A leg is a weight-bearing and

locomotive A locomotive or engine is a rail transport vehicle that provides the Power (physics), motive power for a train. If a locomotive is capable of carrying a payload, it is usually rather referred to as a multiple unit, Motor coach (rail), motor ...

anatomical structure, usually having a

column A column or pillar in architecture and structural engineering is a structural element that transmits, through compression, the weight of the structure above to other structural elements below. In other words, a column is a compression member. ...

ar 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 structure it is used for locomotion. The

distal Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position pro ...

end is often modified to distribute

force In physics, a force is an influence that can change the motion of an object. A force can cause an object with mass to change its velocity (e.g. moving from a state of rest), i.e., to accelerate. Force can also be described intuitively as a p ...

(such as a

foot The foot ( : feet) is an anatomical structure found in many vertebrates. It is the terminal portion of a limb which bears weight and allows locomotion. In many animals with feet, the foot is a separate organ at the terminal part of the leg made ...

). 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: 1 leg, such as clams * Biped: 2 legs, such as humans and birds *

Triped Tripedalism (from the Latin tri = three + ped = foot) is locomotion by the use of three limbs. It has been said that parrots ( Psittaciformes) display tripedalism during climbing gaits, which was tested and proven in a 2022 paper on the subject, m ...

: 3 legs, which typically does not occur naturally in healthy animals * Quadruped: 4 legs, such as dogs and horses Many taxa are characterized by the number of legs: * Tetrapods have four legs. Squamates of genus '' Bipes'' have only two. Caecilians and many squamate lineages convergently lost their legs. * Panarthropoda: no less than 4 legs. Velvet worms and some arthropods have more than a dozen legs; a few species possess over 100. Despite what their names might suggest,

centipede Centipedes (from New Latin , "hundred", and Latin , " foot") are predatory arthropods belonging to the class Chilopoda (Ancient Greek , ''kheilos'', lip, and New Latin suffix , "foot", describing the forcipules) of the subphylum Myriapoda, an ...

s ("hundred feet") may have fewer than 20 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 bones,

muscle Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscl ...

s, tendons,

ligament A ligament is the fibrous connective tissue that connects bones to other bones. It is also known as ''articular ligament'', ''articular larua'', ''fibrous ligament'', or ''true ligament''. Other ligaments in the body include the: * Peritoneal li ...

s, blood vessels,

nerve A nerve is an enclosed, cable-like bundle of nerve fibers (called axons) in the peripheral nervous system. A nerve transmits electrical impulses. It is the basic unit of the peripheral nervous system. A nerve provides a common pathway for the e ...

s, and skin. In insects, the leg includes most of these things, except that insects have an exoskeleton that replaces the function of both the bones and the skin. Sometimes the end of the leg, or

, 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

In tetrapod anatomy, ''leg'' is used to refer to the entire

limb Limb may refer to: Science and technology * Limb (anatomy), an appendage of a human or animal *Limb, a large or main branch of a tree *Limb, in astronomy, the curved edge of the apparent disk of a celestial body, e.g. lunar limb *Limb, in botany, ...

. In human medicine the precise definition refers only to the segment between the

knee In humans and other primates, the knee joins the thigh with the leg and consists of two joints: one between the femur and tibia (tibiofemoral joint), and one between the femur and patella (patellofemoral joint). It is the largest joint in the hu ...

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 tetrapods, the two lower limbs are referred to as the "legs" and the two upper limbs as "arms" or "wings" as the case may be. *

Human leg The human leg, in the general word sense, is the entire lower limb (anatomy), limb of the human body, including the foot, thigh or sometimes even the hip or Gluteal muscles, gluteal region. However, the definition in human anatomy refers only to ...

Arthropod leg

* Arthropod leg

Robotic leg

robotic leg A robot leg (or robotic leg) is a mechanical leg that performs the same functions that a human leg can. The robotic leg is typically programmed to execute similar functions as a human leg. A robotic leg is similar to a prosthetic leg. However, a r ...

is moved by an

actuator An actuator is a component of a machine that is responsible for moving and controlling a mechanism or system, for example by opening a valve. In simple terms, it is a "mover". An actuator requires a control device (controlled by control signal) a ...

, 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 A hydraulic fluid or hydraulic liquid is the medium by which power is transferred in hydraulic machinery. Common hydraulic fluids are based on mineral oil or water. Examples of equipment that might use hydraulic fluids are excavators and backhoe ...

pressure or

pneumatic Pneumatics (from Greek ‘wind, breath’) is a branch of engineering that makes use of gas or pressurized air. Pneumatic systems used in Industrial sector, industry are commonly powered by compressed air or compressed inert gases. A central ...

pressure, and converts that energy into some kind of 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

* {{Authority control Animal locomotion Animal anatomy Lower limb anatomy cs:Noha