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A hand is a
prehensile A prehensile tail. Prehensility is the quality of an appendage An appendage (or outgrowth) is an external body part, or natural prolongation, that protrudes from an organism In biology, an organism (from Ancient Greek, Greek: ὀργ ...
, multi-
finger A finger is a limb of the body and a type of digit (anatomy), digit, an organ of wikt:manipulate, manipulation and Wikt:sensation, sensation found in the hands of most of the Tetrapods, so also with humans and other primates. Most land vertebrat ...

finger
ed appendage located at the end of the
forearm The forearm is the region of the upper limb The upper Limb (anatomy), limbs or upper extremities are the forelimbs of an upright posture, upright-postured tetrapod vertebrate, extending from the scapulae and clavicles down to and including the di ...

forearm
or
forelimb A forelimb or front limb is one of the bilateral symmetry, paired joint, articulated appendages (limb (anatomy), limbs) attached on the cranial (anterior (anatomy), anterior) end of a terrestrial animal, terrestrial tetrapod vertebrate's torso. Wi ...
of
primate A primate ( ) (from Latin , from 'prime, first rank') is a eutherian mammal constituting the Taxonomy (biology), taxonomic order (biology), order Primates (). Primates arose 85–55 million years ago first from small Terrestrial animal, ...

primate
s such as
human Humans (''Homo sapiens'') are the most abundant and widespread species In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes ...

human
s,
chimpanzee The chimpanzee (''Pan troglodytes''), also known simply as chimp, is a species of Hominidae, great ape native to the forest and savannah of tropical Africa. It has four confirmed subspecies and a fifth proposed subspecies. The chimpanzee and t ...

chimpanzee
s,
monkey Monkey is a common name that may refer to certain groups or species of simian mammals of infraorder Simiiformes. The term is applied descriptively to groups of primates, such as families of New World monkeys and Old World monkeys. Many monk ...

monkey
s, and
lemur Lemurs ( ) (from Latin ''lemures'' – ghosts or spirits) are wet-nosed primates of the superfamily SUPERFAMILY is a database and search platform of structural and functional annotation for all proteins and genomes. It classifies amino acid s ...

lemur
s. A few other
vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic ma ...
s such as the
koala The koala or, inaccurately, koala bear (''Phascolarctos cinereus''), is an arboreal Arboreal locomotion is the locomotion of animals in trees. In habitats in which trees are present, animals have evolved to move in them. Some animals m ...
(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 i ...
on each "hand" and fingerprints extremely similar to human
fingerprint A fingerprint is an impression left by the friction ridge The dermis or corium is a layer of skin between the epidermis (skin), epidermis (with which it makes up the cutis (anatomy), cutis) and subcutaneous tissues, that primarily consists ...

fingerprint
s) are often described as having "hands" instead of
paw A paw is the soft foot-like part of a mammal Mammals (from Latin language, Latin , 'breast') are a group of vertebrate animals constituting the class (biology), class Mammalia (), and characterized by the presence of mammary glands which i ...
s on their front limbs. The
raccoon The raccoon ( or , ''Procyon lotor''), sometimes called the common raccoon to distinguish it from other species, is a medium-sized mammal Mammals (from Latin language, Latin , 'breast') are a group of vertebrate animals constituting t ...

raccoon
is usually described as having "hands" though opposable thumbs are lacking. Some evolutionary
anatomist Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, mo ...
s 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 ** Arabic numerals, the most common modern representation of numerical digits * Digit (anatomy), one of several most distal parts of a limb ...
s of the
bird Birds are a group of warm-blooded vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With ...

bird
hand involved the same homologous 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 Geological period, period, between 243 and 233.23 annum, million years ago, although the exact origin and timing of the evolution ...

dinosaur
hand. The human hand usually has five digits: four
finger A finger is a limb of the body and a type of digit (anatomy), digit, an organ of wikt:manipulate, manipulation and Wikt:sensation, sensation found in the hands of most of the Tetrapods, so also with humans and other primates. Most land vertebrat ...

finger
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 ...

