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|Hallux for left leg.
||Hallux, digitus I pedis, digitus primus pedis
In tetrapods, the hallux (big toe, great toe) is the innermost (most medial) toe of the foot. Despite its name it may not be the longest toe on the foot of some individuals. It is counted as digit I (one). The adjective form is "hallucal".
The name stems from the Latin for the same, similar to the pollex, which refers to the thumb, the corresponding digit of the hand.
In humans, the hallux is usually longer than the second toe. This is an inherited trait in humans, where the dominant gene causes a longer second toe ("Morton's toe" or "Greek foot") while the homozygous recessive genotype presents with the more common trait: a longer hallux. People with the rare genetic disease fibrodysplasia ossificans progressiva characteristically have a short hallux which appears to turn inward, or medially, in relation to the foot.
In birds with anisodactyl or heterodactyl feet, the hallux is opposed or directed backwards and allows for grasping and perching.
While the thumb is often mentioned as one of the signature characteristics in humans, this manual digit remains partially primitive and is actually present in all primates. In humans, the most derived digital feature is the hallux.
A common problem involving the big toe is the formation of bunions (hallux valgus), a deformity characterized by lateral deviation of the great toe, often erroneously described as an enlargement of bone or tissue around the joint at the head of the big toe.
The big toe is also the most common locus of ingrown nails and gout attacks.