Dactyly

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Human foot with partial simple syndactyly.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Synonyms and Keywords: webbing of the digits

Overview

In biology, dactyly is the arrangement of digits (fingers and toes) on the hands, feet, or sometimes wings of a tetrapod animal. It comes from the Greek word δακτυλος = "finger".

Classification

Sometimes the ending "-dactylia" is used. The derived adjectives end with "-dactyl" or "-dactylous".

Pentadactyly

Pentadactyly (from Greek pente-="five" plus δακτυλος = "finger") is the condition of having five digits on each limb. It appears that all land vertebrates are descended from an ancestor with a pentadactyl limb, although many species have now lost or transformed some or all of their digits by the process of evolution. Despite the individual variations listed below, the relationship to the original five-digit 'model' can be traced. This phenomenon featured in the work of Charles Darwin who noteably said; "What could be more curious than that the hand of man formed for grasping, that of a mole, for digging, the leg of a horse, the paddle of a porpoise and the wing of a bat, should all be constructed on the same pattern and should include similar bones and in the same relative positions?" Darwin was suggesting that the pentadactyl limb represents some of the strongest evidence for the theory of evolution as it indicates a common ancestry for all land vertebrates.

Tetradactyly

Tetradactyly (from Greek tetra-="four" plus δακτυλος = "finger") is the condition of having four digits on a limb, as in many amphibians and birds. Some mammals also exhibit tetradactyly (for example the hind limbs of dogs and cats).

Tridactyly

Tridactyly (from Greek tri- = "three" plus δακτυλος = "finger") is the condition of having three digits on a limb, as in the Rhinoceros and ancestors of the horse such as Protohippus and Hipparion. These belong to the Perissodactyla. Some birds also have three toes.

Didactyly

Didactyly (from Greek di-="two" plus δακτυλος = "finger") or bidactyly is the condition of having two digits on each limb, as in the Two-toed Sloth, Choloepus didactylus. In humans this name is used for an abnormality in which the middle digits are missing, leaving only the thumb and fifth finger. Cloven-hoofed mammals (such as deer, sheep and cattle - 'Artiodactyla') walk on two digits.

Monodactyly

Monodactyly (from Greek monos- = "one" plus δακτυλος = "finger") is the condition of having a single digit on a limb, as in modern horses. These belong to the Perissodactyla.

Syndactyly

Syndactyly (from Greek συν- = "together" plus δακτυλος = "finger") is a condition where two or more digits are fused together. It occurs normally in some mammals, such as the siamang. It occurs as an unusual condition in humans.

Syndactyly can be simple or complex. In simple syndactyly, adjacent fingers or toes are joined by soft tissue. In complex syndactyly, the bones of adjacent digits are fused. The kangaroo exhibits complex syndactyly.

Simple syndactyly can be full or partial, and is present at birth (congenital). In early human fetal development, webbing (syndactyly) of the toes and fingers is normal. At about 16 weeks of gestation, apoptosis takes place and an enzyme dissolves the tissue between the fingers and toes, and the webbing disappears. In some fetuses, this process does not occur completely between all fingers or toes and some residual webbing remains. The exact cause is not known. In cases, this condition appears to be hereditary.

In the case of human feet, syndactyly does not affect the function of the foot or toes and does not interfere with walking or swimming or any other activities. Although webbing of the fingers usually does not affect the function of the hand, it can impair function of the fingers. Surgery may be performed to separate webbed fingers or toes. As with any surgery, there are risks of complications. This procedure involves local anesthesia with a sedative and can be done just with a local without the sedative for adults if desired. In addition to the incision between the toes, sometimes it is necessary to remove some skin from elsewhere on the body to graft into the newly exposed space between the toes.

In the case of webbed toes, surgical separation is a purely cosmetic operation with no medical benefits.

Polydactyly

Polydactyly (from Greek πολυ- = "many" plus δακτυλος = "finger") (or hyperdactyly, from Greek hyper- = "too many" plus δακτυλος = "finger") is when a limb has more than five digits. This can be:-

  • As a result of congenital abnormality in a normally pentadactyl animal. Polydactyly is very common among domestic cats.
  • Normality in some early tetrapod aquatic animals, such as Acanthostega gunnari (Jarvik 1952), which is one of an increasing number of genera of stem-tetrapods known from the Upper Devonian, which are providing insights into the appearance of tetrapods and the origin of limbs with digits. For more information, see polydactyly.

Hypodactyly

Hypodactyly (from Greek hypo- = "too few" plus δακτυλος = "finger") is having too few digits when not caused by an amputation.

Ectrodactyly

Ectrodactyly is the congenital absence of all or part of one or more fingers or toes. This term is used for a range of conditions from aphalangia (in which some of the phalanges or finger bones are missing), to adactyly (the absence of a digit).

A fusing of almost all digits on all of the hands and feet is ectrodactyly. News anchor Bree Walker is probably the best-known person with this condition, which affects about one in 91,000 people. It is conspicuously more common in the Vadoma in Zimbabwe.

de:Syndaktylie he:דקטיליה nl:Syndactylie sr:Синдактилија fi:Syndaktylia sv:Syndaktyli



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