intercostalis

Intercostalis is a term used in anatomy to describe the muscles between the ribs, collectively known as the intercostal muscles (musculi intercostales). The three principal layers are the external intercostal muscles (musculi intercostales externi), the internal intercostal muscles (musculi intercostales interni), and the innermost intercostal muscles (musculi intercostales intimus).

The external intercostals run obliquely downward and anteriorly from rib to rib and elevate the ribs during inspiration. The internal intercostals run downward and posteriorly and act mainly to depress the ribs during expiration; the innermost intercostals lie deep to the internal intercostals and have a similar function. The intercostal muscles are supported by intercostal membranes and contribute to the stability and movement of the thoracic cage during breathing.

Innervation is provided by the intercostal nerves, which are the ventral rami of the thoracic spinal nerves (primarily T1–T11; T12 is supplied by the subcostal nerve). Blood supply comes from the posterior intercostal arteries (branches of the aorta) and the anterior intercostal arteries (branches of the internal thoracic arteries); venous drainage mirrors the arterial pattern.

Clinically, intercostal nerves can be targeted for analgesia via intercostal nerve blocks, commonly used after thoracic surgery or rib fractures. Injury, inflammation, or surgical intervention affecting the intercostal muscles can influence chest wall movement and overall ventilation. The term intercostalis thus denotes the muscular structure between the ribs essential for respiration and thoracic stability.