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A limb (from the Old English ''lim''), or extremity, is a
joint A joint or articulation (or articular surface) is the connection made between bones in the body which link the skeletal system into a functional whole.Saladin, Ken. Anatomy & Physiology. 7th ed. McGraw-Hill Connect. Webp.274/ref> They are construc ...

joint
ed bodily
appendage An appendage (or outgrowth) is an external body part, or natural prolongation, that protrudes from an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system ...
that
humans Humans (''Homo sapiens'') are the most populous and widespread species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species ...
and many other animals use for
locomotion Locomotion means the act or ability of an entity or person to transport or move oneself from place to place. Locomotion or Loco-Motion may refer to: Motion * Motion (physics) *Specific types of motion ** Animal locomotion *** Terrestrial locomoti ...
such as
walking Walking (also known as ambulation) is one of the main gaits of terrestrial locomotion among legged animals. Walking is typically slower than running Running is a method of terrestrial locomotion allowing humans and other animals to move ...

walking
,
running Running is a method of terrestrial locomotion allowing humans and other animals to move rapidly on foot. Running is a type of gait characterized by an aerial phase in which all feet are above the ground (though there are exceptions). This is ...

running
and
swimming Swimming is the self-propulsion of a person through water Water is an Inorganic compound, inorganic, Transparency and translucency, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the ...
, or for
prehensile A prehensile tail. Prehensility is the quality of an appendage An appendage (or outgrowth) is an external body part, or natural prolongation, that protrudes from an organism In biology, an organism (from Ancient Greek, Greek: ὀργ ...
grasping or
climbing Climbing is the activity of using one's hands, feet, or any other part of the body to ascend a steep topographical object. It is done for locomotion, recreation and competition, and within trades that rely on ascension; such as emergency res ...
. In the human body,
arm In human anatomy, the arm is the part of the upper limb The upper Limb (anatomy), limbs or upper extremities are the forelimbs of an upright posture, upright-postured tetrapod vertebrate, extending from the scapulae and clavicles down to and incl ...
s and
legs A leg is a weight-bearing and animal locomotion, locomotive 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, ...
are commonly called
upper limb The upper Limb (anatomy), limbs or upper extremities are the forelimbs of an upright posture, upright-postured tetrapod vertebrate, extending from the scapulae and clavicles down to and including the digit (anatomy), digits, including all the muscul ...
s and
lower limb Lower may refer to: *Lower (surname)Lower is a surname. Notable people with the surname include: * Arthur R. M. Lower (1889–1988) Canadian historian * Britt Lower (born 1985), American actress * Cyrus B. Lower (1843–1924), American Civil War ...
s, respectively. Arms are connected to the
torso or trunk
torso or trunk
at the
shoulder The human shoulder is made up of three bones: the clavicle (collarbone), the scapula (shoulder blade), and the humerus (upper arm bone) as well as associated muscles, ligaments and tendons. The articulations between the bones of the shoulder make ...
and legs are connected at the
hip girdles
hip girdles
. Many animals can use their
forelimb A forelimb or front limb is one of the bilateral symmetry, paired joint, articulated appendages (limb (anatomy), limbs) attached on the cranial (anterior (anatomy), anterior) end of a terrestrial animal, terrestrial tetrapod vertebrate's torso. Wi ...
s (which are homologous to arms in humans) to carry and
manipulate Manipulation may refer to: As underhand influence *Psychological manipulation **Crowd manipulation *Data manipulation *Media manipulation *Internet manipulation *Market manipulation In a physical context *Card manipulation *Coin manipulation *Hat ...
objects, while some can use them to achieve
flight Flight or flying is the process by which an object (physics), object motion (physics), moves through a space without contacting any planetary surface, either within an atmosphere (i.e. air flight or aviation) or through the vacuum of outer space ...
. Some animals can also use
hind limbsA hindlimb or back limb is one of the bilateral symmetry, paired joint, articulated appendages (limb (anatomy), limbs) attached on the Caudal (anatomical term), caudal (posterior (anatomy), posterior) end of a terrestrial animal, terrestrial tetrapod ...
for manipulation. Human legs and
feet The foot (plural: feet) is an anatomical structure found in many vertebrates. It is the terminal portion of a Limb (anatomy), limb which bears weight and allows Animal locomotion, locomotion. In many animals with feet, the foot is a separate org ...

feet
are specialized for two-legged locomotion – most other mammals walk and run on all four limbs. Human arms are weaker, but very mobile, allowing them to reach at a wide range of distances and angles, and end in specialized
hand A hand is a prehensile, multi- fingered appendage located at the end of the forearm The forearm is the region of the upper limb between the Elbow-joint, elbow and the wrist. The term forearm is used in anatomy to distinguish it from the arm, ...

hand
s capable of grasping and fine manipulation of objects. Though human dexterity is relatively unique, grasping behavior is widespread among
tetrapod Tetrapods (; ) are four-limbed animals constituting the superclass Tetrapoda (). It includes Neontology#Extant taxa vs. extinct taxa, extant and extinct amphibians, reptiles (including dinosaurs and therefore birds), and synapsids (including mam ...
s.


