Protection: Certain delicate and important organs are protected against mechanical injury by a casing of bones: for instance the brain, eyes, and inner ears are protected by the skull; the spinal cord by the vertebral column ; and the heart and lungs by the thoracic cage.

Movement and locomotion: Many bones of the skeleton act as levers. When muscles pull on the levers they produce movements, for instance the chewing action of the jaws, the breathing movements of the thoracic cage etc. Locomotion is the result of coordinated action of muscles on the limb bones, to which they are attached by tendons.

Muscle attachment: To produce effective movement of any part of the skeleton, the muscles are attached securely to it by flexible connective tissue bands called tendons or ligaments.

Hemopoiesis: The blood corpuscles are produced in the red bone marrow present in the spongy bones of vertebrae and the sternum, scapula and in the ends of long bones, such as thehumerus and femur.

Storage of Calcium and Phosphate: which are released for several functions of the body.

The adult human skeleton consists of 206 bones in the form of long bones (femur, humerus etc.); short bones (wrist and ankle bones); flat bones (skull bones, ribs, shoulder blades) and irregular bones (vertebrae, lower jaw, etc). The entire skeleton consists of two main parts: (A) the axial skeleton and (B) the appendicular skeleton. The relationship is shown in Figure 20.1.