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 Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any ind ...
, the number of which varies among people, 14 of which are the
phalanges The phalanges (singular: ''phalanx'' ) are digital Digital usually refers to something using digits, particularly binary digits. Technology and computing Hardware *Digital electronics Digital electronics is a field of electronics Elect ...
(
proximal Standard anatomical terms of location deal unambiguously with the anatomy of animals, including humans. Terms used generally derive from Latin or Greek language, Greek roots and used to describe something in its standard anatomical position. This ...
, and
distal Standard anatomical terms of location deal unambiguously with the anatomy of animals, including humans. Terms used generally derive from Latin or Greek language, Greek roots and used to describe something in its standard anatomical position. This ...
) of the fingers and thumb. The
metacarpal bones In human anatomy, the metacarpal bones or metacarpus form the intermediate part of the skeletal The skeleton refers to the frames of support of animal bodies. There are several different skeletal types: the exoskeleton An exoskeleton (from G ...
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 wikt:carpus#Latin, carpus and the Greek language, Greek wikt:καρπός#Ancient Gree ...

carpal bones
of the
wrist In human anatomy The human body is the structure of a human being Humans (''Homo sapiens'') are the most populous and widespread species In biology, a species is the basic unit of biological classification, classification and ...

wrist
. Each human hand has five
metacarpals In human anatomy, the metacarpal bones or metacarpus, form the intermediate part of the skeleton, 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 ...
and eight carpal bones. Fingers contain some of the densest areas of nerve endings in the body, and are the richest source of feedback. They also have the greatest positioning capability of the body; thus, the
sense of touch The somatosensory system is a part of the sensory nervous system The sensory nervous system is a part of the nervous system In Biology, biology, the nervous system is a Complex system, highly complex part of an animal that coordinates it ...
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 h ...
, so that
handedness In human biology Human biology is an interdisciplinary area of academic study that examines humans through the influences and interplay of many diverse fields such as human genetics, genetics, human evolution, evolution, human physiology, physio ...

handedness
—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 nonverbal communication Nonverbal communication (NVC) is the transmission of messages or signals through a nonverbal platform such as eye contact, facial expressions, gestures, Posture (psychology), posture, and bo ...

body language
and
sign language Sign languages (also known as signed languages) are languages that use the visual-manual modality to convey meaning. Sign languages are expressed through manual articulations in combination with non-manual elements. Sign languages are full-fled ...

sign language
. Likewise, the ten digits of two hands and the twelve
phalanges The phalanges (singular: ''phalanx'' ) are digital Digital usually refers to something using digits, particularly binary digits. Technology and computing Hardware *Digital electronics Digital electronics is a field of electronics Elect ...

phalanges
of four fingers (touchable by the thumb) have given rise to number systems and calculation techniques.


Structure

Many
mammal Mammals (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be i ...
s and other
animal Animals (also called Metazoa) are multicellular A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells ...

animal
s have grasping appendages similar in form to a hand such as
paw A paw is the soft foot-like part of a mammal Mammals (from Latin language, Latin , 'breast') are a group of vertebrate animals constituting the class (biology), class Mammalia (), and characterized by the presence of mammary glands which i ...
s,
claw A claw is a curved, pointed appendage found at the end of a toe or finger in most amniote Amniotes (from Greek ἀμνίον ''amnion'', "membrane surrounding the fetus", earlier "bowl in which the blood of sacrificed animals was caught", ...

claw
s, 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 Humans (''Homo sapiens'') are the most populous and widespread species of primates, characterized by bipedality, opposable thumbs, hairlessness, and intelligence allowing the use of culture, l ...
. The only true grasping hands appear in the mammalian order of
primates A primate ( ) (from Latin , from 'prime, first rank') is a eutherian mammal constituting the Taxonomy (biology), taxonomic order (biology), order Primates (). Primates arose 85–55 million years ago first from small Terrestrial animal, ...
. 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 ...

thumb
s, as described later in the text. The hand is located at the distal end of each arm.
Ape Apes (Hominoidea ) are a branch The branches and leaves of a tree. A branch ( or , ) or tree branch (sometimes referred to in botany Botany, also called , plant biology or phytology, is the science of plant life and a branch of bi ...

Ape
s and
monkey Monkey is a common name that may refer to certain groups or species of simian mammals of infraorder Simiiformes. The term is applied descriptively to groups of primates, such as families of New World monkeys and Old World monkeys. Many monk ...

monkey
s are sometimes described as having four hands, because the toes are long and the
hallux Toes are the s (fingers) of the of a . species such as s that walk on their toes are described as being '. s, and other animals that walk on the soles of their feet, are described as being '; ' animals are those that walk on at the tips of th ...

hallux
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 ...

