Anatomy of the Muscles of the Thoracic Region

Muscles of the Thoracic Region - Listed Alphabetically
Muscle	Origin	Insertion	Action	Innervation	Artery	Notes
diaphragm	xiphoid process, costal margin, fascia over the quadratus lumborum and psoas major mm.(lateral & medial arcuate ligaments), vertebral bodies L1-L3	central tendon of the diaphragm	pushes the abdominal viscera inferiorly, increasing the volume of the thoracic cavity (inspiration)	phrenic nerve (C3-C5)	musculophrenic a., superior phrenic a., inferior phrenic a.	left crus attaches to the L1-L2 vertebral bodies, the right crus attaches to the L1-L3 vertebral bodies
external intercostal	lower border of a rib within an intercostal space	upper border of the rib below, coursing, downward and medially	keeps the intercostal space from blowing out or sucking in during respiration	intercostal nerves (T1-T11)	intercostal a.	11 in number; they extend from the tubercle of the rib to the costochondral junction; continuous with the external intercostal membrane anteriorly
innermost intercostal	upper borders of a rib	fibers course up and medially to insert on the inferior margin of the rib above	keeps the intercostal space from blowing out or sucking in during respiration	intercostal nerves (T1-T11)	intercostal a.	innermost intercostal mm. have the same fiber direction as the internal intercostal mm., the only difference being that they lie deep to the intercostal neurovascular bundle
internal intercostal	upper border of a rib	lower border of rib above, coursing up and medially	keeps the intercostal space from blowing out or sucking in during respiration	intercostal nerves (T1-T11)	intercostal a.	11 in number; they extend from the margin of the sternum to the angle of the rib; continuous posteriorly with the internal intercostal membrane
levatores costarum	transverse processes C7-T11	rib below its origin, medial to the angle	elevates the rib	dorsal primary rami of spinal nerves C7-T11	deep cervical a., intercostal aa.	these are fairly small and insignificant muscles
subcostalis	angle of ribs	angle of a rib 2-3 ribs above origin	compresses the intercostal spaces	intercostal nerves	intercostal a.	subcostalis, transversus thoracis & innermost intercostal mm. make up the deepest intercostal muscle layer
transversus thoracis	posterior surface of the sternum	inner surfaces of costal cartilages 2-6	compresses the thorax for forced expiration	intercostal nerves 2-6	internal thoracic a.	transversus thoracis, subcostalis & innermost intercostal mm. make up the innermost intercostal muscle layer