Innermost intercostal muscles

Dr Craig Hacking et al.

The innermost intercostal muscles are muscles of respiration. They are the deepest intercostal muscles located in the intercostal spaces, and contract along with the internal intercostal muscles to reduce the transverse dimension of the thoracic cavity during expiration.

The innermost intercostal muscles are the most deep muscle of the three intercostal muscles and arise from the inner margin of the costal groove of the rib above. The fibres run in a downwards, backwards and lateral (like the internal intercostal muscles and perpendicular to the external intercostal muscles) and insert into the superior border of the rib below. Some authors describe the muscle continuing over several ribs and intercostal spaces, as opposed to the internal and external intercostal muscles which only span each intercostal space 1.

As their name indicates, they are internal to the internal and external intercostal muscles. Variably, the muscles become continuous anteriorly with the subcostal muscles and posteriorly with the tranversus thoracis muscles

Muscular branches from the intercostal nerves of the respective intercostal space (T1-T11), which run with the intercostal vessels under the costal groove in between the internal and innermost intercostal muscles.

Internal intercostal muscle contraction causes reduction in volume of the of the thoracic cavity in the transverse dimension, expelling air from the lungs during inspiration. They are probably the weakest of the intercostal muscles.


Thoracic anatomy
Share article

Article Information

rID: 37731
Section: Anatomy
Tag: anatomy
Synonyms or Alternate Spellings:

Support Radiopaedia and see fewer ads

Cases and Figures

  • Drag
    Figure 1: Intercostal space
    Drag here to reorder.
  • Updating… Please wait.
    Loadinganimation

    Alert accept

    Error Unable to process the form. Check for errors and try again.

    Alert accept Thank you for updating your details.