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 ** Arabic numerals, the most common modern representation of numerical digits * Digit (anatomy), one of several most distal parts of a limb ...
s of the
bird Birds are a group of warm-blooded vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With ...

bird
hand and the
dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 annum, million years ago, although the exact origin and timing of the evolution ...

dinosaur
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 The skeleton refers to the frames of support of animal bodies. There are several different skeletal types: the exoskeleton An exoskeleton (from G ...
. The skin in this area contains
dermal papillae The dermis or corium is a layer of skin between the epidermis (skin), epidermis (with which it makes up the cutis (anatomy), cutis) and subcutaneous tissues, that primarily consists of dense irregular connective tissue and cushions the body from s ...
to increase friction, such as are also present on the fingers and used for
fingerprint A fingerprint is an impression left by the friction ridge The dermis or corium is a layer of skin between the epidermis (skin), epidermis (with which it makes up the cutis (anatomy), cutis) and subcutaneous tissues, that primarily consists ...

fingerprint
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 , 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__ Image:AcroDanceHandstand.jpg, An acro dancer pauses in a precision handstand before Hand walking, handwalking across the stage. A handstand is the act of supporting the body in a stable, inverted vertical position by balancing on the hands ...

handstand
. There are five digits attached to the hand, notably with a
nail Nail or Nails may refer to: In biology * Nail (anatomy), toughened protective protein-keratin (known as alpha-keratin, also found in hair) at the end of an animal digit * Nail (beak), a plate of hard horny tissue at the tip of some bird beaks O ...
fixed to the end in place of the normal
claw A claw is a curved, pointed appendage found at the end of a toe or finger in most amniote Amniotes (from Greek ἀμνίον ''amnion'', "membrane surrounding the fetus", earlier "bowl in which the blood of sacrificed animals was caught", ...

claw
. The four
finger A finger is a limb of the body and a type of digit (anatomy), digit, an organ of wikt:manipulate, manipulation and Wikt:sensation, sensation found in the hands of most of the Tetrapods, so also with humans and other primates. Most land vertebrat ...

finger
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 The index finger (also referred to as forefinger, first finger, pointer finger, trigger finger, digitus secundus, digitus II, and many other terms) is the second finger, digit of a human hand. It is located between the thumb and the middle finge ...

index finger
, pointer finger, forefinger, or 2nd digit *
middle finger The middle finger, long finger, or tall finger is the third digit of the human Humans (''Homo sapiens'') are the most populous and widespread species of primates, characterized by bipedality, opposable thumbs, hairlessness, and intelligen ...

middle finger
or long finger or 3rd digit * ring finger or 4th digit *
little finger The little finger, or pinkie, also known as the fifth digit, or pinky finger, is the most Anatomical terms of location#Hands and feet, ulnar and smallest digit of the human hand, and next to the ring finger. Etymology The word "pinkie" is der ...

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 ...

thumb
(connected to the
first metacarpal bone The first metacarpal bone or the metacarpal bone 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 ...
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 a structural frame that supports an animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consu ...

skeleton
of the human hand consists of 27 bones: the eight short
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 wikt:carpus#Latin, carpus and the Greek language, Greek wikt:καρπός#Ancient Gree ...

carpal bones
of the
wrist In human anatomy The human body is the structure of a human being Humans (''Homo sapiens'') are the most populous and widespread species In biology, a species is the basic unit of biological classification, classification and ...

wrist
are organized into a proximal row (
scaphoid The scaphoid bone is one of the carpal 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 wikt:carpus#Latin, carpus and the Greek lang ...

scaphoid
,
lunate Lunate is a crescent or moon-shaped microlith A microlith is a small Rock (geology), stone tool usually made of flint or chert and typically a centimetre or so in length and half a centimetre wide. They were made by humans from around 35,000 to ...

lunate
,
triquetral The triquetral bone (; also called triquetrum, pyramidal, three-faced, and formerly cuneiform bone) is located in the wrist In human anatomy, the wrist is variously defined as (1) the Carpal bones, carpus or carpal bones, the complex of eigh ...
and
pisiform The pisiform bone ( or ), also spelled pisiforme (from the Latin ''pisifomis'', pea-shaped), is a small knobbly, sesamoid bone In anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the struc ...
) which articulates with the bones of the forearm, and a distal row ( trapezium,
trapezoid In Euclidean geometry Euclidean geometry is a mathematical system attributed to Alexandrian Greek mathematics , Greek mathematician Euclid, which he described in his textbook on geometry: the ''Euclid's Elements, Elements''. Euclid's meth ...

