Innermost intercostal muscle

The innermost intercostal muscle is a layer of intercostal muscles.^[1] It may also be called the intima of the internal intercostal muscles.^[2] It is the deepest muscular layer of the thorax,^[3] with muscle fibres running vertically (in parallel with the internal intercostal muscles).^[2] It is present only in the middle of each intercostal space, and often not present higher up the rib cage.^[3] It lies deep to the plane that contains the intercostal nerves and intercostal vessels, and the internal intercostal muscles.^[3][4] The diaphragm is continuous with the innermost intercostal muscle.^[5]

Innermost intercostal muscle
Innermost intercostal muscle (red), seen from back.
Details
Origin	Infero-posterior border of each rib (above)
Insertion	Supero-posterior border of the rib (below)
Artery	Intercostal arteries
Nerve	Intercostal nerves
Actions	Through adduction of upper ribs to the lower ribs the muscles narrow intercostal slits and diminish thorax volume, therefore the muscles represent expiratory muscles.
Identifiers
Latin	musculus intercostalis intimus
TA98	A04.4.01.014
TA2	2313
FMA	74086
Anatomical terms of muscle [edit on Wikidata]

Additional images

• 
  Innermost intercostal muscle (shown in red). Animation.
• 
  A cutout of the thoracic wall showing the three layers of intercostal muscle - from the left wall.