hand hand a hand is a prehensile, multi-fingered appendage located at the end of the forearm or forelimb of primates such as humans, chimpanzees, monkeys, and lemurs. a few other vertebrates such as the koala (which has two opposable thumbs on each "hand" and fingerprints extremely similar to human fingerprints) 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. handthe back (left) and front (right) of the two hands of a male humanx-ray of human handdetailsveindorsal venous network of handnerveulnar, median, radial nervesidentifierslatinmanusmeshd006225ta98a01.1.00.025ta2148fma9712anatomical terminology 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 digits of the bird hand involved the same homologous loss of two digits as in the dinosaur hand. the human hand usually has five digits: four fingers plus one 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, the number of which varies among people, 14 of which are the phalanges (proximal, intermediate and distal) of the fingers and thumb. the metacarpal bones connect the fingers and the carpal bones of the wrist. 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 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, so that 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 and sign language. likewise, the ten digits of two hands and the twelve phalanges of four fingers (touchable by the thumb) have given rise to number systems and calculation techniques. structure many mammals and other animals 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. the only true grasping hands appear in the mammalian order of primates. hands must also have opposable thumbs, as described later in the text. the hand is located at the distal end of each arm. apes and monkeys are sometimes described as having four hands, because the toes are long and the hallux is opposable and looks more like a 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 digits of the bird hand and the dinosaur hand. an adult human male's hand weighs about a pound. areas human hand parts 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. the skin in this area contains dermal papillae to increase friction, such as are also present on the fingers and used for fingerprints. 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. there are five digits attached to the hand, notably with a nail fixed to the end in place of the normal claw. the four fingers 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 (connected to the first metacarpal bone 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 bones of the human hand hand-bone animation (metacarpal movement is exaggerated, other than on the thumb) image showing the carpal bones the skeleton of the human hand consists of 27 bones: the eight short carpal bones of the wrist are organized into a proximal row (scaphoid, lunate, triquetral and pisiform) which articulates with the bones of the forearm, and a distal row (trapezium, trapezoid, capitate and hamate), which articulates with the bases of the five 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 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. together with the phalanges of the fingers and thumb these metacarpal bones form five rays or poly-articulated chains. because supination and pronation (rotation about the axis of the forearm) are added to the two axes of movements of the wrist, the ulna and radius are sometimes considered part of the skeleton of the hand. there are numerous sesamoid bones 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 joints between the bones of the digits) metacarpophalangeal joints (where the digits meet the palm) intercarpal articulations (where the palm meets the wrist) wrist (may also be viewed as belonging to the forearm). arches arches of the handred: one of the oblique archesbrown: one of the longitudinal arches of the digitsdark green: transverse carpal archlight green: transverse metacarpal arch 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 and contribute to the deep and superficial palmar arches. 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.