The human hand is a complex structure that represents the most distal part of the upper limb. It is composed of five digits - thumb or pollux, index finger, middle finger, ring finger, and pinkie or little finger. The skeleton of each hand is usually formed by 27 bones, excluding the sesamoid bones.

Overall, the bones of the hand can be categorized into three groups:

Carpal bones (carpals) (Read more!) - eight small irregularly shaped bones that are arranged in two rows; they are the most proximally located bones of the hand;
Metacarpal bones (metacarpals) (Read more!) - five long bones that are all similarly shaped; they link the carpals with the phalanges;
Phalanges (Read more!) - fourteen relatively small bones that form the fingers; they are also called the digital bones; phalanges are the most distally located bones in the hand; each finger has three phalanges (proximal phalanx, intermediate or middle phalanx, and distal phalanx), except the thumb, which is composed of two phalanges.

In addition to these bones, each hand can have several more bones called the accessory or sesamoid bones. They are embedded within the tendons of the hand muscles. The sesamoid bones vary in number and shape in each individual.

A pair of sesamoid bones are usually found on the palmar aspect at the head of the first metacarpal bone. These bones have significant functional implications for the thumb motions. Some other sesamoid bones are commonly found at the second and fifth metacarpophalangeal joints.

The hand connects with the forearm through the radius, ulna, lunate bone, and scaphoid bone at the radiocarpal (wrist) joint. The term wrist is applied to the region formed by all the carpal bones, and it connects to the rest of the hand at the carpometacarpal joints.

Overall, the arrangement of the hand bones forms three arches - one longitudinal and two transverse (proximal and distal). The longitudinal arch spans lengthwise, while the proximal transverse arch is formed at the level of the carpal bones and the distal transverse arch is found at the metacarpal heads.

These arches contribute to the hand's ability to grasp objects. The carpal bone arrangement in the proximal transverse arch forms the floor of the carpal tunnel, protecting and supporting the median nerve and flexor tendons.

Note: Several specific terms are used when describing the hand. The term palmar applies to the grasping side of the hand or the palm, while the word dorsal is used when describing the dorsum of the hand. The little finger side is known as the ulnar or medial side, while the thumb side is the radial or lateral side.

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Bones of hand