Innermost Intercostal Muscle (Left) (Musculus intercostalis intimus)
Educational content only — not medical advice.
Anatomy
The incomplete innermost of the three layers, lying deep to the intercostal neurovascular bundle with the same fiber direction as the internal intercostal. It spans the middle part of the spaces only, crossing more than one intercostal space at a time, and belongs to the same plane as the transversus thoracis and subcostales.
Origin & insertion
From the lower border of each rib and its costal cartilage, to the upper border of the rib one or two levels below.
Action
Depresses the ribs in expiration and stiffens the inner chest wall.
Innervation
Intercostal nerves (T1–T11).
Clinical notes
It is the layer the chest-drain tract crosses last before the parietal pleura, and the plane that separates the neurovascular bundle from the lung — the reason an "inside-out" penetration above the rib still risks the vessels if the needle is driven too deeply.
Related structures
Educational references
FAQ
What is the role of the Innermost Intercostal Muscle (Left)?
The incomplete innermost of the three layers, lying deep to the intercostal neurovascular bundle with the same fiber direction as the internal intercostal. It spans the middle part of the spaces only, crossing more than one intercostal space at a time, and belongs to the same plane as the transversus thoracis and subcostales.
Why is the Innermost Intercostal Muscle (Left) clinically important?
It is the layer the chest-drain tract crosses last before the parietal pleura, and the plane that separates the neurovascular bundle from the lung — the reason an "inside-out" penetration above the rib still risks the vessels if the needle is driven too deeply.
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