English dictionaries describe finger as meaning either one of the five digits including the thumb, or one of the four excluding the thumb (in which case they are numbered from 1 to 4 starting with the index finger closest to the thumb). Linguistically, it appears that the original sense was to include the thumb as a finger: *penkwe-rosFact: date=September 2008 (also rendered as *penqrósFact: date=September 2008) was, in the inferred Proto-Indo-European language, a suffixed form of *penkwe (or *penqe), "five", which hasFact: date=September 2008 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

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:

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.