SKELETON                                                                                                                                   The skeleton system is a mobile framework made up of 206 bones, approximately half of which are in the hand and feet. Although individual bones are rigid, the skeleton as a whole is remarkably flexible and allows the human body a huge range of movement. The skeleton serves as an anchorage for the skeleton muscles, and as a protective cage for the body's internal organs. Female bones, and usually smaller the pelvis is shallower and has a wider cavity.                                                   SKULL                                                                                                                                    The skull is the most complicated bone structure of the body but every feature serves a purpose. Internally, the main hollow chamber of the skull has three levels that support the brain, with every bump and hallow corresponding to the shape of the brain. Underneath and towards the back of the skull is a large round hole, the foramen magnum, through which the spinal cord passes. To the front of this are many smaller openings through which nerves, arteries, and veins pass to and from the brain. The roof of the skull is formed from four thin, curved bones that are firmly fixed together form the age of about two years. At the front of the skull are the two orbits, which contain the eyeballs, and a central hole for the airway of the nose. The jaw bone hinges on either side at ear level.       SPINE                                                                                                                                     The spine(or vertebral column) has two main functions: it serves as a protective surrounding for the delicate spinal nd forms the supporting back bone of the skeleton. The spine consists of 24 separate differently shaped bones (vertebrae) with a curved, triangular bone (the sacrum) at the bottom. The sacrum is made up of of fused vertebrae is a disc of cartilage tat cushions the bones during movement. The top two vertebrae differ in appearance from the others and work as a pair: The first, called the atlas, rotates around a stout vertical peg on the second, the axis, This arrangement allows the skull to move freely up and down, and from side to side.                                                                                             BONES AND JOINTS                                                                                                                                  Bones from the body's hard, strong skeletal framework. each bone has a hard, compact exterior surrounding a spongy, lighter interior. The long bones of the arms and legs, such as the femur(thigh bone), have a central cavity containing bone marrow. Bones are composed chiefly of calcium, phosphorus, and a fibrous substance known as collagen. bones meet at joints, which are of several different types. For example, the hip is a ball-and-socket joint that allows the femur a wide range of movement, whereas finger joints are simple hinge that allow only bending and straightening. joins are held in place by the smooth hyaline cartilage that covers the bone ends and by the synovial membrane that lines and lubricates the joints