A hand is a
prehensile
Prehensility is the quality of an appendage or organ (anatomy), organ that has Adaptation (biology), adapted for grasping or holding. The word is derived from the Latin term ''prehendere'', meaning "to grasp". The ability to grasp is likely der ...
, multi-
finger
A finger is a limb of the body and a type of digit, an organ of manipulation and sensation found in the hands of most of the Tetrapods, so also with humans and other primates. Most land vertebrates have five fingers ( Pentadactyly). Chambers ...
ed appendage located at the end of the
forearm
The forearm is the region of the upper limb between the elbow and the wrist. The term forearm is used in anatomy to distinguish it from the arm, a word which is most often used to describe the entire appendage of the upper limb, but which in anat ...
or
forelimb
A forelimb or front limb is one of the paired articulated appendages (limbs) attached on the cranial ( anterior) end of a terrestrial tetrapod vertebrate's torso. With reference to quadrupeds, the term foreleg or front leg is often used instead. ...
of
primate
Primates are a diverse order of mammals. They are divided into the strepsirrhines, which include the lemurs, galagos, and lorisids, and the haplorhines, which include the tarsiers and the simians (monkeys and apes, the latter including huma ...
s such as
human
Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, culture, ...
s,
chimpanzee
The chimpanzee (''Pan troglodytes''), also known as simply the chimp, is a species of great ape native to the forest and savannah of tropical Africa. It has four confirmed subspecies and a fifth proposed subspecies. When its close relative th ...
s,
monkey
Monkey is a common name that may refer to most mammals of the infraorder Simiiformes, also known as the simians. Traditionally, all animals in the group now known as simians are counted as monkeys except the apes, which constitutes an incomple ...
s, and
lemurs. A few other
vertebrate
Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, ...
s such as the
koala
The koala or, inaccurately, koala bear (''Phascolarctos cinereus''), is an arboreal herbivorous marsupial native to Australia. It is the only extant representative of the family Phascolarctidae and its closest living relatives are the womb ...
(which has two
opposable thumbs
The thumb is the first digit of the hand, next to the index finger. 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 ...
on each "hand" and fingerprints extremely similar to human
fingerprint
A fingerprint is an impression left by the friction ridges of a human finger. The recovery of partial fingerprints from a crime scene is an important method of forensic science. Moisture and grease on a finger result in fingerprints on surfac ...
s) 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.
Some evolutionary
anatomists use the term ''hand'' to refer to the appendage of digits on the forelimb more generally—for example, in the context of whether the three
digit
Digit may refer to:
Mathematics and science
* Numerical digit, as used in mathematics or computer science
** Hindu-Arabic numerals, the most common modern representation of numerical digits
* Digit (anatomy), the most distal part of a limb, such ...
s of the
bird
Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...
hand involved the same
homologous
Homology may refer to:
Sciences
Biology
*Homology (biology), any characteristic of biological organisms that is derived from a common ancestor
*Sequence homology, biological homology between DNA, RNA, or protein sequences
* Homologous chrom ...
loss of two digits as in the
dinosaur
Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...
hand.
The human hand usually has five digits: four
finger
A finger is a limb of the body and a type of digit, an organ of manipulation and sensation found in the hands of most of the Tetrapods, so also with humans and other primates. Most land vertebrates have five fingers ( Pentadactyly). Chambers ...
s plus one
thumb
The thumb is the first digit of the hand, next to the index finger. 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 ...
;
these are often referred to collectively as five fingers, however, whereby the thumb is included as one of the fingers.
[ It has 27 bones, not including the ]sesamoid bone
In anatomy, a sesamoid bone () is a bone embedded within a tendon or a muscle. Its name is derived from the Arabic word for ' sesame seed', indicating the small size of most sesamoids. Often, these bones form in response to strain, or can be pres ...
, the number of which varies among people, 14 of which are the phalanges
The phalanges (singular: ''phalanx'' ) 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.
...
(proximal
Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position pro ...
, intermediate and distal
Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position pro ...
) of the fingers and thumb. The metacarpal bones
In human anatomy, the metacarpal bones or metacarpus form the intermediate part of the skeletal hand located between the phalanges of the fingers and the carpal bones of the wrist, which forms the connection to the forearm. The metacarpal bones ...
connect the fingers and the carpal bones
The carpal bones are the eight small bones that make up the wrist (or carpus) that connects the hand to the forearm. The term "carpus" is derived from the Latin carpus and the Greek καρπός (karpós), meaning "wrist". In human anatomy, th ...
of the wrist
In human anatomy, the wrist is variously defined as (1) the Carpal bones, carpus or carpal bones, the complex of eight bones forming the proximal skeletal segment of the hand; "The wrist contains eight bones, roughly aligned in two rows, known ...
. Each human hand has five metacarpals[ and eight carpal bones.
Fingers contain some of the densest areas of nerve endings in the body, and are the richest source of ]tactile
Tactile may refer to:
* Tactile, related to the sense of touch
* Haptics (disambiguation)
* Tactile (device), a text-to-braille translation device
See also
* Tangibility, in law
* Somatosensory system, where sensations are processed
* CD96
CD9 ...
feedback. They also have the greatest positioning capability of the body; thus, the sense of touch is intimately associated with hands. Like other paired organs (eyes, feet, legs) each hand is dominantly controlled by the opposing brain hemisphere
The vertebrate cerebrum (brain) is formed by two cerebral hemispheres that are separated by a groove, the longitudinal fissure. The brain can thus be described as being divided into left and right cerebral hemispheres. Each of these hemispheres ...
