Leg

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A leg is the part of 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.

Legs typically come in even-numbered quantities. Many taxonomic groups are characterized by the number of legs its members possess.

• Uniped: 1
• Biped: 2
• Tripedal: 3
• Quadruped: 4
• Quinped: 5
• Arthropoda: 4, 6, 8, 12, or 14
  • Some arthropods have more than a dozen legs; a few species possess over 100. Despite what their names might suggest,
    • Centipedes typically have fewer than one hundred legs
    • Millipedes have fewer than one thousand legs.

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 ever less desperate conditions as the generations passed.

See also

• Body plan
• Arthropod leg
• Terrestrial locomotion in animals

• Human leg

Sources

http://www2.merriam-webster.com/cgi-bin/mwmednlm