trapezoid
,
capitate The capitate bone is found in the center of the carpal bone region, colloquially known as the wrist, which is at the distal end of the radius and ulna bones. It articulates with the third metacarpal bone (the middle finger) and forms the third car ...
and
hamate The hamate bone (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be ...
), 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 The skeleton refers to the frames of support of animal bodies. There are several different skeletal types: the exoskeleton An exoskeleton (from G ...
of the hand. The heads of the metacarpals will each in turn articulate with the bases of the proximal
phalanx The phalanx ( grc, φάλαγξ; plural phalanxes or phalanges, , ) was a rectangular In Euclidean plane geometry, a rectangle is a quadrilateral A quadrilateral is a polygon in Euclidean geometry, Euclidean plane geometry with four Edge ...
of the fingers and thumb. These articulations with the fingers are the
metacarpophalangeal joints The metacarpophalangeal joints (MCP) are situated between the metacarpal In human anatomy, the metacarpal bones or metacarpus, form the intermediate part of the skeleton, skeletal hand located between the phalanges of the fingers and the carpal bone ...
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 Image:Leaving Yongsan Station.jpg, 300px, Motion involves a change in position In physics, motion is the phenomenon in which an object changes its position (mathematics), position over time. Motion is mathematically described in terms o ...
and
pronation Motion Image:Leaving Yongsan Station.jpg, 300px, Motion involves a change in position In physics, motion is the phenomenon in which an object changes its position (mathematics), position over time. Motion is mathematically described in terms o ...
(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 The long bones are those that are longer than they are wide. They are one of five types of bone A bone is a rigid tissue Tissue may refer to: Biology * Tissue (biology), an ensemble of si ...

ulna
and
radius In classical geometry Geometry (from the grc, γεωμετρία; ' "earth", ' "measurement") is, with , one of the oldest branches of . It is concerned with properties of space that are related with distance, shape, size, and relative ...
are sometimes considered part of the skeleton of the hand. There are numerous
sesamoid bone In anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any ind ...
s in the hand, small
ossified 300 px, Bone is broken down by osteoclasts, and rebuilt by osteoblasts, both of which communicate through cytokine ( IGF) signalling.">Insulin-like_growth_factor.html" ;"title="TGF-β, Insulin-like growth factor">IGF) signalling. Ossification ( ...
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 interphalangeal joints of the hand are the hinge joints between the phalanges The phalanges (singular: ''phalanx'' ) are digital bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the vertebrate skelet ...
(the
hinge joint A hinge joint (ginglymus or ginglymoid) is a bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the skeleton in most vertebrate animals. Bones protect the various organs of the body, produce red blood cell, r ...

hinge joint
s between the bones of the digits) *
metacarpophalangeal joint The metacarpophalangeal joints (MCP) are situated between the metacarpal In human anatomy, the metacarpal bones or metacarpus form the intermediate part of the located between the of the fingers and the of the , which forms the connection to t ...
s (where the digits meet the palm) *
intercarpal articulations The intercarpal joints (joints of the carpal bones 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;Behnk ...
(where the palm meets the wrist) *
wrist In human anatomy The human body is the structure of a human being Humans (''Homo sapiens'') are the most populous and widespread species In biology, a species is the basic unit of biological classification, classification and ...

wrist
(may also be viewed as belonging to the
forearm The forearm is the region of the upper limb The upper Limb (anatomy), limbs or upper extremities are the forelimbs of an upright posture, upright-postured tetrapod vertebrate, extending from the scapulae and clavicles down to and including the di ...

forearm
).


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 The flexor retinaculum (transverse carpal ligament, or anterior annular ligament) is a fibrous band on the palmar side of the hand near the wrist. It arches over the carpal bones of the hands, covering them and forming the carpal tunnel In the hum ...
and the intercarpal ligaments (also oriented transversally). These ligaments also form the
carpal tunnel In the human body The human body is the structure of a human being Humans (''Homo sapiens'') are the most abundant and widespread species In biology, a species is the basic unit of biological classification, classification and a ...
and contribute to the
deep Deep or The Deep may refer to: Places United States * Deep Creek (Appomattox River tributary) Deep Creek is a U.S. Geological Survey. National Hydrography Dataset high-resolution flowline dataThe National Map , accessed April 1, 2011 tributary of t ...
and
superficial palmar arch The superficial palmar arch is formed predominantly by the ulnar artery The ulnar artery is the main blood vessel The blood vessels are the components of the circulatory system The circulatory system, also called the cardiovascular s ...
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 and extensors. 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 on the palm of the hand by the of . The skin overlying this region is the area stimulated when trying to elicit a . The word thenar comes . Structure The following three muscles are c ...
(thumb) and
hypothenar The hypothenar muscles are a group of three muscles of the palm Palm most commonly refers to: * Palm of the hand, the central region of the front of the hand and a subdivision of the cubit * Palm trees, of family Arecaceae **List of Arecaceae gene ...
(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 Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, ...
. 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 Radial is a geometric term of location which may refer to: Mathematics and Direction * Vector (geometric), a line * Radius, adjective form of * Radial distance, a directional coordinate in a polar coordinate system * Radial set * A bearing from ...