, so that handedness
In human biology, handedness is an individual's preferential use of one hand, known as the dominant hand, due to it being stronger, faster or more Fine motor skill, dextrous. The other hand, comparatively often the weaker, less dextrous or sim ...
—the preferred hand choice for single-handed activities such as writing with a pencil, reflects individual brain functioning.
Among humans, the hands play an important function in body language
Body language is a type of communication in which physical behaviors, as opposed to words, are used to express or convey information. Such behavior includes facial expressions, body posture, gestures, eye movement, touch and the use of space. Th ...
and sign language
Sign languages (also known as signed languages) are languages that use the visual-manual modality to convey meaning, instead of spoken words. Sign languages are expressed through manual articulation in combination with non-manual markers. Sign l ...
. Likewise, the ten digits of two hands and the twelve phalanges
The phalanges (singular: ''phalanx'' ) 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.
...
of four fingers (touchable by the thumb) have given rise to number systems and calculation techniques.
Structure
Many mammal
Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...
s and other animal
Animals are multicellular, eukaryotic organisms in the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, are Motilit ...
s have grasping appendages similar in form to a hand such as paws, claws, and talons, but these are not scientifically considered to be grasping hands. The scientific use of the term ''hand'' in this sense to distinguish the terminations of the front paws from the hind ones is an example of anthropomorphism
Anthropomorphism is the attribution of human traits, emotions, or intentions to non-human entities. It is considered to be an innate tendency of human psychology.
Personification is the related attribution of human form and characteristics t ...
. The only true grasping hands appear in the mammalian order of primates
Primates are a diverse order of mammals. They are divided into the strepsirrhines, which include the lemurs, galagos, and lorisids, and the haplorhines, which include the tarsiers and the simians (monkeys and apes, the latter including huma ...
. Hands must also have opposable thumb
The thumb is the first digit of the hand, next to the index finger. 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 ...
s, as described later in the text.
The hand is located at the distal end of each arm. Ape
Apes (collectively Hominoidea ) are a clade of Old World simians native to sub-Saharan Africa and Southeast Asia (though they were more widespread in Africa, most of Asia, and as well as Europe in prehistory), which together with its siste ...
s and monkey
Monkey is a common name that may refer to most mammals of the infraorder Simiiformes, also known as the simians. Traditionally, all animals in the group now known as simians are counted as monkeys except the apes, which constitutes an incomple ...
s are sometimes described as having four hands, because the toes are long and the hallux
Toes are the digits (fingers) of the foot of a tetrapod. Animal species such as cats that walk on their toes are described as being '' digitigrade''. Humans, and other animals that walk on the soles of their feet, are described as being '' pl ...
is opposable and looks more like a thumb
The thumb is the first digit of the hand, next to the index finger. 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 ...
, thus enabling the feet to be used as hands.
The word "hand" is sometimes used by evolutionary anatomists to refer to the appendage of digits on the forelimb such as when researching the homology between the three digit
Digit may refer to:
Mathematics and science
* Numerical digit, as used in mathematics or computer science
** Hindu-Arabic numerals, the most common modern representation of numerical digits
* Digit (anatomy), the most distal part of a limb, such ...
s of the bird
Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...
hand and the dinosaur
Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...
hand.
An adult human male's hand weighs about a pound.
Areas
Areas of the human hand include:
* The ''palm'' (Volar), which is the central region of the anterior part of the hand, located superficially to the metacarpus
In human anatomy, the metacarpal bones or metacarpus form the intermediate part of the skeletal hand located between the phalanges of the fingers and the carpal bones of the wrist, which forms the connection to the forearm. The metacarpal bones ...
. The skin in this area contains dermal papillae to increase friction, such as are also present on the fingers and used for fingerprint
A fingerprint is an impression left by the friction ridges of a human finger. The recovery of partial fingerprints from a crime scene is an important method of forensic science. Moisture and grease on a finger result in fingerprints on surfac ...
s.
* The ''opisthenar'' area (dorsal) is the corresponding area on the posterior part of the hand.
* The ''heel of the hand'' is the area anteriorly to the bases of the metacarpal bones, located in the proximal part of the palm. It is the area that sustains most pressure when using the palm of the hand for support, such as in handstand
__NOTOC__
A handstand is the act of supporting the body in a stable, inverted vertical position by balancing on the hands. In a basic handstand, the body is held straight with arms and legs fully extended, with hands spaced approximately shoulder- ...
.
There are five digits attached to the hand, notably with a nail fixed to the end in place of the normal claw. The four finger
A finger is a limb of the body and a type of digit, an organ of manipulation and sensation found in the hands of most of the Tetrapods, so also with humans and other primates. Most land vertebrates have five fingers ( Pentadactyly). Chambers ...
s can be folded over the palm which allows the grasping of objects. Each finger, starting with the one closest to the thumb, has a colloquial name to distinguish it from the others:
* index finger, pointer finger, forefinger, or 2nd digit
* middle finger or long finger or 3rd digit
* ring finger or 4th digit
* little finger, pinky finger, small finger, baby finger, or 5th digit
The thumb
The thumb is the first digit of the hand, next to the index finger. 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 ...
