Human Leg - Anatomy

Anatomy

In human anatomical terms, the leg is the part of the lower extremity that lies between the knee and the ankle, the thigh is between the hip and knee and the term "lower extremity" is used to describe the colloquial leg. This article generally follows the common usage.

The leg from the knee to the ankle is called the cnemis /ˈniːmɪs/ or crus. The calf is the back portion and the shin is the front.

Evolution has provided the human body with two distinct features: the specialization of the upper limb for visually guided manipulation and the lower limb's development into a mechanism specifically adapted for efficient bipedal gait. While the capacity to walk upright is not unique to humans, other primates can only achieve this for short periods and at a great expenditure of energy. The human adaption to bipedalism is not limited to the leg, however, but has also affected the location of the body's center of gravity, the reorganisation of internal organs, and the form and biomechanism of the trunk. In humans, the double S-shaped vertebral column acts as a shock-absorber which shifts the weight from the trunk over the load-bearing surface of the feet. The human legs are exceptionally long and powerful as a result of their exclusive specialization to support and locomotion — in orangutans the leg length is 111% of the trunk; in chimpanzees 128%, and in humans 171%. Many of the leg's muscles are also adapted to bipedalism, most substantially the gluteal muscles, the extensors of the knee joint, and the calf muscles.