External intercostal muscles

Intercostales externi muscle
Deep muscles of the chest and front of the arm, with the boundaries of the axilla. (Intercostalis externus labeled at bottom center.)
The Obliquus internus abdominis. (Intercostalis externus labeled at top center.)
Latin	musculi intercostales externi
Gray's	subject #117 403
Origin	lower border of ribs
Insertion	upper border of rib below
Artery	intercostal arteries
Nerve	intercostal nerves
Actions	Inhalation
Antagonist	intercostales interni muscles

The Intercostales externi (External intercostals) are eleven in number on either side.

They extend from the tubercles of the ribs behind, to the cartilages of the ribs in front, where they end in thin membranes, the anterior intercostal membranes , which are continued forward to the sternum.

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 Intercostales interni, and their fibers are directed obliquely downward and laterally on the back of the thorax, and downward, forward, and medially on the front (the example is often used of sticking one's hands in their pocket and noting the direction of the fingers pointing downward and medially).

Variations

Continuation with the Obliquus externus or Serratus anterior: A Supracostalis muscle, from the anterior end of the first rib down to the second, third or fourth ribs occasionally occurs.

Additional images

• 

  A central rib of the left side. Inferior aspect.

• 

  Diagram of the course and branches of a typical intercostal nerve.

External links

• LUC exin
• -556793779 at GPnotebook
• External+intercostal+muscle at eMedicine Dictionary

This article was originally based on an entry from a public domain edition of Gray's Anatomy. As such, some of the information contained within it may be outdated.