(connected to the first metacarpal bone
The first metacarpal bone or the metacarpal bone of the thumb is the first bone proximal to the thumb. It is connected to the trapezium of the carpus at the first carpometacarpal joint and to the proximal thumb phalanx at the first metacarpophala ...
and trapezium) is located on one of the sides, parallel to the arm. A reliable way of identifying human hands is from the presence of opposable thumbs. Opposable thumbs are identified by the ability to be brought opposite to the fingers, a muscle action known as opposition.
Bones
The skeleton
A skeleton is the structural frame that supports the body of an animal. There are several types of skeletons, including the exoskeleton, which is the stable outer shell of an organism, the endoskeleton, which forms the support structure inside ...
of the human hand consists of 27 bones:[ the eight ]short
Short may refer to:
Places
* Short (crater), a lunar impact crater on the near side of the Moon
* Short, Mississippi, an unincorporated community
* Short, Oklahoma, a census-designated place
People
* Short (surname)
* List of people known as ...
carpal bones
The carpal bones are the eight small bones that make up the wrist (or carpus) that connects the hand to the forearm. The term "carpus" is derived from the Latin carpus and the Greek καρπός (karpós), meaning "wrist". In human anatomy, th ...
of the wrist
In human anatomy, the wrist is variously defined as (1) the Carpal bones, carpus or carpal bones, the complex of eight bones forming the proximal skeletal segment of the hand; "The wrist contains eight bones, roughly aligned in two rows, known ...
are organized into a proximal row ( scaphoid, lunate
Lunate is a crescent or moon-shaped microlith. In the specialized terminology of lithic reduction, a lunate flake is a small, crescent-shaped flake removed from a stone tool during the process of pressure flaking.
In the Natufian period, a lunat ...
, triquetral
The triquetral bone (; also called triquetrum, pyramidal, three-faced, and formerly cuneiform bone) is located in the wrist on the medial side of the proximal row of the carpus between the lunate and pisiform bones. It is on the ulnar side of the ...
and pisiform
The pisiform bone ( or ), also spelled pisiforme (from the Latin ''pisifomis'', pea-shaped), is a small knobbly, sesamoid bone that is found in the wrist. It forms the ulnar border of the carpal tunnel.
Structure
The pisiform is a sesamoid bone, ...
) which articulates with the bones of the forearm, and a distal row ( trapezium, trapezoid
A quadrilateral with at least one pair of parallel sides is called a trapezoid () in American and Canadian English. In British and other forms of English, it is called a trapezium ().
A trapezoid is necessarily a Convex polygon, convex quadri ...
, capitate and hamate), which articulates with the bases of the five metacarpal bones
In human anatomy, the metacarpal bones or metacarpus form the intermediate part of the skeletal hand located between the phalanges of the fingers and the carpal bones of the wrist, which forms the connection to the forearm. The metacarpal bones ...
of the hand. The heads of the metacarpals will each in turn articulate with the bases of the proximal phalanx of the fingers and thumb. These articulations with the fingers are the metacarpophalangeal joints
The metacarpophalangeal joints (MCP) are situated between the metacarpal bones and the proximal phalanges of the fingers. These joints are of the condyloid kind, formed by the reception of the rounded heads of the metacarpal bones into shallow cavi ...
known as the knuckles. At the palmar aspect of the first metacarpophalangeal joints are small, almost spherical bones called the sesamoid bones. The fourteen phalanges make up the fingers and thumb, and are numbered I-V (thumb to little finger) when the hand is viewed from an anatomical position (palm up). The four fingers each consist of three phalanx bones: proximal, middle, and distal. The thumb only consists of a proximal and distal phalanx.[Saladin, Kenneth S. (2007) ''Anatomy & Physiology: The Unity of Form and Function''. New York, NY: McGraw-Hill.] Together with the phalanges of the fingers and thumb these metacarpal bones form five rays or poly-articulated chains.
Because supination
Motion, the process of movement, is described using specific anatomical terms. Motion includes movement of organs, joints, limbs, and specific sections of the body. The terminology used describes this motion according to its direction relative ...
and pronation
Motion, the process of movement, is described using specific anatomical terms. Motion includes movement of organs, joints, limbs, and specific sections of the body. The terminology used describes this motion according to its direction relative ...
(rotation about the axis of the forearm) are added to the two axes of movements of the wrist, the ulna
The ulna (''pl''. ulnae or ulnas) is a long bone found in the forearm that stretches from the elbow to the smallest finger, and when in anatomical position, is found on the medial side of the forearm. That is, the ulna is on the same side of t ...
and radius
In classical geometry, a radius ( : radii) of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length. The name comes from the latin ''radius'', meaning ray but also the ...
are sometimes considered part of the skeleton of the hand.
There are numerous sesamoid bone
In anatomy, a sesamoid bone () is a bone embedded within a tendon or a muscle. Its name is derived from the Arabic word for ' sesame seed', indicating the small size of most sesamoids. Often, these bones form in response to strain, or can be pres ...
s in the hand, small ossified nodes embedded in tendons; the exact number varies between people: whereas a pair of sesamoid bones are found at virtually all thumb metacarpophalangeal joints, sesamoid bones are also common at the interphalangeal joint of the thumb (72.9%) and at the metacarpophalangeal joints of the little finger (82.5%) and the index finger (48%). In rare cases, sesamoid bones have been found in all the metacarpophalangeal joints and all distal interphalangeal joints except that of the long finger.
