External intercostal muscles

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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
Artery: intercostal arteries
Nerve: intercostal nerves
Action: Inhalation
Antagonist: intercostales interni muscles
Dorlands/Elsevier m_22/12549368


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 lateralward on the back of the thorax, and downward, forward, and medialward on the front.


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.

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This article was originally based on an entry from a public domain edition of Gray's Anatomy. As such, some of the information contained herein may be outdated. Please edit the article if this is the case, and feel free to remove this notice when it is no longer relevant.

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