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the skeleton.
the skeleton is composed of bones. in the adult the skeleton has over 200 bones.
the bones of the skull consist of cranial and facial parts. there are 26 bones in the skull.
the bones of the trunk are the spinal column or the spine and the chest (ribs and the breastbone). the spine consists of the cervical, thoracic, lumbar and sacral vertebrae and the coccyx.
the vertebra is a small bone, which is formed by the body and the arches. all the vertebrae compose the spinal column or the spine. there are 32 or 34 vertebrae in the spine of the adult. in the spinal column there are seven cervical vertebrae, twelve thoracic vertebrae five lumbar, five sacral vertebrae and from one to five vertebrae which form the coccyx. the cervical part of the spine is formed by seven cervical vertebrae. twelve thoracic vertebrae have large bodies. the lumbar vertebrae are the largest vertebrae in the spinal column. they have oval bodies.
the chest (thorax) is composed of 12 thoracic vertebrae, the breastbone and 12 pairs of ribs. the breastbone is a long bone in the middle of the chest. it is composed of three main parts. the basic part of the chest is formed by the ribs. on each side of the chest seven ribs are connected with the breastbone by cartilages. the cartilages of three other ribs are connected with each other and with the seventh rib. but the cartilages of these ribs are not connected with the breastbone. the eleventh and the twelfth ribs are not connected with the breastbone either. they are not connected with other ribs, they are free. each rib is composed of a head, neck and body.
the lower extremity consists of the thigh, leg and foot. it is connected with the trunk by the pelvis. the upper extremity is formed by the arm, forearm and hand. it is connected with the trunk by the shoulder girdle.
the bones of the skeleton are connected together by the joints or by the cartilages and ligaments. the bones consist of organic and inorganic substance.
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