Skeleton (anatomy), term applied to all the rigid or semirigid structures supporting the soft tissues of an animal's body and providing leverage for muscular action. In vertebrates, the skeleton is known as the endoskeleton and is formed within the body. Some invertebrate animals, such as insects and crustaceans, have skeletons known as exoskeletons on the outside of the body.

 The Structure and Functions of Bones

 Knowledge of the structure and function of bones and aspects of skeletal system generally are essential parts of training in many therapies, such as Massage, Aromatherapy, Acupuncture, Shiatsu, and others.


 Types of Bones

 There are axial and appendicular bones.
(The appendages are the arms and legs, which contain approx. 30 bones each.)

  There are typically 22 bones in the head.

  There are 33 bones in the spine.

 These include:

7 cervix (neck);
12 thorax;
5 lumbar;
5 sacral;
4 coccyx.

  The pelvic girdle is fused to the sacrum at the sacro-illiac joint. The pelvis is the part that is added onto the spine.

  The thorax (chest) consists of 12 pairs of ribs: 7 pairs 'true' ribs (joined directly to the sternum ("breast-bone"));
3 pairs 'false' ribs (joined to the sternum ("breast-bone") by cartilage);
2 pairs 'floating' ribs (not connected to the sternum ("breast-bone");

  The shoulder girdle consists of the scapula (shoulder blade) and the clavicle ("collar bone").

 The following table summarises the five main categories of bones, together with another category (sutural bones).

 Diagram illustrating the general structure of long bones:


 Bones grow from their ends (extremities). Under normal circumstances bones stop growing when the owner reaches his.her late teens or early twenties. Bone marrow produces stem cells, such as erythrocytes (red blood cells) and leucocytes (white blood cells).

 Definitions of main types of bone tissue:

 Compact tissue forms the outer shell of bones. It consists of a very hard (virtually solid) mass of bony tissue arranged in concentric layers (Haversian systems).

 Cancellous tissue is located beneath the compact bone and consists of a meshwork of bony bars (trabeculae) with many interconnecting spaces containing bone marrow.

 The diagram above labels the basic components of a typical long bone: articulartory cartilage; spongy bone; bone marrow; endosteum; compact bone; periosteum; medullary cavity, and a blood vessel (indicating blood supply and circulation within bones).

 Articulatory (or articular) cartilage reduces friction and absorbs shock at freely moveable joints.
 Endosteum is the membrane that lines the cavity of a bones.
 Periosteum is a tough fibrous membrane that surrounds the outside of bones wherever they are not covered by articulatory cartilage.
 In adults the medullary cavity contains fatty yellow bone marrow.