finger

A finger, or digit, is one of the five terminal segments of the human hand. Each finger includes a set of phalanges, joints, and soft tissues that enable grasping, manipulation, and touch. The thumb differs from the other fingers in its structure and range of motion; together, the five digits form the hand’s versatile lever.

Skeletal structure: The fingers contain proximal, middle, and distal phalanges. The thumb has two phalanges. The knuckles at the base of each finger are the metacarpophalangeal joints; the joints between the phalanges are the proximal and distal interphalangeal joints.

Movement: Flexion and extension occur at the interphalangeal joints, while the metacarpophalangeal joints allow bending and some sideways movement. The thumb can oppose the other fingers, enabling precision grip.

Soft tissues and innervation: Flexor tendons (deep and superficial) run along the palmar side; extensors run on the dorsal side. Sensation is supplied mainly by the median nerve (thumb to index and middle) and the ulnar nerve (ring to little finger); the radial nerve provides dorsal sensation.

Nails and skin: Each finger bears a nail plate on the dorsal distal phalanx, with a nail bed, cuticle, and surrounding skin that provide protection and sensory input.

Function: Fingers support grasping, pinching, and manipulation. Opposition between the thumb and fingers is key to fine motor skills, while flexible joints allow delicate handling and force generation.

Variations and conditions: Congenital differences include polydactyly (extra fingers) and brachydactyly (short fingers). Syndactyly (fusion of fingers) and traumatic injuries can affect function.

Fingerprints: The volar skin contains friction ridges that form unique patterns used for identification and tactile sensing.