"Muscular branches from the intercostal nerves of the respective intercostal space (T1-T11), which run with the intercostal vessels under the costal groove in between the internal and innermost intercostal muscles."
Expected headings
"Blood supply"
"Action"
"The external intercostal muscles are the outermost muscle of the three intercostal muscles and arise from the lower border of the rib above the respective intercostal space. The fibres run in a downwards, forwards and medial direction and insert into the outer lip of the superior border of the rib below. At their insertion they end in thin anterior intercostal membranes that continue towards the sternum. Anteriorly the lower muscles become continuous with the external oblique muscles in the anterolateral abdominal wall. As their name indicates, they are external to the internal intercostal muscles."