Subcostal muscles

The subcostal muscles are thin muscular slips or fasciculi which are located on the inner surface of the posterior thoracic wall. They are part of the deepest layer of thoracic wall muscles and lie in the same plane as the innermost intercostal muscles and transverse thoracis muscles, and are closely related to the parietal pleura.

Attachments

• Origin: Arise from the internal surface of a rib near its angle.

• Insertion: The fasciculi span more than one intercostal pace and insert onto the internal surface of the second or third rib below.

Fibre Direction

• Fibres run in the same direction as the internal intercostal muscles, i.e. infero-posteriorly (downwards and backwards).

Nerve Supply

• Supplied by the corresponding intercostal nerves.

Blood Supply

• Supplied by posterior intercostal arteries, and also by branches of anterior intercostal arteries

Functions

• Assist in forced expiration by depressing the ribs.

• Help stabilise the thoracic wall during respiration.