Leg (anatomy)

Leg (anatomy), in anatomy, one of the paired limbs of a vertebrate, used chiefly for supporting the body and for locomotion. The term leg is sometimes applied to one of the paired appendages of an insect, spider, or other arthropod. In humans, the leg extends from the hipbone to the foot.

The upper part of the human leg, the thigh, is supported by the femur—the longest and strongest bone of the body. The upper end of the femur is rounded and fits into a cavity in the hip bone, forming a ball-and-socket joint. Ball-and-socket joints permit circular motion, and the hip joint allows the leg to move freely in almost any direction. This joint also helps distribute body weight evenly over the head of the femur. At the knee, the femur connects to the tibia, or shinbone, to form a hinge joint. Hinge joints permit back-and-forth movement similar to the motion of a hinged door. This joint is protected in front by a small triangular bone called the patella, or kneecap, which lies in the tendon covering the joint.

The tibia is one of the two long bones of the lower leg. It forms the front of the leg while the fibula, which is somewhat smaller, forms the side of the leg. The upper end of the fibula joins the tibia just below the knee joint. The tibia and fibula connect to the talus, or anklebone, at the ankle joint, which is a hinged joint.

The gluteus maximus is a large, wide muscle that covers the back of the hip joint and comprises the buttocks. It extends and rotates the leg, and is one of four major muscles of the thigh. The other major thigh muscles are the sartorius, the quadriceps, and the hamstring. The sartorius, the longest muscle in the body, runs from the hipbone diagonally across the front of the thigh to the inside of the knee, and bends the leg at both the hip and the knee. The quadriceps, comprised of four muscles that cover the front of the thigh, straighten the leg at the knee. The hamstrings, three large muscles at the back of the thigh, bend the knee and rotate the leg from side to side. Each hamstring muscle is attached to the tibia by a hamstring tendon, which may be felt near the back of the knee.

The major muscles of the lower leg are the gastrocnemius and the soleus. These muscles lie at the back of the leg where the gastrocnemius comprises a large portion of the calf muscle. The gastrocnemius and the soleus straighten the foot and are important in walking. They are connected to the heel bone by the Achilles tendon, the strongest and thickest tendon of the body. Muscles in the front and on the sides of the leg provide balance and bend the foot up and to the side.

The femoral artery, deep in the thigh, is the major vessel that supplies blood to the thigh, while the anterior and posterior tibial arteries are primary blood vessels in the lower leg. The major nerve in the leg is the sciatic nerve —the largest nerve in the body, which carries motor information to and sensory information from most of the leg and foot. Another primary nerve is the tibial nerve, which is the largest of two branches off the sciatic nerve in the lower leg.