External intercostal muscles

The external intercostal muscles, or external intercostals (Intercostales externi) are eleven in number on both sides.Position of the external intercostal muscles (shown in red). Animation.Deep muscles of the chest and front of the arm, with the boundaries of the axilla. (Intercostalis externus labeled at bottom center.)A central rib of the left side. Inferior aspect.Diagram of the course and branches of a typical intercostal nerve. The external intercostal muscles, or external intercostals (Intercostales externi) are eleven in number on both sides. The muscles extend from the tubercles of the ribs behind, to the cartilages of the ribs in front, where they end in thin membranes, the external intercostal membranes, which are continued forward to the sternum.These muscles work in unison when inhalation occurs. The internal intercostal muscles relax while the external muscles contract causing the expansion of the chest cavity and an influx of air into the lungs.