The internal intercostals are a muscle of the thoracic wall. They lie deep to the external intercostal muscles.
Their fibres are orientated in an inferior and posterior direction.
- Attachments: Originates from the lateral edge of the costal groove and inserts onto the superior surface of the rib below.
- Actions: Stablises the position of the ribs during normal respiration. Depresses the ribs and decreases the thoracic volume during forced expiration.
- Innervation: Intercostal nerves (T1-T11).
- Blood supply: Anterior and posterior intercostal arteries
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