The articulations are:
* interphalangeal articulations of hand (the hinge joint
A hinge joint (ginglymus or ginglymoid) is a bone joint in which the articular surfaces are molded to each other in such a manner as to permit motion only in one plane. According to one classification system they are said to be uniaxial (having ...
s between the bones of the digits)
*metacarpophalangeal joint
The metacarpophalangeal joints (MCP) are situated between the metacarpal bones and the proximal phalanges of the fingers. These joints are of the condyloid kind, formed by the reception of the rounded heads of the metacarpal bones into shallow cav ...
s (where the digits meet the palm)
* intercarpal articulations (where the palm meets the wrist)
*wrist
In human anatomy, the wrist is variously defined as (1) the Carpal bones, carpus or carpal bones, the complex of eight bones forming the proximal skeletal segment of the hand; "The wrist contains eight bones, roughly aligned in two rows, known ...
(may also be viewed as belonging to the forearm
The forearm is the region of the upper limb between the elbow and the wrist. The term forearm is used in anatomy to distinguish it from the arm, a word which is most often used to describe the entire appendage of the upper limb, but which in anat ...
).
Arches
The fixed and mobile parts of the hand adapt to various everyday tasks by forming bony arches: longitudinal arches (the rays formed by the finger bones and their associated metacarpal bones), transverse arches (formed by the carpal bones and distal ends of the metacarpal bones), and oblique arches (between the thumb and four fingers):
Of the longitudinal arches or rays of the hand, that of the thumb is the most mobile (and the least longitudinal). While the ray formed by the little finger and its associated metacarpal bone still offers some mobility, the remaining rays are firmly rigid. The phalangeal joints of the index finger, however, offer some independence to its finger, due to the arrangement of its flexor and extension tendons.
The carpal bones form two transversal rows, each forming an arch concave on the palmar side. Because the proximal arch simultaneously has to adapt to the articular surface of the radius and to the distal carpal row, it is by necessity flexible. In contrast, the capitate, the "keystone" of the distal arch, moves together with the metacarpal bones and the distal arch is therefore rigid. The stability of these arches is more dependent of the ligaments and capsules of the wrist than of the interlocking shapes of the carpal bones, and the wrist is therefore more stable in flexion than in extension. The distal carpal arch affects the function of the CMC joints and the hands, but not the function of the wrist or the proximal carpal arch. The ligaments that maintain the distal carpal arches are the transverse carpal ligament and the intercarpal ligaments (also oriented transversally). These ligaments also form the carpal tunnel
In the human body, the carpal tunnel or carpal canal is the passageway on the palmar side of the wrist that connects the forearm to the hand.
The tunnel is bounded by the bones of the wrist and flexor retinaculum from connective tissue. Normall ...
and contribute to the deep
Deep or The Deep may refer to:
Places United States
* Deep Creek (Appomattox River tributary), Virginia
* Deep Creek (Great Salt Lake), Idaho and Utah
* Deep Creek (Mahantango Creek tributary), Pennsylvania
* Deep Creek (Mojave River tributary), C ...
and superficial palmar arch
The superficial palmar arch is formed predominantly by the ulnar artery, with a contribution from the superficial palmar branch of the radial artery. However, in some individuals the contribution from the radial artery might be absent, and instea ...
es. Several muscle tendons attaching to the TCL and the distal carpals also contribute to maintaining the carpal arch.
Compared to the carpal arches, the arch formed by the distal ends of the metacarpal bones is flexible due to the mobility of the peripheral metacarpals (thumb and little finger). As these two metacarpals approach each other, the palmar gutter deepens. The central-most metacarpal (middle finger) is the most rigid. It and its two neighbors are tied to the carpus by the interlocking shapes of the metacarpal bones. The thumb metacarpal only articulates with the trapezium and is therefore completely independent, while the fifth metacarpal (little finger) is semi-independent with the fourth metacarpal (ring finger) which forms a transitional element to the fifth metacarpal.
Together with the thumb, the four fingers form four oblique arches, of which the arch of the index finger functionally is the most important, especially for precision grip, while the arch of the little finger contribute an important locking mechanism for power grip. The thumb is undoubtedly the "master digit" of the hand, giving value to all the other fingers. Together with the index and middle finger, it forms the dynamic tridactyl configuration responsible for most grips not requiring force. The ring and little fingers are more static, a reserve ready to interact with the palm when great force is needed.
Muscles
The muscles acting on the hand can be subdivided into two groups: the extrinsic and intrinsic muscle groups. The extrinsic muscle groups are the long flexors and extensors
In anatomy, extension is a movement of a joint that increases the angle between two bones or body surfaces at a joint. Extension usually results in straightening of the bones or body surfaces involved. For example, extension is produced by extendin ...
. They are called extrinsic because the muscle belly is located on the forearm.
Intrinsic
The intrinsic muscle groups are the thenar
The thenar eminence is the mound formed at the base of the thumb on the palm of the hand by the intrinsic group of muscles of the thumb. The skin overlying this region is the area stimulated when trying to elicit a palmomental reflex. The word ...
(thumb) and hypothenar (little finger) muscles; the interosseous muscles ( four dorsally and three volarly) originating between the metacarpal bones; and the lumbrical muscles arising from the deep flexor (and are special because they have no bony origin) to insert on the dorsal extensor hood mechanism.
