A leg is a

weight-bearing In orthopedics, weight-bearing is the amount of weight a patient puts on an injured body part. Generally, it refers to a leg, ankle or foot that has been Bone fracture, fractured or upon which surgery has been performed, but the term can also be us ...

and

locomotive A locomotive is a rail transport, rail vehicle that provides the motive power for a train. Traditionally, locomotives pulled trains from the front. However, Push–pull train, push–pull operation has become common, and in the pursuit for ...

anatomical structure, usually having a columnar shape. During locomotion, legs function as "extensible struts". The combination of movements at all joints can be modeled as a single, linear element capable of changing length and rotating about an omnidirectional "hip" joint. As an anatomical

animal Animals are multicellular, eukaryotic organisms in the Biology, biological Kingdom (biology), kingdom Animalia (). With few exceptions, animals heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, ...

structure, it is used for locomotion. The distal end is often modified to distribute

force In physics, a force is an influence that can cause an Physical object, object to change its velocity unless counterbalanced by other forces. In mechanics, force makes ideas like 'pushing' or 'pulling' mathematically precise. Because the Magnitu ...

(such as a foot). Most animals have an even number of legs. As a component of furniture, it is used for the economy of materials needed to provide the support for the useful surface, such as the table top or chair seat.

Terminology

* Uniped: one leg, such as clams * Biped: two legs, such as humans and birds * Triped: three legs, which typically does not occur naturally in healthy animals * Quadruped: four legs, such as dogs and horses Many taxa are characterized by the number of legs: *

Tetrapod A tetrapod (; from Ancient Greek :wiktionary:τετρα-#Ancient Greek, τετρα- ''(tetra-)'' 'four' and :wiktionary:πούς#Ancient Greek, πούς ''(poús)'' 'foot') is any four-Limb (anatomy), limbed vertebrate animal of the clade Tetr ...

s have four legs. Squamates of genus '' Bipes'' have only two. Caecilians and many squamate lineages convergently lost their legs. * Panarthropoda: no less than four legs. Velvet worms and some arthropods have more than a dozen legs; a few species possess over one hundred. Despite what their names might suggest, centipedes ("hundred feet") may have fewer than twenty or more than 300 legs, and millipedes ("thousand feet") have fewer than 1,000 legs, but up to 750.

Components

A leg is a structure of gross anatomy, meaning that it is large enough to be seen unaided. The components depend on the animal. In humans and other mammals, a leg includes the

bone A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, ...

muscle Muscle is a soft tissue, one of the four basic types of animal tissue. There are three types of muscle tissue in vertebrates: skeletal muscle, cardiac muscle, and smooth muscle. Muscle tissue gives skeletal muscles the ability to muscle contra ...

tendon A tendon or sinew is a tough band of fibrous connective tissue, dense fibrous connective tissue that connects skeletal muscle, muscle to bone. It sends the mechanical forces of muscle contraction to the skeletal system, while withstanding tensi ...

s, ligaments, blood vessels,

nerve A nerve is an enclosed, cable-like bundle of nerve fibers (called axons). Nerves have historically been considered the basic units of the peripheral nervous system. A nerve provides a common pathway for the Electrochemistry, electrochemical nerv ...

s, and skin. In

insect Insects (from Latin ') are Hexapoda, hexapod invertebrates of the class (biology), class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (Insect morphology#Head, head, ...

s, the leg includes most of these things, except that insects have an

exoskeleton An exoskeleton () . is a skeleton that is on the exterior of an animal in the form of hardened integument, which both supports the body's shape and protects the internal organs, in contrast to an internal endoskeleton (e.g. human skeleton, that ...

that replaces the function of both the bones and the skin. Sometimes the end of the leg, or foot, is considered part of the leg; other times it is considered separate. Similarly, the hip joint or other place where the leg attaches to the main body may be considered separate or part of the leg.

Tetrapod legs

tetrapod A tetrapod (; from Ancient Greek :wiktionary:τετρα-#Ancient Greek, τετρα- ''(tetra-)'' 'four' and :wiktionary:πούς#Ancient Greek, πούς ''(poús)'' 'foot') is any four-Limb (anatomy), limbed vertebrate animal of the clade Tetr ...

anatomy, ''leg'' is used to refer to the entire limb. In human medicine, the precise definition refers only to the segment between the knee and the ankle. This lower segment is also called the ''shank'', and the front (anterior) of the segment is called the ''shin'' or ''pretibia''. In bipedal

s, the two lower limbs are referred to as the "legs" and the two upper limbs as "arms" or "wings" as the case may be. In quadrupedal tetrapods, the limbs are generally called forelegs, fore legs or front legs and hindlegs, hind legs or back legs.

Robotic leg

A robotic leg is moved by an

actuator An actuator is a machine element, component of a machine that produces force, torque, or Displacement (geometry), displacement, when an electrical, Pneumatics, pneumatic or Hydraulic fluid, hydraulic input is supplied to it in a system (called an ...

, which is a type of motor for moving or controlling a mechanism or system. It is operated by a source of energy, usually in the form of an electric current, hydraulic fluid pressure or pneumatic pressure, and converts that energy into motion.

Prosthetic leg

86 ACPS Atlanta 1996 Swimming General Views

A prosthetic leg is an artificial leg that is used to replace one that has been lost.

References

External links

* {{Use dmy dates, date=April 2024 Animal locomotion Animal anatomy Lower limb anatomy cs:Noha