Each hand is made up of twenty-seven bones which form the wrist, palm (and back), and fingers. These bones are articularly specialized, allowing a wide range of flexibility and manipulation. Eight of these bones form the compact arrangement of the wrist, or carpus. These carpal bones include the navicular, the lunate, the pisiform, the capitate, the trapezium, the trapezoid, the hamate, and the triquetrum. These carpal bones are arranged generally in two rows, the proximal (nearer the body) and distal (nearer the fingers). The distal carpals articulate with the five metacarpals. The long metacarpals form the broad structure of the hand, as seen in the dorsal or palmate views. These, in turn, articulate with the proximal phalanges (finger bones). The proximal phalanges join with the middle phalanges, which articulate with the end sections of the fingers, called distal phalanges. The thumb is the exception, as it lacks a middle phalanx.
The capitate bone is one of the eight carpal bones which constitute each wrist. This bone is located in the center of the distal row of the carpal bones.
The hamate bone is one of the eight carpal bones which constitute each wrist. The bone is so named because it features a hook-like prominence (hamulus) which articulates with the fourth and fifth metacarpals.
The lunate bone is one of the eight carpal bones which constitute each wrist. The bone, also called semilumar, is so named because its shape resembles a crescent moon.
The navicular bone is one of the eight carpal bones which constitute each wrist (and is also found in the foot). This bone is so named because its shape resembles that of a sailboat.
The pisiform bone is one of the eight carpal bones which constitute each wrist. This bone, also called the lentiform, is so named because its shape resembles a bean or pea. It is located on the ulnar side of the wrist, in the proximal row of carpal bones.
The trapezium bone is one of the eight carpal bones which constitute each wrist. This bone is the first carpal bone (in the distal row) on the thumb side of the hand.
The trapezoid bone is one of the eight carpal bones which constitute each wrist. This bone is in the distal row of the carpals, between the trapezium and the capitate bones.
The triquetrum is one of the eight carpal bones which constitute each wrist. This bone is so named because of its three-corner, or wedge-like, shape.
The hand features five long bones which extend between the carpals of the wrist and the phalanges (finger bones). The metacarpals are numbered beginning with that of the thumb (#1). The head (distal end) of each metacarpal bone is bulbous at the site of articulation with the phalanges, and features small projections or knobs to which the ligaments of the fingers and palm attach.
The bones of the fingers (and toes) are known as phalanges (singular : phalanx). Each finger has three phalanges, with the exception of the thumb, which has only two. The phalanges are referred to by their position with respect to the body when the hand is extended. The joints at the ends of the fingers, because they are the most distant from the body, are the distal phalanges. The next are the middle phalanges (which the thumb does not have). Those articulating with the metacarpals of the hand are the proximal phalanges. The ends of each phalanx are somewhat bulbous at the site of articulation with other bones. These prominences also serve as sites of attachment for phalangeal ligaments.
The hand features a number of ligamentary attachments within it which help facilitate manual flexibility and dexterity. Tendons may be flexor (they contract, causing the hand or fingers to tighten or curl up) or adductor (they contract, causing the hand or fingers to loosen, or straighten out). Therefore, palmar tendons (those on the palm-side of the hand) generally are flexors, while dorsal tendons (on the back of the hand) usually are adductors. Exceptions to this includes the collateral ligaments which help in side-to-side movement of the digits. The palmar surface of the hand is shown here.
The movement of the fingers, or digits, is achieved by flexors and adductors. The flexors, such as the flexor digitorum superficialis and the flexor digitorum profundus (shown in this palmar view), contract to draw the fingers into a curl. Adductors (not shown in the palmar view) are on the backs of the digits and contract to draw the finger out straight. Collateral ligaments pass along the sides of the digits and work in fine-tuning side-to-side flexions.
The metacarpals are connected together, and to the surrounding bones, by a number of metacarpal ligaments. One of these is the interosseous metacarpal ligament, which binds the bases (proximal ends) of the metacarpals tightly together and to the carpals. Another is the deep transverse metacarpal ligaments, which span the heads (distal ends) of the metacarpals, linking the metacarpals together at some distance apart. This arrangement provides the necessary lateral support which keeps the bones of the hand in the appropriate array. Because this is achieved by ligament rather than bone, the hand has some latitude to compress and expand laterally, as well as curve longitudinally.
The ligaments of the digits are encased in fibrous sheaths of ligamentary material. These sheaths allow contraction of the ligaments without incident friction on the nerves and vessels which surround them. Additionally, where these sheaths meet the joints between phalanges, or between a phalanx and a metacarpal, a large joint capsule may be seen. This joint capsule encloses the joint and any ligaments which may be attached to prominences at the bone ends.
The movement of the fingers, or digits, is achieved by flexors and adductors. The flexors, such as the flexor digitorum superficialis and the flexor digitorum profundus (shown in this palmar view), contract to draw the fingers into a curl. Adductors (not shown in the palmar view) are on the backs of the digits and contract to draw the finger out straight.
The palmar ligaments (those on the palmar side of the hand) include
those which connect the radius and ulna to the wrist (carpal) bones, and
those which attach the fingers to the carpals and metacarpals.