Extrinsic
The fingers have two long flexors, located on the underside of the forearm. They insert by tendons to the phalanges of the fingers. The deep flexor attaches to the distal phalanx, and the superficial flexor attaches to the middle phalanx. The flexors allow for the actual bending of the fingers. The thumb has one long flexor and a short flexor in the thenar muscle group. The human thumb also has other muscles in the thenar group ( opponens and abductor brevis muscle), moving the thumb in opposition, making grasping possible.
The extensors are located on the back of the forearm and are connected in a more complex way than the flexors to the dorsum of the fingers. The tendons unite with the interosseous and lumbrical muscles to form the extensorhood mechanism. The primary function of the extensors is to straighten out the digits. The thumb has two extensors in the forearm; the tendons of these form the anatomical snuff box
The anatomical snuff box or snuffbox or foveola radialis is a triangular deepening on the radial, dorsal aspect of the hand—at the level of the carpal bones, specifically, the scaphoid and trapezium bones forming the floor. The name originate ...
. Also, the index finger and the little finger have an extra extensor used, for instance, for pointing. The extensors are situated within 6 separate compartments.
The first four compartments are located in the grooves present on the dorsum of inferior side of radius while the 5th compartment is in between radius and ulna. The 6th compartment is in the groove on the dorsum of inferior side of ulna.
Nerve supply
The hand is innervated by the radial, median
In statistics and probability theory, the median is the value separating the higher half from the lower half of a data sample, a population, or a probability distribution. For a data set, it may be thought of as "the middle" value. The basic fe ...
, and ulnar nerve
In human anatomy, the ulnar nerve is a nerve that runs near the ulna bone. The ulnar collateral ligament of elbow joint is in relation with the ulnar nerve. The nerve is the largest in the human body unprotected by muscle or bone, so injury is ...
s.
; Motor
The radial nerve supplies the finger extensors and the thumb abductor, thus the muscles that extends at the wrist and metacarpophalangeal joints (knuckles); and that abducts and extends the thumb.
The median nerve supplies the flexors of the wrist and digits, the abductors and opponens of the thumb, the first and second lumbrical.
The ulnar nerve supplies the remaining intrinsic muscles of the hand.
All muscles of the hand are innervated by the brachial plexus (C5–T1) and can be classified by innervation:[
; Sensory
The radial nerve supplies the skin on the back of the hand from the thumb to the ring finger and the dorsal aspects of the index, middle, and half ring fingers as far as the proximal interphalangeal joints.
The median nerve supplies the palmar side of the thumb, index, middle, and half ring fingers. Dorsal branches innervates the distal phalanges of the index, middle, and half ring fingers.
The ulnar nerve supplies the ulnar third of the hand, both at the palm and the back of the hand, and the little and half ring fingers.]
There is a considerable variation to this general pattern, except for the little finger and volar surface of the index finger. For example, in some individuals, the ulnar nerve supplies the entire ring finger and the ulnar side of the middle finger, whilst, in others, the median nerve supplies the entire ring finger.
Blood supply
The hand is supplied with blood from two arteries, the ulnar artery and the radial artery
In human anatomy, the radial artery is the main artery of the lateral aspect of the forearm.
Structure
The radial artery arises from the bifurcation of the brachial artery in the antecubital fossa. It runs distally on the anterior part of the f ...
. These arteries form three arches over the dorsal and palmar aspects of the hand, the dorsal carpal arch
The dorsal carpal arch (dorsal carpal network, posterior carpal arch) is an anatomical term for the combination ( anastomosis) of dorsal carpal branch of the radial artery and the dorsal carpal branch of the ulnar artery near the back of the wris ...
(across the back of the hand), the deep palmar arch
The deep palmar arch (deep volar arch) is an arterial network found in the palm. It is usually primarily formed from the terminal part of the radial artery. The ulnar artery also contributes through an anastomosis. This is in contrast to the supe ...
, and the superficial palmar arch
The superficial palmar arch is formed predominantly by the ulnar artery, with a contribution from the superficial palmar branch of the radial artery. However, in some individuals the contribution from the radial artery might be absent, and instea ...
. Together these three arches and their anastomoses
An anastomosis (, plural anastomoses) is a connection or opening between two things (especially cavities or passages) that are normally diverging or branching, such as between blood vessels, leaf veins, or streams. Such a connection may be normal ...
provide oxygenated blood to the palm, the fingers, and the thumb.
The hand is drained by the dorsal venous network of the hand with deoxygenated blood leaving the hand via the cephalic vein and the basilic vein
The basilic vein is a large superficial vein of the upper limb that helps drain parts of the hand and forearm. It originates on the medial (ulnar) side of the dorsal venous network of the hand and travels up the base of the forearm, where its co ...
.
Skin
The glabrous (hairless) skin on the front of the hand, the palm, is relatively thick and can be bent along the hand's flexure lines where the skin is tightly bound to the underlying tissue and bones. Compared to the rest of the body's skin, the hands' palms (as well as the soles of the feet
The foot ( : feet) is an anatomical structure found in many vertebrates. It is the terminal portion of a limb which bears weight and allows locomotion. In many animals with feet, the foot is a separate organ at the terminal part of the leg made ...
