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In zoology, dactyly is the arrangement of digits (fingers and toes) on the hands, feet, or sometimes wings of an animal. It comes from the Greek word daktulos, meaning "finger".
Syndactyly
In birds, two of three toes in front are partially fused to make digging easier. This is characteristic of Coracciformes (Kingfishers, Bee-eaters, Rollers, and relatives).
In humans, syndactyly is when two digits of the hands or feet are fused together. While syndactyly is considered normal in birds and in some mammals, such as the siamang, it is very unusual in humans.
Syndactyly can be full or partial, and is present at birth (congenital). In early fetal development, webbing (syndactyly) of the toes and fingers is normal. At about 16 weeks of gestation, the toes and fingers usually separate and the webbing disappears. But in some fetuses, this separation does not occur. The exact cause is not known. The condition can be hereditary.
Syndactyly usually does not affect the function of the foot or toes and should not interfere with walking. Although webbing of the fingers usually does not affect the function of the hand, it can affect function of the fingers. Treatment of webbed toes and fingers is corrective or reconstructive surgery, which involves general anesthesia. These repairs are usually done when a child is between 6 months and 2 years old.
Zygodactyly
Zygodactyl refers to birds which have "yoked" feet, that is with two toes facing forward and two back. This arrangement is most common in arboreal species, particularly those that climb tree trunks or clamber through foliage.
Zygodactyly occurs in the woodpeckers and flickers, nuthatches, and parrots.
Ectrodactyly
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.
Polydactyly
An excess of digits is called polydactyly or hyperdactyly, such as in the rare case that a person has six fingers or toes on a single hand or foot.
Hypodactyly
A lack of digits not caused by an amputation is called hypodactyly.
See also
"Syndactyly"