Leg

For other senses of this word, see leg (disambiguation).

Diagram of an insect leg

In general, a leg is any of the parts of an animal's body that support the rest of the body above the ground, and are used for locomotion. Anatomists often use "leg" to refer to the portion from the knee down, and use "thigh" for the knee up.

Legs mostly come in even-numbered quantities that are characteristic of some taxonomic groups:

in vertebrates, 2 (the bipeds) or 4 (the quadrupeds);
in many familiar arthropods, 6, 8, or 12;
in some arthropods, more than a dozen and sometimes over 100 -- but despite what their names might suggest,
* centipedes seldom have exactly a hundred, and
* millipedes apparently never even approach a thousand.

In most quadrupeds and bipeds, legs consist of two main parts, attached to the body at one end, and to the foot at the other, and jointed at the knee.

The human leg

Shaved human female legs

The bones of the human leg are:

the femur (or thighbone), which attaches to the pelvis
the patella (kneecap)
the tibia (shinbone)
the fibula (calf bone)

The front edge of the tibia is not covered by a thick layer of muscle or fat: this is why being kicked in the shins is so painful.

Why do horses' knees bend backwards?

Although some quadrupeds such as horses appear to have reverse-bending knees on their back legs, the apparent backwards-bending knee is actually the equivalent of an ankle joint, with the entire lower leg being part of the "foot", and the apparent ankle being the equivalent of a finger joint. The actual "true" equivalent of the knee joint, the stifle joint, is internal to the horse's body, and bends in the same direction as other knees.

Leg

The human leg

Why do horses' knees bend backwards?

See also