Corpus: Intercostales externi muscles

The intercostales externi muscles are part of the autochthonous pectoral musculature, forming the superficial layer of the intercostal muscles.

The intercostales externi muscles originate from the lower edge of the 1st to the 11th rib, extending from the costal tuberosity to the cartilage-bone junction. The external intercostal membrane, an aponeurosis, corresponds to the muscles between the costal cartilages. The muscle fibers run obliquely from the dorsal-cranial direction to the ventral-caudal direction, mirroring the fiber orientation of the obliquus externus abdominis muscle. These muscles insert along the upper edges of the 2nd to the 12th rib.

The intercostales externi muscles are innervated by the intercostal nerves 1-11.

As part of the respiratory musculature, the intercostales externi muscles support inspiration. When contracted, they tense the adjacent intercostal spaces, leading to an increase in the volume of the bony thorax, thus aiding in the process of breathing.