radial
,
median In statistics Statistics is the discipline that concerns the collection, organization, analysis, interpretation, and presentation of data. In applying statistics to a scientific, industrial, or social problem, it is conventional to begin wi ...

median
, 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 ...

ulnar nerve
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 The brachial plexus is a network () of nerves (formed by the anterior rami The ventral ramus (pl. ''rami'') (Latin for ''branch'') is the anterior division of a spinal nerve. The ventral rami supply the antero-lateral parts of the trunk (anatomy), ...

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 The ulnar artery is the main blood vessel The blood vessels are the components of the circulatory system The circulatory system, also called the cardiovascular system or the vascular system, is an organ system that permits blood to ci ...

ulnar artery
and the
radial artery In human anatomy The human body is the structure of a human being Humans (''Homo sapiens'') are the most populous and widespread species In biology, a species is the basic unit of biological classification, classification and a ...

radial artery
. 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 wrist. ...
(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 In human anatomy The human body is the structure of a human being. It is composed of ...
, and the
superficial palmar arch The superficial palmar arch is formed predominantly by the ulnar artery The ulnar artery is the main blood vessel The blood vessels are the components of the circulatory system The circulatory system, also called the cardiovascular s ...
. 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 vessel The blood vessels are the components of the circulatory ...
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 In human anatomy, the cephalic vein is a superficial vein A superficial vein is a vein that is close to the surface of the body. This differs from deep veins that are far from the surface. Superficial veins are not paired with an artery, un ...
and the
basilic vein The basilic vein is a large superficial vein of the upper limb The upper Limb (anatomy), limbs or upper extremities are the forelimbs of an upright posture, upright-postured tetrapod vertebrate, extending from the scapulae and clavicles down to ...
.


Skin

The
glabrous Glabrousness refers to hairless skin. Glabrousness may also refer to: * Glabrousness (botany), smooth parts of plants * Glabrousness (entomology), parts of insects without hair or scales See also

* {{disambiguation ...
(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 (plural: feet) is an anatomical Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemist ...

feet
) 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 (skin), epidermis (with which it makes up the cutis (anatomy), cutis) and subcutaneous tissues, that primarily consists of dense irregular connective tissue and cushions the body from s ...
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. Melanin is produced through a multistage chemical process known as melanogenesis, where the oxidation of the ami ...

melanin
production and thus the ability to , and promote the thickening of the
stratum lucidum The stratum lucidum (Latin for "clear layer") is a thin, clear layer of dead skin cells in the epidermis named for its translucent appearance under a microscope A microscope (from grc, μικρός ''mikrós'' 'small' and ''skopeîn'' 'to ...
and
stratum corneum The stratum corneum (Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the ...
layers of the
epidermis The epidermis is the outermost of the three layers that comprise the skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate Vertebrates () comprise all species of animal Animals (also calle ...
. All parts of the skin involved in grasping are covered by papillary ridges (
fingerprint A fingerprint is an impression left by the friction ridge The dermis or corium is a layer of skin between the epidermis (skin), epidermis (with which it makes up the cutis (anatomy), cutis) and subcutaneous tissues, that primarily consists ...

fingerprint
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 Sensory neurons, also known as afferent neurons, are neurons in the nervous system In Biology, biology, the nervous system is a Complex system, highly complex part of an ...
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 (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 hormone A steroid hormone is a steroid that acts as a hormone. Steroid hormones can be grouped into two classes: corticosteroids (typically made in the ...
of the
embryo An embryo is the early stage of development of a multicellular organism A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms ar ...

embryo
in utero The uterus (from Latin "uterus", plural ''uteri'') or womb () is a major female hormone-responsive sex organ, secondary sex organ of the reproductive system in humans and most other mammals. Things occurring in the uterus are described with the ...

