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, as well as the major blood vessels rest in the protective frame of the rib cage.

The thoracic cage is formed by the following structures: 

• Anteriorly - sternum (Read more!);
• Laterally - twelve pairs of ribs (Read more!) and their respective costal cartilages; 
• Posteriorly - twelve thoracic vertebrae (Read more!) 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 the ribs and function as accessory respiratory muscles, and some of them also stabilize the positions of the first and last ribs.