The thoracic wall surrounds the thoracic cavity, which is the anatomical region where viscera like the heart and lungs can be found.

The thoracic wall contains a variety of muscles, where many of the muscles that cover and attach to the thoracic wall have a primary action elsewhere, such as the arms, neck, and abdomen, and it is their secondary actions that affect the movements of the thoracic wall.

For example, the pectoralis major and pectoralis minor muscles overlay the thoracic wall but they are primarily involved with movements of the upper limb and their secondary action is to act on the thoracic wall as accessory muscles of respiration.

However, the thoracic wall also does have muscles that have their primary action in the thoracic wall, and these are called the true muscles. They are the serratus posterior, levatores costarum, subcostals, transversus thoracis, and the innermost, internal, and external intercostals.

Let’s start with the two serratus posterior muscles. There’s a serratus posterior superior muscle and serratus posterior inferior muscle on each side. The Serratus posterior superior muscles have their proximal attachment at the nuchal ligament and the spinous processes of C7 through T3 vertebrae and their distal attachment at the superior borders of the 2nd through 5th ribs. Its main action is the elevation of the superior 4 ribs during inspiration.

The serratus posterior inferior muscles have their proximal attachment at the spinous processes of T11 through L2 vertebrae and their distal attachment at the inferior borders of 9th through 12th ribs near their angles. Its main action is depressing the inferior ribs in order to prevent them from being pulled upwards by the diaphragm.

Both of these muscles have also been shown to have a role in proprioception, meaning that they might make you aware of the position of the body. For example, when you’re lying in bed with your eyes closed, these muscles, among others, could send signals to the brain regarding where you are and what’s your position in relation to the bed.

Next, the levatores costarum muscles are 12 triangle shaped muscles with a proximal attachment to the transverse processes of C7 through T11 vertebrae and distal attachments to the subjacent ribs between the tubercle and the angle of that rib. Their main action is to elevate the ribs.