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 In the fields of molecular biology and genetics, a genome is all genetic information of an organism. It consists of nucleotide sequences of DNA ( ...
s affect the hand.
Polydactyly Polydactyly or polydactylism (), also known as hyperdactyly, is an anomaly in humans and animals resulting in supernumerary body part, supernumerary fingers and/or toes. Polydactyly is the opposite of oligodactyly (fewer fingers or toes). Signs ...

Polydactyly
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 Syndactyly is a condition wherein two or more digits are fused together. It occurs normally in some mammal Mammals (from Latin language, Latin , 'breast') are a group of vertebrate animals constituting the class (biology), class Mammalia (), ...

syndactyly
. Or there may be an absence of one or more central fingers—a condition known as
ectrodactyly Ectrodactyly, split hand, or cleft hand (derived from the Greek ''ektroma'' "abortion" and ''daktylos'' "finger") involves the deficiency or absence of one or more central digits of the hand or foot and is also known as split hand/split foot malfo ...
. Additionally, some people are born without one or both hands ( amelia).
Hereditary multiple exostoses Hereditary multiple osteochondromas (HMO), also known as hereditary multiple exostoses, is a disorder characterized by the development of multiple benign osteocartilaginous masses ( exostoses) in relation to the ends of long bones of the lower lim ...
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 condition A skin condition, also known as cutaneous condition, is any medical condition A disease is a particular abnormal condition that negatively affects the structure or function (biology), function of all or part of an organism, and that is ...
s that can affect the hand including the
nail Nail or Nails may refer to: In biology * Nail (anatomy), toughened protective protein-keratin (known as alpha-keratin, also found in hair) at the end of an animal digit * Nail (beak), a plate of hard horny tissue at the tip of some bird beaks O ...
s. The
autoimmune disease An autoimmune disease is a condition arising from an abnormal immune response An immune response is a reaction which occurs within an organism for the purpose of defending against foreign invaders. These invaders include a wide variety of differe ...

autoimmune disease
rheumatoid arthritis Rheumatoid arthritis (RA) is a long-term autoimmune disorder that primarily affects synovial joint, joints. It typically results in warm, swollen, and painful joints. Pain and stiffness often worsen following rest. Most commonly, the wrist and ...
can affect the hand, particularly the
joint A joint or articulation (or articular surface) is the connection made between bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the skeleton in most vertebrate animals. Bones protect the various organs of th ...

joint
s 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 on ...

hand surgery
. These include
carpal tunnel syndrome Carpal tunnel syndrome (CTS) is a medical condition due to compression of the median nerve The median nerve is a nerve A nerve is an enclosed, cable-like bundle of nerve fibers called axon An axon (from Greek ἄξων ''áxōn'', axis), ...

carpal tunnel syndrome
, a painful condition of the hand and fingers caused by compression of the
median nerve The median nerve is a nerve A nerve is an enclosed, cable-like bundle of fibers (called axon An axon (from Greek ἄξων ''áxōn'', axis), or nerve fiber (or nerve fibre: see American and British English spelling differences#-re, -er, spe ...

median nerve
, and
Dupuytren's contracture Dupuytren's contracture (also called Dupuytren's disease, Morbus Dupuytren, Viking disease, and Celtic hand) is a condition in which one or more fingers become permanently bent in a flexed position. It is named after Guillaume Dupuytren, who fir ...

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 ...

ulnar nerve
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 (physics), stress. The fracture of a solid usually occurs due to the development of certain displacement discontinuity surfaces within the ...
of the hand is a
scaphoid fracture A scaphoid fracture is a bone fracture, break of the scaphoid bone in the wrist. Symptoms generally includes pain at the base of the thumb which is worse with use of the hand. The Anatomical snuff box, anatomic snuffbox is generally tender and swe ...
—a fracture of the
scaphoid bone The scaphoid bone is one of the carpal 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 wikt:carpus#Latin, carpus and the Greek lang ...
, 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 s, Bennet's fracture, and Gamekeeper's thumb. Another common fracture, known as
Boxer's fracture A boxer's fracture is the bone fracture, break of the 5th Metacarpus, 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. Clas ...
, is to the neck of a metacarpal. One can also have a .