) are usually lighter—and even much lighter in dark-skinned individuals, compared to the other side of the hand. Indeed, genes specifically expressed in the dermis
The dermis or corium is a layer of skin between the epidermis (with which it makes up the cutis) and subcutaneous tissues, that primarily consists of dense irregular connective tissue and cushions the body from stress and strain. It is divided i ...
of palmoplantar skin inhibit melanin
Melanin (; from el, μέλας, melas, black, dark) is a broad term for a group of natural pigments found in most organisms. Eumelanin is produced through a multistage chemical process known as melanogenesis, where the oxidation of the amino ...
production and thus the ability to tan, and promote the thickening of the stratum lucidum and stratum corneum
The stratum corneum (Latin for 'horny layer') is the outermost layer of the epidermis. The human stratum corneum comprises several levels of flattened corneocytes that are divided into two layers: the ''stratum disjunctum'' and ''stratum compact ...
layers of the epidermis
The epidermis is the outermost of the three layers that comprise the skin, the inner layers being the dermis and hypodermis. The epidermis layer provides a barrier to infection from environmental pathogens and regulates the amount of water rele ...
. All parts of the skin involved in grasping are covered by papillary ridges (fingerprint
A fingerprint is an impression left by the friction ridges of a human finger. The recovery of partial fingerprints from a crime scene is an important method of forensic science. Moisture and grease on a finger result in fingerprints on surfac ...
s) acting as friction pads. In contrast, the hairy skin on the dorsal side is thin, soft, and pliable, so that the skin can recoil when the fingers are stretched. On the dorsal side, the skin can be moved across the hand up to ; an important input the cutaneous mechanoreceptor
A mechanoreceptor, also called mechanoceptor, is a sensory receptor that responds to mechanical pressure or distortion. Mechanoreceptors are innervated by sensory neurons that convert mechanical pressure into electrical signals that, in animals, ...
s.
The web of the hand is a "fold of skin which connects the digits". These webs, located between each set of digits, are known as skin folds
Skin folds or skinfolds are areas of skin that are naturally folded. Many skin folds are distinct, heritable anatomical features, and may be used for identification of animal species, while others are non-specific and may be produced either by ind ...
(interdigital folds or plica interdigitalis). They are defined as "one of the folds of skin, or rudimentary web, between the fingers and toes".
Variation
The ratio of the length of the index finger to the length of the ring finger in adults is affected by the level of exposure to male sex hormones
Sex hormones, also known as sex steroids, gonadocorticoids and gonadal steroids, are steroid hormones that interact with vertebrate steroid hormone receptors. The sex hormones include the androgens, estrogens, and progestogens. Their effects are ...
of the embryo
An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male spe ...
in utero. This digit ratio is below 1 for both sexes but it is lower in males than in females on average.
Clinical significance
A number of genetic disorder
A genetic disorder is a health problem caused by one or more abnormalities in the genome. It can be caused by a mutation in a single gene (monogenic) or multiple genes (polygenic) or by a chromosomal abnormality. Although polygenic disorders ...
s affect the hand. Polydactyly
Polydactyly or polydactylism (), also known as hyperdactyly, is an anomaly in humans and animals resulting in supernumerary fingers and/or toes. Polydactyly is the opposite of oligodactyly (fewer fingers or toes).
Signs and symptoms
In humans ...
is the presence of more than the usual number of fingers. One of the disorders that can cause this is Catel-Manzke syndrome. The fingers may be fused in a disorder known as syndactyly. Or there may be an absence of one or more central fingers—a condition known as ectrodactyly. Additionally, some people are born without one or both hands ( amelia). Hereditary multiple exostoses of the forearm—also known as hereditary multiple osteochondromas—is another cause of hand and forearm deformity in children and adults.
There are several cutaneous conditions that can affect the hand including the nails.
The autoimmune disease
An autoimmune disease is a condition arising from an abnormal immune response to a functioning body part. At least 80 types of autoimmune diseases have been identified, with some evidence suggesting that there may be more than 100 types. Nearly a ...
rheumatoid arthritis
Rheumatoid arthritis (RA) is a long-term autoimmune disorder that primarily affects joints. It typically results in warm, swollen, and painful joints. Pain and stiffness often worsen following rest. Most commonly, the wrist and hands are involv ...
can affect the hand, particularly the joints of the fingers.
Some conditions can be treated by hand surgery
Hand surgery deals with both surgical and non-surgical treatment of conditions and problems that may take place in the hand or upper extremity (commonly from the tip of the hand to the shoulder)Hand surgery is extremely difficult, ranking last o ...
. These include carpal tunnel syndrome
Carpal tunnel syndrome (CTS) is the collection of symptoms and signs associated with median neuropathy at the carpal tunnel. Most CTS is related to idiopathic compression of the median nerve as it travels through the wrist at the carpal tunn ...
, a painful condition of the hand and fingers caused by compression of the median nerve
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.
The median nerve originates from the lateral and medial cords of the brachial plexus, and has contr ...
, and Dupuytren's contracture, a condition in which fingers bend towards the palm and cannot be straightened. Similarly, injury to the ulnar nerve
In human anatomy, the ulnar nerve is a nerve that runs near the ulna bone. The ulnar collateral ligament of elbow joint is in relation with the ulnar nerve. The nerve is the largest in the human body unprotected by muscle or bone, so injury is ...
may result in a condition in which some of the fingers cannot be flexed.
A common fracture
Fracture is the separation of an object or material into two or more pieces under the action of stress. The fracture of a solid usually occurs due to the development of certain displacement discontinuity surfaces within the solid. If a displa ...
of the hand is a scaphoid fracture—a fracture of the scaphoid bone
The scaphoid bone is one of the carpal bones of the wrist. It is situated between the hand and forearm on the thumb side of the wrist (also called the lateral or radial side). It forms the radial border of the carpal tunnel. The scaphoid bone is ...
