Legs are the lower limbs of the human body, primarily used for standing, walking, running, and jumping. Each leg consists of several parts, including the thigh, knee, calf, ankle, and foot. The bones in the legs, such as the femur and tibia, provide structure and support, while muscles like the quadriceps and hamstrings enable movement. In many animals, legs serve similar functions, allowing for mobility and stability. The design of legs can vary greatly among species, with some having four legs for running fast, while others, like birds, have two legs adapted for perching and walking.