A leg is a limb on an animal's body that supports the rest of the animal above the ground between the ankle and the hip and is used for locomotion. The end of the leg furthest from the animal's body is often either modified or attached to another structure that is modified to disperse the animal's weight on the ground (see foot). In bipedal vertebrate animals, the two lower limbs are usually referred to as the 'legs' and the two upper limbs as the 'arms' or 'wings' as the case may be.
"Leg" is also a military term used to describe a service man (or woman) without airborne qualification. (no jump wings)
Legs typically come in even-numbered quantities. Many taxonomic groups are characterized by the number of legs its members possess.
Evolution
The leg has evolved several times, most significantly among arthropods (crustaceans, insects, arachnids, et cetera) and vertebrates. In both cases, they are thought to have first evolved for locomotion underwater, then have been exploited for movement over land.
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