The thoracic cage (also known as the rib cage) is a bony framework of the thoracic wall. It encloses the thoracic cavity and is composed of various bones, cartilages and joints. 

The shape of the thoracic cage resembles a domed birdcage. Internal organs such as the heart, lungs, spleen and liver, and major blood vessels rest in the protective frame of the rib cage.

The thoracic cage is formed by: 

• Anteriorly - sternum (it is also known as the breastbone);
•  Laterally - twelve pairs of ribs and their respective costal cartilages; all rib pairs can be subdivided into three groups depending on their attachment sites: 
  • True ribs (7)- attach directly to the sternum;
  • False ribs (3) - attach indirectly to the sternum via costal cartilages of the ribs above them;
  • Floating ribs (2) - do not attach directly or indirectly to the sternum;
• Posteriorly - twelve thoracic vertebrae and their respective intervertebral discs.

The skeletal framework of the chest wall provides a rich amount of attachment sites for muscles of the neck, abdomen, back and upper limbs. Some of these muscles attach to ribs and function as accessory respiratory muscles, and some of them also stabilize the positions of the first and last ribs.