Thorax

The thoracic cage includes the thoracic vertebrae, sternum, ribs, and costal cartilages (see Figure 1 ). The sternum (breastbone) consists of three fused bones: the manubrium, body, and xiphoid process. There are 12 pairs of ribs, all of which attach to their posterior ends to vertebrae. At their anterior ends, they differ as to how they attach, as follows:

• Seven pairs of true ribs (vertebrosternal ribs) attach directly to the sternum with hyaline cartilage called costal cartilage.
  
  

  Figure 1 The thoracic cage.

• Three pairs of false ribs (vertebrochondral ribs) do not attach to the sternum. Rather, they connect (with costal cartilage) to the rib directly above them.

• Two pairs of false ribs (floating ribs or vertebral ribs) do not attach to anything at their anterior ends.

Here are important features of a rib:

• The head is the end of the rib that articulates with the vertebral column.

• The superior and inferior facets are facets on the head that articulate with the facets of the thoracic vertebrae.

• The neck, just beyond the head, bears a tubercle (rounded process) that articulates with the facet of the vertebral transverse process. Part of the tubercle also presents a place of attachment for ligaments.

• The costal angle designates the sharp turn of the rib.

• The costal groove, a passageway on the inside of the bending rib, provides for blood vessels and intercostals nerves.

• The body (shaft) is the major part of the rib- that part beyond the costal angle.

• Intercostal spaces, the areas between the ribs, are occupied by the intercostal muscles.

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