The external intercostals are a muscle of the thoracic wall. They are the most superficial of the intercostal muscles.
Their fibres are orientated in an inferior and anterior direction.
- Attachments: Originates at the lower border of each rib, inserting onto the superior border of the rib below.
- Actions: Elevates the ribs and increases the thoracic volume during inspiration.
- Innervation: Intercostal nerves (T1-T11).
- Blood supply: Anterior and posterior intercostal arteries.