Evolution

The
prehensile A prehensile tail. Prehensility is the quality of an appendage An appendage (or outgrowth) is an external body part, or natural prolongation, that protrudes from an organism In biology, an organism (from Ancient Greek, Greek: ὀργ ...
hands and feet of
primate A primate ( ) (from Latin , from 'prime, first rank') is a eutherian mammal constituting the Taxonomy (biology), taxonomic order (biology), order Primates (). Primates arose 85–55 million years ago first from small Terrestrial animal, ...

primate
s
evolved Evolution is change in the heritable Heredity, also called inheritance or biological inheritance, is the passing on of Phenotypic trait, traits from parents to their offspring; either through asexual reproduction or sexual reproduction, ...

evolved
from the mobile hands of semi-
arboreal Arboreal locomotion is the locomotion of animals in trees. In habitats in which trees are present, animals have evolved to move in them. Some animals may scale trees only occasionally, but others are exclusively arboreal. The habitats pose numer ...
tree shrew The treeshrews (or tree shrews or banxrings) are small mammals native to the tropical forests of South and Southeast Asia. They make up the entire Order (biology), order Scandentia, which split into two Family (biology), families: the Tupaiidae ( ...
s 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 Kaiserpanorama consists of a multi-station viewing apparatus and sets of stereo slides. Patented by A. Fuhrmann around 1890. Stereoscopy (also called stereoscopics, or stereo imaging) is a technique for creating or enhancing the illusion ...
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 great apes or hominids (), are a taxonomic family In , family (from la, familia) is a of people related either by (by recognized birth) or (by marriage or other relationship). The purpose ...
'' (great apes including humans) acquired an erect
bipedal Bipedalism is a form of terrestrial locomotion Terrestrial locomotion has evolved Evolution is change in the heritable Heredity, also called inheritance or biological inheritance, is the passing on of Phenotypic trait, traits from ...

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 or Palæolithic (), also called the Old Stone Age (from Greek palaios - old, lithos - stone), is a period in prehistory Prehistory, also known as pre-literary history, is the period of human history ...
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 and spinal
motoneuron A motor neuron (or motoneuron) is a neuron A neuron or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapse SyNAPSE is a DARPA program that aims to develop electronic n ...

motoneuron
s, 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 In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecu ...

central nervous system
, 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 Primitive may refer to: Mathematics * Primitive element (field theory) * Primitive element (finite field) * Primitive cell (crystallography) * Primitive notion, axiomatic systems * Primitive polynomial (disambiguation), one of two concepts * Primit ...
features left in the human hand, including pentadactyly (having five fingers), the hairless skin of the palm and fingers, and the '' os centrale'' 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 File:Cladogram imaginary birds.jpg, Imaginary cladogram. The yellow mask is a plesiomorphy for each living masked species, because it is ancestral. It is also a symplesiomorphy for them. But for the four living species as a whole, it is an apomorph ...

plesiomorphic
(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 Epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; its name comes from the Greek words (', "less") and (', "new") and mean ...
apes than those of extant primates. Humans did not evolve from knuckle-walking apes, and
chimpanzee The chimpanzee (''Pan troglodytes''), also known simply as chimp, is a species of Hominidae, great ape native to the forest and savannah of tropical Africa. It has four confirmed subspecies and a fifth proposed subspecies. The chimpanzee and t ...

chimpanzee
s and
gorilla Gorillas are herbivorous File:Land_Snail_radula_tracks.jpg#, 250px, Tracks made by terrestrial gastropods with their radulas, scraping green algae from a surface inside a greenhouse A herbivore is an animal anatomically and physiologica ...

gorilla
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 Early modern human (EMH) or anatomically modern human (AMH) are terms used to distinguish ''Homo sapiens Humans (''Homo sapiens'') are the most abundant and widespread of , characterized by and large, complex brains. This has enabled ...
are still present in the hands of ''
Australopithecus ''Australopithecus'' (, ; ; singular: australopith) is a genus of early hominins that existed in Africa during the Late Pliocene and Early Pleistocene. The genera ''Homo'' (which includes modern humans), ''Paranthropus'', and ''Kenyanthropus'' ev ...

Australopithecus
'', ''
Paranthropus ''Paranthropus'' is a genus of extinct hominin which contains two widely accepted species: '' P. robustus'' and '' P. boisei''. However, the validity of ''Paranthropus'' is contested, and it is sometimes considered to be synonym (taxonomy), sy ...
'', and ''
Homo floresiensis ''Homo floresiensis'' ("Flores Man"; nicknamed "Hobbit") is a species of small that inhabited the island of , Indonesia, until the arrival of about 50,000 years ago. The remains of an individual who would have stood about in height were dis ...

