respiratory muscles, the muscles that produce volume changes of the thorax during breathing. The inspiratory muscles include the hemidiaphragms, external intercostals, scaleni, sternomastoids, trapezius, pectoralis major, pectoralis minor, subclavius, latissimus dorsi, serratus anterior, and muscles that extend the back. The expiratory muscles are the internal intercostals, the abdominals, and the muscles that flex the back.
