Hand
The human hand is one of God's most amazing creations, and allows us to manipulate our environment to an extraordinary degree with fine precision.
Anatomy
The human hand consists of 27 bones - two rows of carpals forming the wrist (consisting of the scaphoid, lunate, triquetral and pisiform proximally, and the trapezoid, trapezium, capitate and hamate distally), followed by five metacarpals forming the palm, and 3 phalanges for each finger (proximal, distal and intermediate) and 2 phalanges for the thumb. These bones provide the attachments for the tendons of the long muscles originating from the humerus and the radius and ulner bones of the forearm, as well as the short muscles of the hand.
The wrist is controlled by 4 muscles - the extensor carpi radialis and ulnaris and flexor carpi radialis and ulnaris. Attached to the carpal bones of the wrist, these muscles allow for flexion, extension, abduction, adduction and circumduction. The fingers and thumb are also largely controlled by muscles arising in the forearm, their tendons passing under retinaculums (stong fibrous bands at joints, forming the carpal tunnel ) at the wrist to prevent them bow stringing during flexion and extension. Small muscles in the hand provide additional mobility to the digits, such as the interossei muscles, located between the metacarpals, which abduct and adduct the fingers, and the various muscles of the thenar eminence which provide the ability to oppose thumb and forefinger.
These muscles are innervated by the ulnar, radial and median nerves.[1]
The Hand Throughout The Animal Kingdom
Structures in the human hand are remarkably similar throughout the mammal kingdom and even birds and reptiles. Most mammals have comparable bones, although significantly distorted (such as in a horse's hoof).[2] Other than humans, the only other species with opposable thumbs are other primates, such as chimpanzees.
The opposable thumb makes it possible to grasp branches and manipulate tools. Although the human hand is not nearly as strong as a that of a chimpanzee, when a person turns his or her hand to a task he or she can build enormous skyscrapers or tiny electronic circuits.
