Muscle
Internal intercostals
Depress ribs (expiration)
High-yield
Fibres perpendicular to external intercostals; depress ribs in forced expiration. Intercostal nerves.
Overview
Muscles deep to the external intercostals whose fibres run perpendicularly; their interosseous parts depress the ribs during forced expiration.
Reference facts
- Origin
Superior border of the rib below (medial to the costal angle)
- Insertion
Inferior border of the rib above
- Action
Depress the ribs in forced expiration; the interchondral part aids inspiration
- Innervation
Intercostal nerves (anterior rami of T1–T11)
- Blood supply
Posterior and anterior intercostal arteries