HOME

TheInfoList



OR:

A leg is a weight-bearing and
locomotive A locomotive or engine is a rail transport vehicle that provides the 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, railcar or power car; t ...
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 Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and go through an ontogenetic stage ...
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 pr ...
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 ...
(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 ma ...
). 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 A uniped (from Latin ''uni-'' "one" and ''ped-'' "foot") is a person or creature with only one foot and one leg, as contrasted with a biped (two legs) and a quadruped (four legs). Moving using only one leg is known as unipedal movement. Many bival ...
: 1 leg, such as clams * Biped: 2 legs, such as humans and birds * Triped: 3 legs, which typically does not occur naturally in healthy animals * Quadruped: 4 legs, such as dogs and horses Many
taxa In biology, a taxon (back-formation from ''taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular nam ...
are characterized by the number of legs: *
Tetrapod Tetrapods (; ) are four-limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant and extinct amphibians, sauropsids ( reptiles, including dinosaurs and therefore birds) and synapsids (pelycosaurs, extinct ther ...
s 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, centipedes ("hundred feet") may have fewer than 20 or more than 300 legs, and
millipede Millipedes are a group of arthropods that are characterised by having two pairs of jointed legs on most body segments; they are known scientifically as the class Diplopoda, the name derived from this feature. Each double-legged segment is a re ...
s ("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, an ...
s,
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 m ...
s,
tendon A tendon or sinew is a tough, high-tensile-strength band of dense fibrous connective tissue that connects muscle to bone. It is able to transmit the mechanical forces of muscle contraction to the skeletal system without sacrificing its abilit ...
s,
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 ...
s,
blood vessel The blood vessels are the components of the circulatory system that transport blood throughout the human body. These vessels transport blood cells, nutrients, and oxygen to the tissues of the body. They also take waste and carbon dioxide awa ...
s,
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 ...
s, and
skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other animal coverings, such as the arthropod exoskeleton, have different d ...
. In
insect Insects (from Latin ') are pancrustacean 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 (head, Thorax (ins ...
s, the leg includes most of these things, except that insects have an
exoskeleton An exoskeleton (from Greek ''éxō'' "outer" and ''skeletós'' "skeleton") is an external skeleton that supports and protects an animal's body, in contrast to an internal skeleton ( endoskeleton) in for example, a human. In usage, some of the ...
that replaces the function of both the bones and the skin. Sometimes the end of the leg, or
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 ma ...
, is considered part of the leg; other times it is considered separate. Similarly, the
hip joint In vertebrate anatomy, hip (or "coxa"Latin ''coxa'' was used by Celsus in the sense "hip", but by Pliny the Elder in the sense "hip bone" (Diab, p 77) in medical terminology) refers to either an anatomical region or a joint. The hip region ...
or other place where the leg attaches to the main body may be considered separate or part of the leg.


Tetrapod legs

In
tetrapod Tetrapods (; ) are four-limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant and extinct amphibians, sauropsids ( reptiles, including dinosaurs and therefore birds) and synapsids (pelycosaurs, extinct ther ...
anatomy Anatomy () is the branch of biology concerned with the study of the structure of organisms and their parts. Anatomy is a branch of natural science that deals with the structural organization of living things. It is an old science, having its ...
, ''leg'' is used to refer to the entire limb. 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 ...
and the
ankle The ankle, or the talocrural region, or the jumping bone (informal) is the area where the foot and the leg meet. The ankle includes three joints: the ankle joint proper or talocrural joint, the subtalar joint, and the inferior tibiofibular joi ...
. This lower segment is also called the ''shank'', and the front (anterior) of the segment is called the ''shin'' or ''pretibia''. In bipedal
tetrapod Tetrapods (; ) are four-limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant and extinct amphibians, sauropsids ( reptiles, including dinosaurs and therefore birds) and synapsids (pelycosaurs, extinct ther ...
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. *
Human leg The human leg, in the general word sense, is the entire lower limb of the human body, including the foot, thigh or sometimes even the hip or gluteal region. However, the definition in human anatomy refers only to the section of the lower limb ...


Arthropod leg

*
Arthropod leg The arthropod leg is a form of jointed appendage of arthropods, usually used for walking. Many of the terms used for arthropod leg segments (called podomeres) are of Latin origin, and may be confused with terms for bones: ''coxa'' (meaning hip, plu ...


Robotic leg

A robotic leg 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) ...
, which is a type of
motor An engine or motor is a machine designed to convert one or more forms of energy into mechanical energy. Available energy sources include potential energy (e.g. energy of the Earth's gravitational field as exploited in hydroelectric power ge ...
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 backhoes ...
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 industry are commonly powered by compressed air or compressed inert gases. A centrally located and el ...
pressure, and converts that energy into some kind of motion.


Prosthetic leg

A
prosthetic In medicine, a prosthesis (plural: prostheses; from grc, πρόσθεσις, prósthesis, addition, application, attachment), or a prosthetic implant, is an artificial device that replaces a missing body part, which may be lost through tra ...
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