Internal Intercostals

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

By TeachMeSeries Ltd (2025)

Fig 1
The external and internal intercostals of the thoracic wall.