Author: Dr Peter de Souza
Last modified: 14 December 2021


This is a tutorial on the thoracic wall. The thorax extends from the superior thoracic aperture to the inferior thoracic aperture. It's comprised of this bony skeletal framework, which protects the cavity and the vital structures within it.


We’ll just take a look at the opening to the thorax first. This superior thoracic aperture is formed at the back by the body of the 1st thoracic vertebra. And then, the lateral borders of the thoracic aperture are formed by the medial margin of this 1st rib, which I'm outlining here. And then anteriorly, we've got the manubrium of the sternum and it forms this nice ring, this aperture or opening into the thorax.

Structures that enter and exit the thorax enter and exit through this aperture. You've got structures coming from the head and the neck and you've got structures going to and fro the upper limbs.


The inferior thoracic aperture at the bottom of the thorax is formed by the – we've got the costal margin anteriorly. And then laterally, we've got the distal tip of the 11th rib. And then you've got the 12th rib and posteriorly, you've got the body of T12. This forms the outlet for the thorax and it's actually closed off by the diaphragm.


You’ve got the body of the 12th thoracic vertebra at the back. And then posteriorly and laterally, we've got the whole of rib 12 and the distal part of rib 11, the end of rib 11. And then we've got the costal margin formed by these costal cartilages anteriorly and laterally. And then, right anteriorly, you've got the xiphoid process.


You can see how the inferior thoracic aperture is actually closed off by the diaphragm muscle.  Structures that pass from the thoracic into abdominal cavity pass through the diaphragm or they pass behind the diaphragm.  You’ve got structures like the aorta and the inferior vena cava as well as the oesophagus, which pass through the diaphragm.


In terms of the bony framework which makes up the thorax, you've got the 12th thoracic vertebra at the back, which make up the posterior part of the thorax. And then you've got the ribs which form the lateral part.  You’ve got 12 ribs which articulate with the 12th thoracic vertebra forming the lateral walls of the thorax. And then anteriorly, these ribs articulate via a costal cartilage with the sternum.  You’ve got these three elements to the sternum. You've got the manubrium of the sternum, the body of the sternum and you've got the little xiphoid process at the end.


Within the thorax itself, you've got three cavities. You've got two pleural cavities, which contain the lungs and they sit laterally.  I'm just drawing this on in red.  You’ve got two pleural cavities containing the lungs in the thorax. And in between these two pleural cavities, you've got the mediastinum, which contains the heart and the great vessels as well as other structures like the trachea and oesophagus, various nerves and other lymphatic structures.


The thoracic wall is this musculoskeletal framework which can protect the vital structures that lie within it within these three cavities.


Just to mention about the ribcage, you've got 12 ribs which articulate with the 12 thoracic vertebrae. You've got seven true ribs and five false ribs.  The top seven ribs are called 'true' ribs because you can see this costal cartilage which sits at the end of the rib and articulates with the sternum.  The top seven ribs have this costal cartilage articulation with the sternum.


And then you've got the five ribs below, ribs 8-12, which are false ribs.  The bottom two ribs are actually called floating ribs because they don’t have any costal cartilage, they’re essentially floating, which gives rise to the name.


And then you've got ribs 8-10, which do have a costal cartilage because these costal cartilages actually articulate with the inferior cartilage of the cartilage above.  They don’t have independent articulations with the sternum.  These are all called false ribs.


The top seven are true ribs, the bottom five are false ribs and the bottom two are floating ribs.


That’s the skeletal framework of the thoracic wall.