A limb (from the Old English ''lim''), or extremity, is a

joint A joint or articulation (or articular surface) is the connection made between bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the skeleton in most vertebrate animals. Bones protect the various organs of th ...

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 () is any organic, life, living system that functions as an individual entity. All organisms are c ...

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 gait Gait is the pattern of Motion (physics), movement of the limb (anatomy), limbs of animals, including Gait (human), humans, during Animal locomotion, locomotion over a solid substrate. M ...

walking

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

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 ...

arm

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

at the

shoulder The human shoulder is made up of three bones: the clavicle The clavicle, or collarbone, is a slender, S-shaped long bone approximately 6 inches (15 cm) long that serves as a strut between the scapula, shoulder blade and the sternum (bre ...

and legs are connected at the

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 Object may refer to: General meanings * Object (philosophy), a thing, being, or concept ** Entity, something that is tangible and within the grasp of the senses ** Object (abstract), an o ...

. 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 Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemist ...

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 extant Extant is the opposite of the word extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a sp ...

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 ...

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 ...

. 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

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 vertebrates is an area of active research in both developmental biology, developmental and evolutionary biology, with much of the latter work focused on the transition from fin to limb (anatomy), limb. Limb formation begins in ...

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 A multicellular organism is an organism that con ...

s. All jawed vertebrates surveyed so far organize their developing

limb bud The limb bud is a structure formed early in vertebrate limb development. As a result of interactions between the ectoderm and underlying mesoderm, formation occurs roughly around the fourth week of development. In human embryonic development, the ...

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 layer A germ layer is a primary layer of cells that forms during embryonic development. The three germ layers in ve ...

(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.

References

{{Authority control

Terminology

Development

See also

References