Girish Mahajan (Editor)

External intercostal muscles

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Origin
  
Lower border of ribs

Nerve
  
intercostal nerves

Artery
  
intercostal arteries

Actions
  
Inhalation

External intercostal muscles

Insertion
  
Upper border of rib below

Antagonist
  
intercostales interni muscles

The external intercostal muscles, or external intercostals (Intercostales externi) are eleven in number on either side.

Contents

Structure

The muscles extend from the tubercles of the ribs behind, to the cartilages of the ribs in front, where they end in thin membranes, the external intercostal membranes, which are continued forward to the sternum. These muscles work in unison when inhalation occurs. The internal intercostal muscles relax while the external muscles contract causing the expansion of the chest cavity and an influx of air into the lungs.

Each arises from the lower border of a rib, and is inserted into the upper border of the rib below. In the two lower spaces they extend to the ends of the cartilages, and in the upper two or three spaces they do not quite reach the ends of the ribs.

They are thicker than the internal intercostals, and their fibers are directed obliquely downward and laterally on the back of the thorax, and downward, forward, and medially on the front and are very important

Variations

Continuation with the external oblique or serratus anterior: A supracostalis muscle, from the anterior end of the first rib down to the second, third or fourth ribs occasionally occurs.

  • Inhalation
  • References

    External intercostal muscles Wikipedia