The external intercostals muscles are a group of muscles located between the ribs in the chest. They extend from the upper border of one rib to the lower border of the rib above it. The external intercostals muscles are innervated by the intercostal nerves.

The main function of the external intercostals muscles is to assist in the movement of the rib cage during respiration. When the external intercostals muscles contract, they lift the rib cage and increase the volume of the thoracic cavity. This helps to draw air into the lungs during inhalation. When the external intercostals muscles relax, they allow the rib cage to return to its resting position, which helps to exhale air from the lungs.

The external intercostals muscles are commonly used in activities that require breathing, such as talking, singing, and exercising. They are also used in activities that require lifting or moving the rib cage, such as coughing or sneezing.