Finger

For other uses, see Finger (disambiguation).

Fingers of the human left hand

A finger is a type of digit, an organ of manipulation and sensation found in the hands of humans and other primates. Normally humans have five digits on each hand^{citation needed} (exceptions are polydactyly, hypodactyly and digit loss). The first digit is the thumb, followed by index finger, middle finger, ring finger, and little finger or pinky. Some other languages use the same generic term for all five digits of a hand.

Linguistically, it appears that the original sense was to include the thumb as a finger: penkwe-ros (also rendered as penqrós) was, in the inferred Proto-Indo-European language, a suffixed form of penkwe (or penqe), "five", which has given rise to many Indo-European-family words (tens of them defined in English dictionaries) that involve or flow from concepts of fiveness.

Chimpanzees have lower limbs that are specialized for manipulation, and (arguably) have fingers on their lower limbs as well. The term 'finger' is not applied to the digits of most other animals, such as canines, felines, or ungulates, none of which can engage in fine manipulation with their forelimbs as a primate can.

Function

Close-up of the left forefinger's distal phalanx

Further information: Hand § Muscles and tendons

Each finger may flex and extend, abduct and adduct, and so also circumduct. Flexion is by far the strongest movement. In humans, there are two large muscles that produce flexion of each finger, and additional muscles that augment the movement. Each finger may move independently of the others, though the muscle bulks that move each finger may be partly blended, and the tendons may be attached to each other by a net of fibrous tissue, preventing completely free movement. This is particularly noticeable when trying to extend the fourth digit (third finger) with the others flexed.

Fingers are usually moved under conscious control. In humans, they are used for grasping, typing, grooming, writing, caressing, and many other activities. They are also used in signaling, as when wearing a wedding ring, finger counting or when communicating in sign language.

Aside from the genitals, the fingertips possess the highest concentration of touch receptors and thermoreceptors among all areas of the human skin, making them extremely sensitive to heat (and cold), pressure, vibration, texture, and moisture. Thus fingers are commonly used as sensory probes to ascertain properties of objects encountered in the world, and so they are prone to injury.

Fingers do not contain muscles other than arrector pili muscles. The muscles that move the finger joints are in the palm and forearm. The long tendons that deliver motion from the forearm muscles may be observed to move under the skin at the wrist and on the back of the hand.

Fingers

Each of the fingers has unique cultural and functional significance. From the thumb on the radial side to the ulnar side of the hand, the fingers are in this order:

thumb index finger, also called 'pointer finger', or 'forefinger' middle finger, the longest ring finger, also known as fourth finger little finger, also known as 'pinky'

Finger ratio

One of the major finger issues in modern science is John T. Manning's digit ratio, sometimes described as finger ratio - which concerns the ratio of the 2nd finger (index finger) and the 4th finger (ring finger). In 2008 John Manning presented an update on his finger ratio research, titled: 'The finger book'.

Anomalies and diseases

A rare anatomical variation affects 1 in 500 humans, in which the individual has more than the usual number of digits; this is known as polydactyly. A human may also be born without one or more fingers, leading to a reduced total number.

Phalanges are commonly fractured. A damaged tendon can cause significant loss of function in fine motor control, such as with a mallet finger.

The fingers are commonly affected by diseases such as rheumatoid arthritis and gout. Diabetics often use the fingers to obtain blood samples for regular blood sugar testing. Raynaud's phenomenon is a neurovascular disorder that affects the fingers.

See also

• Toe
• Palm
• Knuckle
• Digit ratio (relative finger lengths)
• Home row (of keyboards)
• Nail (anatomy)

External links

• Finger Length Predicts Aggression in Men
• Finger Length Predicts SAT Performance