Homo floresiensis
''. This suggests that the derived changes in modern humans and
Neanderthal Neanderthals (, also Neandertals, ''Homo neanderthalensis'' or ''Homo sapiens neanderthalensis'') are an extinct species In biology Biology is the natural science that studies life and living organisms, including their anatomy, phys ...
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 (Amiens), Saint-Acheul, is an archaeological industry of stone tool manufacture characterized by distinctive oval and pear-shaped "han ...
stone tools, and that these changes are associated with tool-related tasks beyond those observed in other hominins. The thumbs of ''
Ardipithecus ramidus ''Ardipithecus ramidus'' is a species of australopithecine from the Afar region of Early Pliocene Ethiopia 4.4 million years ago (mya). ''A. ramidus'', unlike modern hominids, has adaptations for both walking on two legs (bipedality) and life in ...
'', 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 Spider monkeys are New World monkey New World monkeys are the five families of primate A primate ( ) (from Latin , from 'prime, first rank') is a eutheria Eutheria (; from Greek , 'good, right' and , 'beast'; ) is the clade A cl ...
). In humans, the
big toe Toes are the digits (fingers) of the foot The foot (plural: feet) is an anatomical Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology Biology is the natural science that studies life and living organisms, including ...

big toe
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 *
Dermatoglyphics Dermatoglyphics (from Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following peri ...
*
Finger-counting Finger-counting, also known as dactylonomy, is the act of counting Counting is the process of determining the number of Element (mathematics), elements of a finite set of objects. The traditional way of counting consists of continually increasing ...
*
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 Three-dimensional ...
*
Handstand __NOTOC__ Image:AcroDanceHandstand.jpg, An acro dancer pauses in a precision handstand before Hand walking, handwalking across the stage. A handstand is the act of supporting the body in a stable, inverted vertical position by balancing on the hands ...

Handstand
*
Hand strength A hand is a prehensile, multi- fingered appendage located at the end of the forearm The forearm is the region of the upper limb between the Elbow-joint, elbow and the wrist. The term forearm is used in anatomy to distinguish it from the arm, ...
*
Hand walking Hand walking is an unusual form of gait (human), human locomotion in which a person travels in a vertically inverted orientation with all body weight resting on the hands. It can be executed with legs fully extended or with variations such as stag, ...
*
Human skeletal changes due to bipedalism The evolution of human Humans (''Homo sapiens'') are the most populous and widespread species of primates, characterized by bipedality, opposable thumbs, hairlessness, and intelligence allowing the use of culture, language and tools. They are ...
*
Knuckle-walking Knuckle-walking is a form of quadrupedal The zebra is a quadruped. Quadrupedalism is a form of terrestrial locomotion where a tetrapod Tetrapods (; from Greek 'four' and 'foot') are four-limbed animals constituting the superclass Tetrap ...
*
Palmistry Palmistry, also known as palm reading, chiromancy, or chirology, is the practice of fortune-telling through the study of the palm. The practice is found all over the world, with numerous cultural variations. Those who practice chiromancy are gen ...

Palmistry
– fortune-telling based on lines in hand palms. *
Manus (anatomy) The manus (Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Roman Repub ...
*
Mudra A mudra (; sa, मुद्रा, , "seal", "mark", or "gesture"; ,) is a symbolic or ritual gesture or pose in Hinduism Hinduism () is an Indian religion Indian religions, sometimes also termed Dharmic religions or Indic re ...
– Hindu term for hand gestures.


References


External links


Hand anatomy (eMedicine)Film Board of Canada documentary ''Faces of the Hand''
(Requires
Adobe Flash Adobe Flash is a multimedia software platform A computing platform or digital platform is the environment in which a piece of software Software is a collection of Instruction (computer science), instructions and data (computing), data that ...
)
''The Common Hand''
article in the May 2012 ''
National Geographic ''National Geographic'' (formerly the ''National Geographic Magazine'', sometimes branded as NAT GEO) is an American monthly magazine published by the National Geographic Society The National Geographic Society (NGS), headquartered in Was ...
'' {{Authority control
Upper limb anatomyThis is a subcategory of anatomy, listing articles relevant to the anatomy of the upper limb in humans. :Lower limb anatomy {{Commons category, Upper limb anatomy Limbs (anatomy) Medical Subject Headings, A01.378.800 ...