The skeleton is a complex of hard structures. It consists of separate bones joined to each other by means of connective cartilaginous or bony tissue, which together make up the passive locomotor system. There are over 200 bones in the skeleton. The bones of the skeleton are the spine and the chest. The spine consists of such parts as: cervical, thoracic, lumbar, sacral and the coccyx. There are about 34 vertebrae in the spine of the adult. The spinal column consists of seven cervical vertebrae, twelve thoracic vertebrae, five lumbar vertebrae, five sacral vertebrae and from one to five vertebrae which form the coccyx. The largest vertebrae in the spine are the lumbar vertebrae. The lumbar vertebrae have oval bodies. The thorax is composed of thoracic vertebrae, the breastbone, which is a long bone in the middle of the chest, and twelve pairs of ribs. The skeleton contains two pairs of limbs, or extremities: upper and lower. The upper extremity includes the arm, the forearm and the hand. The lower extremity is formed by the thigh, the leg, and the foot.
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The mechanical functions of the skeleton include protection, support, and movement.
Support is provided by attachment of the soft tissues and organs to the different parts of the skeleton.
Movement is possible because the bones have the structure of long and short levers connected by mobile articulations and set in motion by muscles, which are regulated by the nervous system.
Protection is provided by the vertebral canal, which protects the spinal cord; a bone case, the skull, which protects the brain; the thoracic cage, which protects vitally important organs of the thoracic cavity (heart, lungs); and the pelvis, which protects the reproductive organs.