, one of the carpal bones. This is the commonest carpal bone fracture and can be slow to heal due to a limited blood flow to the bone. There are various types of fracture to the base of the thumb; these are known as Rolando fracture
The Rolando fracture is a type of broken finger involving the base of the thumb.
It is an intra-articular fracture.
It was first described in 1910 by Silvio Rolando.Rolando S. Fracture de la base du premier metacarpien et principalement sur un ...
s, Bennet's fracture
Bennett fracture is a type of partial broken finger involving the base of the thumb, and extends into the carpometacarpal (CMC) joint.
Treatment typically requires surgery.
This intra-articular fracture is the most common type of fracture o ...
, and Gamekeeper's thumb
Gamekeeper's thumb (also known as skier's thumb or UCL tear) is a type of injury to the ulnar collateral ligament (UCL) of the thumb. The UCL may be merely stretched, or it may be torn from its insertion site into the proximal phalanx of the thum ...
. Another common fracture, known as Boxer's fracture
A boxer's fracture is the break of the 5th metacarpal bones of the hand near the knuckle. Occasionally it is used to refer to fractures of the 4th metacarpal as well. Symptoms include pain and a depressed knuckle.
Classically, it occurs after ...
, is to the neck of a metacarpal. One can also have a broken finger
A broken finger or finger fracture is a common type of bone fracture, affecting a finger. Symptoms may include pain, swelling, tenderness, bruising, deformity and reduced ability to move the finger. Although most finger fractures are easy to trea ...
.
Evolution
The prehensile
Prehensility is the quality of an appendage or organ (anatomy), organ that has Adaptation (biology), adapted for grasping or holding. The word is derived from the Latin term ''prehendere'', meaning "to grasp". The ability to grasp is likely der ...
hands and feet of primate
Primates are a diverse order of mammals. They are divided into the strepsirrhines, which include the lemurs, galagos, and lorisids, and the haplorhines, which include the tarsiers and the simians (monkeys and apes, the latter including huma ...
s evolved
Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation t ...
from the mobile hands of semi- arboreal tree shrews that lived about . This development has been accompanied by important changes in the brain and the relocation of the eyes to the front of the face, together allowing the muscle control and stereoscopic vision necessary for controlled grasping. This grasping, also known as power grip, is supplemented by the precision grip between the thumb and the distal finger pads made possible by the opposable thumbs. ''Hominidae
The Hominidae (), whose members are known as the great apes or hominids (), are a taxonomic family of primates that includes eight extant species in four genera: '' Pongo'' (the Bornean, Sumatran and Tapanuli orangutan); ''Gorilla'' (the ea ...
'' (great apes including humans) acquired an erect bipedal posture about , which freed the hands from the task of locomotion and paved the way for the precision and range of motion in human hands. Functional analyses of the features unique to the hand of modern humans have shown that they are consistent with the stresses and requirements associated with the effective use of paleolithic
The Paleolithic or Palaeolithic (), also called the Old Stone Age (from Greek: παλαιός ''palaios'', "old" and λίθος ''lithos'', "stone"), is a period in human prehistory that is distinguished by the original development of stone too ...
stone tools.[ It is possible that the refinement of the bipedal posture in the earliest hominids evolved to facilitate the use of the trunk as leverage in accelerating the hand.][
While the human hand has unique anatomical features, including a longer thumb and fingers that can be controlled individually to a higher degree, the hands of other primates are anatomically similar and the dexterity of the human hand can not be explained solely on anatomical factors. The neural machinery underlying hand movements is a major contributing factor; primates have evolved direct connections between neurons in cortical motor areas and spinal motoneurons, giving the cerebral cortex monosynaptic control over the motoneurons of the hand muscles; placing the hands "closer" to the brain.][ The recent evolution of the human hand is thus a direct result of the development of the ]central nervous system
The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all par ...
, and the hand, therefore, is a direct tool of our consciousness—the main source of differentiated tactile sensations—and a precise working organ enabling gestures—the expressions of our personalities.[
There are nevertheless several primitive features left in the human hand, including ]pentadactyly
In biology, dactyly is the arrangement of digits (fingers and toes) on the hands, feet, or sometimes wings of a tetrapod animal. It comes from the Greek word δακτυλος (''dáktylos'') = "finger".
Sometimes the ending "-dactylia" is used ...
(having five fingers), the hairless skin of the palm and fingers, and the ''os centrale
An accessory bone or supernumerary bone is a bone that is not normally present in the body, but can be found as a variant in a significant number of people. It poses a risk of being misdiagnosed as bone fractures on radiography.
Wrist and hand
...
'' found in human embryos, prosimians, and apes. Furthermore, the precursors of the intrinsic muscles of the hand are present in the earliest fishes, reflecting that the hand evolved from the pectoral fin and thus is much older than the arm in evolutionary terms.
The proportions of the human hand are plesiomorphic
In phylogenetics, a plesiomorphy ("near form") and symplesiomorphy are synonyms for an ancestral character shared by all members of a clade, which does not distinguish the clade from other clades.
Plesiomorphy, symplesiomorphy, apomorphy, and ...
