Expansion
External intercostals run downwards and forwards, like hands in pockets
Expansion
Put your hands in your pockets, your fingers point downwards and forwards, in the direction of the external intercostal fibres.
- External intercostal - downwards and forwards, active in inspiration
- Internal intercostal - downwards and backwards, at right angles to the external
- Innermost intercostal - same direction as the internal, separated from it by the neurovascular bundle
The neurovascular bundle lying between the internal and innermost layers is the reason a needle passed close to the lower border of a rib can injure the intercostal vessels and nerve.