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The skeletal system consists of bones, cartilages, tendons, and ligaments. Bones are very rigid. They support and protect internal organs, and assist in body movement. There are 206 bones in the average adult skeleton. It is divided into the skull, spinal column, thoracic cage, upper and lower limbs and the girdles. The bones of the skull are organized into cranial vault, facial bones, and auditory ossicles. The vertebral column consists of cervical vertebrae, thoracic vertebrae, lumbar vertebrae, sacral bone, and coccygeal bone (coccyx). The vertebral column supports the weight of the head and trunk, protects the spinal cord, and provides a site for muscle attachment. The thoracic cage protects the internal organs. It consists of the thoracic vertebrae, the ribs with their associated costal (rib) cartilages, and the sternum. The basic part of the thoracic cage is formed by the ribs. Each rib consists of the head, the neck, and the body. The sternum is a long bone in the middle of the thorax. A typical vertebra consists of a body, an arch, and various processes. The upper limb consists of the humerus, a cubital (elbow) joint, the ulna, and the radius. The wrist is composed of carpal bones. The hand consists of five metacarpal bones. The pelvic girdle supports the weight of the body and protects internal organs. The thigh contains the femur. The knee is the joint located between the femur and the tibia. The leg consists of the tibia and the fibula. The ankle consists of tarsal bones. The foot consists of metatarsal bones.
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