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.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.
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
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.