Quick Facts
Origin: Inferior borders and internal surfaces of first to eleventh ribs.
Insertion: Superior borders and internal surfaces of ribs immediately below origin sites.
Action: Elevates ribs at their costovertebral joints.
Innervation: Adjacent intercostal nerves (anterior rami of thoracic nerves).
Arterial Supply: Posterior intercostal arteries, collateral branches of posterior intercostal arteries, anterior intercostal branches of internal thoracic artery, and musculophrenic artery.
Origin
The innermost intercostal muscles originate from the inferior borders and internal surfaces of the first to eleventh ribs.
Insertion
The fibers of the innermost intercostal muscles travel obliquely, in the same direction as the internal intercostal muscles and the opposite direction of the external intercostal muscles, where:
- the fibers on the lateral aspect of the thorax travel posteroinferiorly;
- the fibers on the anterior aspect of the thorax travel inferolaterally.
The innermost intercostal muscles insert onto the superior border and internal surface of the rib that is immediately below its origin site (i.e., the superior borders and internal surfaces of the second to twelfth ribs).
Key Features & Anatomical Relations
The innermost intercostal muscles are the inner of the three intercostal muscles in the thorax, the other two being the external and internal intercostals. They consist of eleven pairs of flat skeletal muscles; however, they may be absent in the superior thoracic region in some individuals.
The innermost intercostal muscles are found within the middle two quarters of the intercostal spaces. They are located:
- superficial to the endothoracic fascia and parietal pleura;
- deep to the internal intercostal muscles, the anterior rami of thoracic nerves (intercostal nerves), and the intercostal vessels.
Actions
The innermost intercostal muscles elevate the ribs at their costovertebral joints (Netter, 2011).
References
Netter, F. H. (2011) Atlas of Human Anatomy. Netter Basic Science Series: Saunders/Elsevier.
Actions
The innermost intercostal muscles elevate the ribs at their costovertebral joints (Netter, 2011).
