Name

# External Intercostals

Pronunciation

(in-ter-KOS-talz)

Origin/Proximal Attachment

Inferior border of an upper rib

Insertion/Distal Attachment

Superior border of a rib below (External muscle fibres run obliquely & anteriorly, inserting toward the costal cartilage)

Action/Relevance

Elevates the ribs in inspiration (superior ribs fixed) May depress the ribs in forced expiration (inferior ribs fixed)

Innervation

Intercostal nerves

Notes

The external intercostal muscles are the most superficial of all the intercostals. Within each intercostal space, they arise from the inferior border of the rib that lies superiorly. The muscle fibres pass obliquely down and inferiorly to insert into the superior border of the immediately inferior rib.

Each intercostal is muscular from the costal tubercle of each rib posteriorly but becomes membranous at the each respective costochondral junction anteriorly.

The external intercostals are supplied by collateral branches of the first to eleventh intercostal nerves.