The Musculus intercostalis internus, is a seletal muscle which runs in each space between the rips of the thorax. The Musculi intercostales interni (Plural) therefore run oblique dorsokaudal (back-tailward, in humans from back downward) from one rip to the subsequent one. The Fascia, which covers the muscle dorsally, is the so called Fascia thoracica interna.

Thoracic Spine (TS)

Intercostalis Interni

Origin
Rip
Projection
next Rippe
Function
Ausatmung
Innervation
Nervi intercostales (Spinalnerven des Brustteils of the spinal marrow)
Spinal Segments
Th1-Th11

The Musculi intercostales interni together with the rips and the overlieng liegenden Musculi intercostales externi form the chest wall. The contraction of the Musculi intercostales interni lowers the rips and tightens the ribcage, by which these muscles support the Exhalation (Exspiration) („helping exspirator“) and are considered the breathing musculature.