Bones and joints of thorax

Bones and joints of thorax
The thorax is an osseocartilaginous cavity or cage for various viscera, providing them due support and protection. This cage is not static, but dynamic, as it moves at its various joints, increasing or decreasing the various diameters of the cavity for an extremely important process of respiration, which is life for all of us.
BONES OF THE THORAX
 
THE RIBS OR COSTAE
1. There are 12 ribs on each side forming the greater part of the thoracic skeleton. The number may be increased by development of a cervical or a lumbar rib; or the number may be reduced to 11 by the absence of the twelfth rib. 
2. The ribs are bony arches arranged one below the other . The gaps between the ribs are  called intercostal spaces. The spaces are deeper in front than behind, and deeper between the upper than between the lower ribs. 
3. The ribs are placed obliquely, the upper ribs being less oblique than the lower. The obliquity reaches its maximum at the ninth rib, and thereafter it gradually decreases to the twelfth rib.
4. The length of the ribs increases from the first to the seventh ribs, and then gradually decreases from the eighth to twelfth ribs. 
5. The breadth of the ribs decreases from above downwards. In the upper ten ribs, the anterior ends are broader than the posterior ends. 
6. The first 7 fibs which are connected through itheir cartilages to the sternum are called true ribs, or vertebrosternal fibs. The remaining five are false ribs. Out of these the cartilages of the eighth, ninth and tenth ribs are joined to the next higher cartilage and are known as vertebrochondral ribs. The anterior ends of the eleventh and twelfth ribs are free and are called floating ribs or vertebral ribs. 
7. The first two and last three ribs have special features, and are atypical ribs. The third to ninth ribs are typical ribs.
Typical Ribs
 Side determination 
1. The anterior end bears a concave depression. The posterior end bears a head, a neck and a tubercle. 
2. The shaft is convex outwards and there is costal groove situated along the lower part of its inner surface, so that the lower border is thin and the upper border rounded.

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