomys and possibly some Gerbillinae.[12]
- The East African maned rat (Lophiomys imhausi), an arboreal, porcupine-like rodent, has four fingers on its hands and feet and a partially opposable thumb.[13]
- In some
Additionally, in many
Marsupials
- In most Trichosurus and 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, 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.[14]
- Koalas 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.[15]
- Opossums 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, the webbed feet of which restrict opposability).[16]
- The mouse-like Dromiciops gliroides, is not closely related to opossums but has paws similar to these animals, each having opposable toes adapted for gripping.[17]
Reptiles
- The front feet of 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.[18]
Dinosaurs
- Dinosaurs belonging to the family of bird-like dinosaur 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.[19]
- The small predatory dinosaur 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.[20]
- coelurosaur with a long, three-fingered hand which included a partially opposable thumb (a "killer claw").[21]
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
- Most birds have at least one opposable toe on the foot, in various configurations, though these are seldom called "thumbs". They are more often known simply as halluxes.
Pterosaurs
- 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]
Amphibians
- Phyllomedusa, a genus of frogs native to South America.[23]
Human anatomy
Skeleton
The skeleton of the thumb consists of the
Muscles
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]
Extrinsic
A ventral forearm muscle, the
Three dorsal forearm muscles act on the thumb:
The
The
The
The tendons of the extensor pollicis longus and extensor pollicis brevis form what is known as the
Intrinsic
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]
Variations
There is a variation of the human thumb where the angle between the first and second (proximal and distal)
It has been suggested that the variation is an autosomal
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).
Grips
One of the earlier significant contributors to the study of hand grips was orthopedic primatologist and paleoanthropologist
- 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).
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 (
The pad-to-pad pinch between the thumb and index finger is made possible because of the human ability to passively hyperextend the
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
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
The evolution of the fully opposable thumb is usually associated with
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.
See also
Notes
- ^ clinicalconsiderations at The Anatomy Lesson by Wesley Norman (Georgetown University)
- ^ 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
- ^ a b van Nierop et al. 2008, p. 34
- ^ Brown et al. 2004
- ^ "Primates FAQ: Do any primates have opposable thumbs?". Wisconsin Regional Primate Research Center. Retrieved 20 November 2010.
- ^ "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.
- ^ Ankel-Simons 2007, p. 345
- ^ a b c Jones & Lederman 2006, Evolutionary Development and Anatomy of the Hand, p. 12
- ^ Franzen et al. 2009, pp. 15–18
- ^ "The Panda's Thumb". Athro. 2000. Retrieved 21 November 2010.
- ISBN 978-0-7614-3073-5.
- ^ Ellerman 1941, p. 2
- ISBN 978-0-7876-7750-3.
- ^ Nowak 1999, p. 89
- ^ McDade 2003, vol 13, p. 44
- ^ McDade 2003, vol 12, p. 250
- ^ McDade 2003, vol 12, p. 274
- ISBN 9780520276055.
- ^ Russell, D. A.; Séguin, R. (1982). "Reconstruction of the small Cretaceous theropod Stenonychosaurus inequalis and a hypothetical dinosauroid". Syllogeus. 37: 1–43.
- ^ Senter 2006
- ^ 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.
- PMID 33848460.
- .
- ^ Austin 2005, p. 339
- ^ "Muscles of the thumb". Eaton hand. Retrieved 11 May 2010.
- ^ Platzer 2004, p. 162
- ^ a b c Platzer 2004, p. 168
- ^ a b c d Platzer 2004, p. 176
- ^ Platzer 2004, p. 174
- ^ a b "Myth's of Human Genetics: Hitchhiker's Thumb". Retrieved 7 November 2012.
- ^ "Thumb, Distal Hyperextensibility of". OMIM. NCBI. Retrieved 5 February 2010.
- ^ Slocum & Pratt 1946, McBride 1942, p. 631
- ^ Napier 1956, pp. 902–913
- ^ Almécija, Moyà-Solà & Alba 2010
- ^ Costello & Fragaszy 1988, pp. 235–245
- ^ Young 2003, pp. 165–174, Christel, Kitzel & Niemitz 2004, pp. 165–194, Byrne & Byrne 1993, p. 241
- S2CID 10178250.
- PMID 28494715.
- ^ Brunelli 1999, p. 167
- ^ Moyà-Solà, Köhler & Rook 1999, pp. 315–6
- ^ 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."
- PMID 22640954.
- ^ Harcourt-Smith & Aiello 2004
- ^ "HACNS1: Gene enhancer in evolution of human opposable thumb". Science Codex. September 4, 2008. Retrieved December 16, 2009.