(shared by both ancestors and extant primate species); the elongated thumbs and short hands more closely resemble the hand proportions of Miocene
The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recen ...
apes than those of extant primates.[ Humans did not evolve from knuckle-walking apes,][ and ]chimpanzee
The chimpanzee (''Pan troglodytes''), also known as simply the chimp, is a species of great ape native to the forest and savannah of tropical Africa. It has four confirmed subspecies and a fifth proposed subspecies. When its close relative th ...
s and gorilla
Gorillas are herbivorous, predominantly ground-dwelling great apes that inhabit the tropical forests of equatorial Africa. The genus ''Gorilla'' is divided into two species: the eastern gorilla and the western gorilla, and either four or fi ...
s independently acquired elongated metacarpals as part of their adaptation to their modes of locomotion. Several primitive hand features most likely present in the chimpanzee-human last common ancestor (CHLCA) and absent in modern humans
Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, culture, an ...
are still present in the hands of ''Australopithecus
''Australopithecus'' (, ; ) is a genus of early hominins that existed in Africa during the Late Pliocene and Early Pleistocene. The genus ''Homo'' (which includes modern humans) emerged within ''Australopithecus'', as sister to e.g. ''Australopi ...
'', ''Paranthropus
''Paranthropus'' is a genus of extinct hominin which contains two widely accepted species: ''Paranthropus robustus, P. robustus'' and ''P. boisei''. However, the validity of ''Paranthropus'' is contested, and it is sometimes considered to be sy ...
'', and '' Homo floresiensis''. This suggests that the derived
Derive may refer to:
* Derive (computer algebra system), a commercial system made by Texas Instruments
* ''Dérive'' (magazine), an Austrian science magazine on urbanism
*Dérive, a psychogeographical concept
See also
*
*Derivation (disambiguatio ...
changes in modern humans and Neanderthal
Neanderthals (, also ''Homo neanderthalensis'' and erroneously ''Homo sapiens neanderthalensis''), also written as Neandertals, are an extinct species or subspecies of archaic humans who lived in Eurasia until about 40,000 years ago. While th ...
s did not evolve until or after the appearance of the earliest Acheulian
Acheulean (; also Acheulian and Mode II), from the French ''acheuléen'' after the type site of Saint-Acheul, is an archaeological industry of stone tool manufacture characterized by the distinctive oval and pear-shaped "hand axes" associated ...
stone tools, and that these changes are associated with tool-related tasks beyond those observed in other hominins.[ The thumbs of '' Ardipithecus ramidus'', an early hominin, are almost as robust as in humans, so this may be a primitive trait, while the palms of other extant higher primates are elongated to the extent that some of the thumb's original function has been lost (most notably in highly arboreal primates such as the spider monkey). In humans, the ]big toe
Toes are the digits (fingers) of the foot of a tetrapod. Animal species such as cats that walk on their toes are described as being ''digitigrade''. Humans, and other animals that walk on the soles of their feet, are described as being ''plant ...
is thus more derived than the thumb.
There is a hypothesis suggesting the form of the modern human hand is especially conducive to the formation of a compact fist, presumably for fighting purposes. The fist is compact and thus effective as a weapon. It also provides protection for the fingers.[ However, this is not widely accepted to be one of the primary selective pressures acting on hand morphology throughout human evolution, with tool use and production being thought to be far more influential.][
]
Additional images
File:Blausen 0440 HandBones.png, Illustration of hand and wrist bones
File:Gray219.png, Bones of the left hand. Volar surface.
File:Gray220.png, Bones of the left hand. Dorsal surface.
File:HandAnthropometry.JPG, Static adult human physical characteristics of the hand
File:814 Radiograph of Hand.jpg, X-ray showing joints
File:Hand Bone Anatomy by Jason Christian.webm, Hand bone anatomy
See also
* Dactylonomy
Finger-counting, also known as dactylonomy, is the act of counting using one's fingers. There are multiple different systems used across time and between cultures, though many of these have seen a decline in use because of the spread of Arabic ...
* Dermatoglyphics
* Finger-counting
* Finger tracking
In the field of gesture recognition and image processing, finger tracking is a high-resolution technique developed in 1969 that is employed to know the consecutive position of the fingers of the user and hence represent objects in 3D.
In additio ...
* Handstand
__NOTOC__
A handstand is the act of supporting the body in a stable, inverted vertical position by balancing on the hands. In a basic handstand, the body is held straight with arms and legs fully extended, with hands spaced approximately shoulder- ...
* Hand strength
Hand strength measurements are of interest to study pathology of the hand that involves loss of muscle strength. Examples of these pathologies are carpal tunnel syndrome, nerve injury, tendon injuries of the hand, and neuromuscular disorders.
Ha ...
* Hand walking
* Human skeletal changes due to bipedalism
* Knuckle-walking
* Palmistry—fortune-telling based on lines in hand palms.
* Manus (anatomy)
* Mudra
A mudra (; sa, मुद्रा, , "seal", "mark", or "gesture"; ,) is a symbolic or ritual gesture or pose in Hinduism, Jainism and Buddhism. While some mudras involve the entire body, most are performed with the hands and fingers.
As wel ...
—Hindu term for hand gestures.
References
External links
Hand anatomy (eMedicine)
Film Board of Canada documentary ''Faces of the Hand''
"The Common Hand"
article in the May 2012 ''National Geographic
''National Geographic'' (formerly the ''National Geographic Magazine'', sometimes branded as NAT GEO) is a popular American monthly magazine published by National Geographic Partners. Known for its photojournalism, it is one of the most widely ...
''
{{Authority control
Upper limb anatomy