Leg

The leg is the lower part of the body in humans and many animals. Its primary function is to support the weight of the body and enable movement such as walking, running, and jumping. In humans, the leg extends from the hip joint (where the pelvis and thighbone connect) to the foot.

The leg consists of bones, muscles, tendons, ligaments, blood vessels, and nerves. The interaction of these components allows the leg to function as both a rigid support structure and a flexible instrument of movement with considerable strength.

Structure of the bones

The largest bone in the leg is the femur (thighbone), which is the longest bone in the human body. Below the knee lie two bones: the tibia (the front bone that bears weight) and the fibula (the thinner bone on the side). Within the knee is a small bone called the patella, which faces the joint between the thigh and lower leg. The foot contains many small bones, including the calcaneus (heel bone) and the bones of the toes.

Muscles and movement

The major muscles of the leg include the quadriceps (the front thigh muscles that straighten the knee), the hamstrings (the back thigh muscles that bend the knee), and the calf muscles (the gastrocnemius and soleus) that lift the foot downward. During walking, these muscles work in coordinated sequence to shift weight from one foot to the other.

Use of the term in animals

In zoology, the term leg is applied to the support limbs of various organisms: quadrupeds (four-legged animals), birds (two-legged), and insects (typically six-legged). Spiders have eight legs. The structure of legs varies according to the locomotion style and habitat of the organism.