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The Skeleton
The skeleton is composed of bones. In the adult the skeleton has over 200 bones.
The main part of the head and face is called the skull. The skull is composed of twenty-six bones. These bones form two basic parts of the skull, that is facial and cranial parts.
The bones of the skull are connected with the first cervical vertebra. The bones of the skull are connected together so firmly that it is very difficult to separate them.
The bones of the skull form one large cavity and some smaller cavities. The large cavity is called the cranial cavity. The brain is in the cranial cavity. One of the smaller cavities is the cavity of the nose. The other two cavities are the orbits. The eyeballs are in the orbits.
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 (также). 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.
There are three types of muscles in the body: striated muscles (1), also called voluntary or skeletal muscles, are the muscles fibers which move all bones, as well as the face and eyes. We have conscious control over the activity of this type of muscle.
Smooth muscles (2), also called involuntary or visceral muscles, are those muscles fibers which move our internal organs such as the digestive tract, blood vessels, and secretory ducts leading from glands. We have no conscious control over these muscles.
Cardiac muscle (3) is striated in appearance but like smooth muscle in its action. Its movement cannot be consciously controlled.




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