A limb is any prominent extension that projects from the main body of an organism. In animals the term usually refers to appendages such as arms, legs, wings or fins that serve for movement, support or manipulation. In plants and fungi the word is sometimes applied more loosely to branches or large projecting structures. The concept connects form and function: a limb’s shape reflects its mechanical and ecological roles.

Structure and components

Animal limbs typically combine a skeletal framework, muscles, joints, nerves and blood vessels. For example, a human upper limb includes regions commonly named the arm, forearm and hand, while the lower limb includes the thigh, leg (lower leg) and foot. These parts are organized around joints that permit motion and are stabilized by ligaments and muscles. See anatomical overviews of the trunk and how limbs attach to it.

Variations and examples

  • Vertebrate limbs: arms and legs in mammals, wings in birds, forelimbs and hindlimbs in reptiles and amphibians.
  • Fins in fishes that evolved into tetrapod limbs with digits in early land animals.
  • In plants, a limb may refer to a large branch or bough that projects from the main stem.

Function and importance

Limbs perform diverse tasks: locomotion (walking, swimming, flying), manipulation (grasping, tool use), display, defence and support. In humans and other primates, upper limbs permit fine motor tasks such as writing or tool-making; lower limbs provide weight-bearing and ambulation—the familiar human legs used for standing and walking, and the limbs of a man or woman are central to many activities.

Development, evolution and medical aspects

Limbs develop during embryogenesis from limb buds under genetic and molecular control. Across evolutionary time, structures such as fins transformed into weight-bearing limbs that allowed vertebrates to colonize land. Clinically, limbs are the focus of orthopedics and rehabilitation: injuries to bones, muscles or joints can impair function, and conditions affecting the normal human body may alter limb use. Prosthetics and surgery restore or replace lost limb function.

Distinctions: "Limb" often overlaps with terms like "appendage" or "branch," but is usually reserved for substantial projecting parts involved in movement or support rather than small projections such as hairs or spines.