Terminology

The overall patterns of the forelimbs and hindlimbs are so similar ancestrally, and branch out in similar ways; that they are given shared names. Limbs are attached to the
pectoral girdle The shoulder girdle or pectoral girdle is the set of Bone, bones in the appendicular skeleton which connects to the arm on each side. In humans it consists of the clavicle and scapula; in those species with three bones in the shoulder, it consists ...
or
pelvic girdle The pelvis (plural pelves or pelvises) is the lower part of the trunk, between the abdomen The abdomen (colloquially called the belly, tummy, midriff or stomach) is the part of the body between the thorax (chest) and pelvis, in humans and in o ...

pelvic girdle
. The one bony element of the upper limb is the ''stylopodium'', the two bones of the lower limb are the ''zeugopodium''. The distal portion of the limbs, that is, the hands or feet, are known as ''autopodia''. Hands are technically known as the ''manus'', and feet as the ''pes'', which are both composed of
carpals
carpals
and digits. As
metapodialMetapodials are long bones of the hand (metacarpals) and feet (metatarsals) which connect the digits to the lower leg bones. In humans, five are present in each hand and foot. In quadrupeds, these form the lower limb, rather than being part of the ex ...
s, the
metacarpals In human anatomy, the metacarpal bones or metacarpus, form the intermediate part of the skeleton, skeletal hand located between the phalanges of the fingers and the carpal bones of the wrist which forms the connection to the forearm. The metacarpal ...
and
metatarsals The metatarsal bones, or metatarsus are a group of five long bones in the foot The foot (plural: feet) is an anatomical Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology Biology is the natural science that studies l ...
are analogous to each other.


Development

Limb development Limb development in vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals ...
is controlled by
Hox gene Hox genes, a subset of homeobox genes, are a group of related genes that specify regions of the body plan of an embryo An embryo is the early stage of development of a multicellular organism. In general, in organism In biology, an ...
s. All jawed vertebrates surveyed so far organize their developing
limb bud
limb bud
s in a similar way. Growth occurs from proximal to distal part of the limb. On the distal end, the differentiation of skeletal elements occurs in an
apical ectodermal ridge The apical ectodermal ridge (AER) is a structure that forms from the ectoderm The ectoderm is one of the three primary germ layers formed in early embryonic development. It is the outermost layer, and is superficial to the mesoderm (the middle l ...
(AER) which expands in rays. A
Zone of Polarizing Activity The zone of polarizing activity (ZPA) is an area of mesenchyme that contains signals which instruct the developing limb bud to form along the anterior/posterior axis. Limb bud is undifferentiated mesenchyme enclosed by an ectoderm covering. Eventu ...
(ZPA) at the rear part of the AER coordinates the differentiation of digits.


See also

*
Anatomical terms of location Standard anatomical terms of location deal unambiguously with the anatomy of animals, including humans. Terms used generally derive from Latin or Greek language, Greek roots and used to describe something in its standard anatomical position. This ...
*
Anatomical terms of motion Motion Image:Leaving Yongsan Station.jpg, 300px, Motion involves a change in position In physics, motion is the phenomenon in which an object changes its position (mathematics), position over time. Motion is mathematically described in terms of ...
*
Orthosis Orthotics ( el, Ορθός, translit=ortho, lit=to straighten, to align) is a medical specialty A medical specialty is a branch of medical practice that is focused on a defined group of patients, diseases, skills, or philosophy. Examples incl ...
*
Phantom limb A phantom limb is the sensation that an amputation, amputated or missing limb (anatomy), limb is still attached. Approximately 80 to 100% of individuals with an amputation experience sensations in their amputated limb. However, only a small perc ...
* Descending limb of loop of Henle *
Ascending limb of loop of Henle Within the nephron of the kidney, the ascending limb of the loop of Henle is a segment of the heterogenous loop of Henle downstream of the Descending limb of loop of Henle, descending limb, after the sharp bend of the loop. This part of the nephron# ...


References

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