- ^ 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
- 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". PLOS ONE. 5 (7): e11727. PMID 20661444.
- Ankel-Simons, Friderun (2007). "Chapter 8: Postcranial Skeleton". Primate Anatomy (3rd ed.). Academic Press. p. 345. ISBN 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 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". In Cuccurullo, Sara (ed.). Physical Medicine and Rehabilitation Board Review. Demos Medical Publishing. ISBN 978-1-888799-45-3. (NCBI)
- Brunelli, Giovanni R. (1999). "Stability in the first carpometacarpal joint". In Brüser, Peter; Gilbert, Alain (eds.). Finger bone and joint injuries. Taylor & Francis. ISBN 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" (PDF). American Journal of Primatology. 31 (4): 241–261. S2CID 84429453. Archived from the original(PDF) on September 20, 2009.
- Christel, Marianne I.; Kitzel, Stefanie; S2CID 23567551.
- Costello, Michael B.; Fragaszy, Dorothy M. (March 1988). "Prehension in Cebus and Saimiri: I. Grip type and hand preference". American Journal of Primatology. 15 (3): 235–245. ]
- 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" (PDF). Journal of Vertebrate Paleontology. 20 (2): 324–332. S2CID 128622530. Archived from the original(PDF) on 2012-01-30.
- Diogo, R; Richmond, BG; 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. PMID 22640954.
- Ellerman, John Reeves (1941). The families and genera of living rodents. Vol. II. Family Muridae. London: British Museum (Natural History).
- Franzen, JL; Gingerich, PD; Habersetzer, J; Hurum, JH; von Koenigswald, W; et al. (2009). Hawks, John (ed.). "Complete Primate Skeleton from the Middle Eocene of Messel in Germany: Morphology and Paleobiology". PLOS ONE. 4 (5): e5723. PMID 19492084.
- Harcourt-Smith, W E H; Aiello, L C (May 2004). "Fossils, feet and the evolution of human bipedal locomotion". Journal of Anatomy. 204 (5): 403–16. PMID 15198703.
- Hsu, Ar-Tyan; Meng-Tsu Hu; Fong Ching Su (July 2008). "Effect of Gender, Flexibility and Thumb Type on Thumb Tip Generation". Journal of Biomechanics. 41 (Supplement 1): S148. .
- ISBN 9780195173154.
- S2CID 12836722.[permanent dead link]
- McBride, Earl Duwain (1942). Disability evaluation: principles of treatment of compensable injuries. Lippincott. p. 631.
- McDade, Melissa C. (2003). "Koalas (Phascolartidae)". In Hutchins, Michael; Kleiman, Devra G.; Geist, Valerius; et al. (eds.). Grzimek's animal life encyclopedia: Volumes 12–16, Mammals I–V (2nd ed.). Farmington Hills, MI: Gale Group.
- Moyà-Solà, Salvador; Köhler, Meike; Rook, Lorenzo (January 5, 1999). "Evidence of hominid-like precision grip capability in the hand of the Miocene ape Oreopithecus" (PDF). PNAS. 96 (1): 313–317. PMID 9874815.
- Napier, John Russell (November 1956). "The prehensile movements of the human hand". J Bone Joint Surg Br. 38 (4): 902–913. PMID 13376678.
- Nowak, Ronald M. (1999). Walker's mammals of the world, Volume 2 (6th ed.). JHU Press. ISBN 978-0-8018-5789-8.
- Platzer, Werner (2004). Color Atlas of Human Anatomy, Vol. 1: Locomotor System (5th ed.). Thieme. ISBN 3-13-533305-1.
- Senter, Phil (2006). "Comparison of forelimb function between Deinonychus and Bambiraptor (Theropoda: Dromaeosauridae)". Journal of Vertebrate Paleontology. 26 (4): 897–906. S2CID 85919882.
- Slocum, D.B.; Pratt, D.R. (1946). "Disability Evaluation for the Hand" (PDF). Journal of Bone and Joint Surgery. 28 (3): 491–5. PMID 20992193.[permanent dead link]
- van Nierop, Onno A.; van der Helm, Aadjan; Overbeeke, Kees J.; Djajadiningrat, Tom J.P. (2008). "A natural human hand model" (PDF). Visual Comput. 24 (1): 31–44. .
- Young, Richard W. (January 2003). "Evolution of the human hand: the role of throwing and clubbing". Journal of Anatomy. 202 (1): 165–174. PMID 12587931.