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A finger is a prominent digit on the of most tetrapod vertebrate , especially those with prehensile extremities (i.e. ) such as and other . Most tetrapods have five digits (dactyly),Chambers 1998 p. 603Oxford Illustrated pp. 311, 380 and short digits (i.e. significantly shorter than the metacarpal/) are typically referred to as , while those that are notably elongated are called fingers. In humans, the fingers are flexibly joint and opposable, serving as an important organ of somatosensory and fine movements, which are crucial to the dexterity of the hands and the ability to grasp and manipulate objects.
Chimpanzees have that are specialized for manipulation, and (arguably) have fingers (instead of ) on their lower limbs as well. In the case of primates in general, the digits of the hand are overwhelmingly referred to as "fingers"."It is generally accepted that the precision grip and independent finger movements (IFMs) in monkey and man are controlled by the direct (monosynaptic) corticomotoneuronal (CM) pathway." Primate fingers have both fingernails and fingerprints.
Research has been carried out on the embryonic development of domestic fowl showing that an interdigital webbing forms between the tissues that become the toes, which subsequently regresses by apoptosis. If apoptosis fails to occur, the interdigital skin remains intact. Many animals have developed Webbed foot or skin between the fingers from this like the Wallace's flying frog.V. Garcia-Martinez, D. Macias et al: Internucleosomal DNA fragmentation and programmed cell death (apoptosis) in the interdigital tissue of the embryonic chick leg bud. In: Journal of Cell Science. Vol. 6, Issue 1, September 1993, pp. 201-208.M. A. Fernandez-Teran, J. M. Hurle: Syndactyly induced by Janus Green B in the embryonic chick leg bud: a reexamination. In Development, Volume 8, Issue 1, December 1984, pp. 159–175.Sajid Malik: Syndactyly: phenotypes, genetics and current classification. In: European Journal of Human Genetics. Vol. 20, 2012, pp. 817–824.
English dictionaries describe finger as meaning either one of the five digits including the thumb, or one of the four digits excluding the thumb (in which case they are numbered from 1 to 4 starting with the index finger closest to the thumb).Oxford Advanced p. 326
The palm has five bones known as metacarpal bones, one to each of the five digits. Human hands contain fourteen digital bones, also called phalanges, or phalanx bones: two in the thumb (the thumb has no middle phalanx) and three in each of the four fingers. These are the distal phalanx, carrying the nail, the middle phalanx, and the proximal phalanx. Joints are formed wherever two or more of these bones meet. Each of the fingers has three joints:
are small ossified nodes embedded in the tendons to provide extra leverage and reduce pressure on the underlying tissue. Many exist around the palm at the bases of the digits; the exact number varies between different people.
The Joint are: interphalangeal articulations between phalangeal bones, and metacarpophalangeal joints connecting the phalanges to the metacarpal bones.
Fingers do not contain muscles (other than arrector pili). The 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.
Muscles of the fingers can be subdivided into extrinsic and intrinsic muscles. The extrinsic muscles are the long flexors and extensors. They are called extrinsic because the muscle belly is located on the forearm.
The fingers have two long flexors, located on the underside of the forearm. They insert by tendons to the phalanges of the fingers. The deep flexor attaches to the distal phalanx, and the superficial flexor attaches to the middle phalanx. The flexors allow for the actual bending of the fingers. The thumb has one long flexor and a short flexor in the thenar muscle group. The human thumb also has other muscles in the thenar group (opponens and abductor brevis muscle), moving the thumb in opposition, making grasping possible.
The extensors are located on the back of the forearm and are connected in a more complex way than the flexors to the dorsum of the fingers. The tendons unite with the interosseous and lumbrical muscles to form the extensorhood mechanism. The primary function of the extensors is to straighten out the digits. The thumb has two extensors in the forearm; the tendons of these form the anatomical snuff box. Also, the index finger and the little finger have an extra extensor, used for instance for pointing. The extensors are situated within six separate compartments. The first compartment contains abductor pollicis longus and extensor pollicis brevis. The second compartment contains extensors carpi radialis longus and brevis. The third compartment contains extensor pollicis longus. The extensor digitorum indicis and extensor digitorum communis are within the fourth compartment. Extensor digiti minimi is in the fifth, and extensor carpi ulnaris is in the sixth.
The intrinsic muscle groups are the thenar and hypothenar muscles (thenar referring to the thumb, hypothenar to the small finger), the dorsal and palmar interossei muscles (between the metacarpal bones) and the lumbrical muscles. The lumbricals arise from the deep flexor (and are special because they have no bony origin) and insert on the dorsal extensor hood mechanism.
The of a finger is the fleshy mass on the palmar aspect of the extremity of the finger. medilexicon.com > Medical Dictionary - 'Pulp Of Finger' Citing: Stedman's Medical Dictionary. 2006
The somatosensory cortex representation of the hand is a dynamic reflection of the fingers on the external hand: in syndactyly people have a clubhand of webbed, shortened fingers. However, not only are the fingers of their hands fused, but the cortical maps of their individual fingers also form a club hand. The fingers can be surgically divided to make a more useful hand. Surgeons did this at the Institute of Reconstructive Plastic Surgery in New York to a 32-year-old man with the initials O. G.. They touched O. G.'s fingers before and after surgery while using MRI brain scans. Before the surgery, the fingers mapped onto his brain were fused close together; afterward, the maps of his individual fingers did indeed separate and take the layout corresponding to a normal hand.
Phalanx bones are commonly fractured. A damaged tendon can cause significant loss of function in fine motor control, such as with a mallet finger. They can be damaged by cold, including frostbite and non-freezing cold injury (NFCI); and heat, including .
The fingers are commonly affected by diseases such as rheumatoid arthritis and gout. Individuals with diabetes often use the fingers to obtain blood samples for regular blood sugar testing. Raynaud's phenomenon and Paroxysmal hand hematoma are neurovascular disorders that affect the fingers.
Research has linked the Digit ratio to higher levels of testosterone, and to various physical and behavioral traits such as penis length and risk for development of alcohol dependence or video game addiction.
The name pinkie derives from Dutch pinkje, of uncertain origin. In English only the digits on the hand are known as fingers. However, in some languages the translated version of fingers can mean either the digits on the hand or feet. In English a digit on a foot has the distinct name of toe.
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