Muscles of the Thoracic Wall

The muscles of the thorax consist of the intercostals and diaphragm. The intercostal muscles are arranged as three layers (external layer, internal layer and an incomplete innermost layer) between the ribs. The diaphragm closes the thoracic outlet and separates the thoracic cavity from the abdominal cavity. The three layers of the intercostal muscles are:

The diaphragm is the most important muscle of the thoracic wall. During normal respiration, this muscle is the primary component.

As you can see, the innermost layer is split into three differently named muscle groups. The transversus thoracis, innermost intercostal and subcostal muscles make up the deepest layer of muscles from anterior to posterior, respectively.

  • external intercostal
  • internal intercostal
  • innermost intercostal
  • transversus thoracis
  • subcostal
external intercostal muscle internal intercostal muscle innermost intercostal muscle
transverse thoracis muscle subcostal muscles diaphragm as seen
from below

Details of the diaphragm will be considered later when the abdomen is examined. We are presently interested in the thoracic surface or the dome of the diaphragm.

Bones of the Thorax Nerves & Vessels of Thoracic Wall

Table of Contents for Thorax
Practice Examination