Muscle of expiration: (A) External intercostal, (B) Diaphragm, (C) Internal intercostal, (D) Serratus anterior
Answer is C. MUSCLE OF INSPIRATION: Quiet: Diaphragm External intercostals Interchondral pa of internal intercostal of contralateral side. Deep: Erector spinae Scalene muscles Pectoral muscles Serratus anterior MUSCLE OF EXPIRATION: Quiet: Passive process d/o inherent quality of lungs Forced: Muscles of anterior abdominal wall with internal intercostal (except interchondral pa)