External Intercostal Muscle (Musculus intercostalis externus)
Educational content only — not medical advice.
Anatomy
The outermost of the three intercostal layers, its fibres running downward and forward from the rib above to the rib below — the same oblique direction as the external oblique of the abdomen. It is complete posteriorly but continues anteriorly to the costochondral junction only as the external intercostal membrane.
Origin & insertion
From the lower border of each rib and its costal cartilage, to the upper border of the rib below.
Action
Elevates the ribs and, with the other intercostals, stiffens the intercostal space against the pressure swings of breathing.
Innervation
Intercostal nerves (T1–T11).
Clinical notes
The intercostal neurovascular bundle runs in the costal groove below each rib, so a chest drain or thoracocentesis needle is introduced just ABOVE the lower rib of the space — the classic procedure-linked teaching point of this muscle plane.
Related structures
Educational references
FAQ
What is the role of the External Intercostal Muscle?
The outermost of the three intercostal layers, its fibres running downward and forward from the rib above to the rib below — the same oblique direction as the external oblique of the abdomen. It is complete posteriorly but continues anteriorly to the costochondral junction only as the external intercostal membrane.
Why is the External Intercostal Muscle clinically important?
The intercostal neurovascular bundle runs in the costal groove below each rib, so a chest drain or thoracocentesis needle is introduced just ABOVE the lower rib of the space — the classic procedure-linked teaching point of this muscle plane.
Source & license
BodyParts3D, © The Database Center for Life Science licensed under CC Attribution 4.0 International (https://creativecommons.org/licenses/by/4.0/). license details