The Muscles of the Thoracic Cage - Podcast Version 0:00 / 0:00 1x 0.25x 0.5x 0.75x 1x 1.25x 1.5x 1.75x 2x The thoracic wall forms the anterior, posterior and lateral boundaries of the thorax. It is comprised of the five muscles, which act to change the volume of the thoracic cavity during respiration. External, internal and innermost intercostals Subcostals Transversus thoracis There are additional muscles that do not form the thoracic wall, but attach to it. These are termed accessory muscles of respiration and include the pectoralis major, minor, serratus anterior and the scalene muscles. In this article, we shall look at the anatomy of the muscles of the thoracic wall – their attachments, actions and innervation. Pro Feature - 3D Model You've Discovered a Pro Feature Access our 3D Model Library Explore, cut, dissect, annotate and manipulate our 3D models to visualise anatomy in a dynamic, interactive way. Learn More Intercostals The intercostal muscles lie in the intercostal spaces between ribs. They are organised into three layers. External Intercostals There are 11 pairs of external intercostal muscles. They run inferoanteriorly from the rib above to the rib below, and are continuous with the external oblique of the abdomen. Attachments: Originates at the lower border of each rib, inserting onto the superior border of the rib below. Actions: Stablises the position of the ribs during normal respiration. Elevates the ribs and increases the thoracic volume during forced inspiration. Innervation: Intercostal nerves (T1-T11). By TeachMeSeries Ltd (2026) Fig 1The external and internal intercostals of the thoracic wall. Internal Intercostals The internal intercostals lie deep to the external intercostals. They extend from the rib above to the one below, but in an opposite direction to the external intercostals (inferoposteriorly). They are continuous with the internal oblique muscle of the abdominal wall. Attachments: Originates from the lateral edge of the costal groove and inserts onto the superior surface of the rib below. Actions: Stablises the position of the ribs during normal respiration. Depresses the ribs and decreases the thoracic volume during forced expiration. Innervation: Intercostal nerves (T1-T11). Innermost Intercostals The innermost intercostals are the deepest of the intercostal muscles and are similar in structure to the internal intercostals. They are separated from the internal intercostals by the intercostal neurovascular bundle. They are found in the most lateral portion of the intercostal spaces. Attachments: Originates from the medial edge of the costal groove and inserts into the superior surface of the rib below. Actions: Stablises the position of the ribs during normal respiration. Depresses the ribs and decreases the thoracic volume during forced expiration. Innervation: Intercostal nerves (T1-T11) Pro Feature - Dissection Atlas Prosection of the muscles of the thoracic wall. Prosection of the muscles of the thoracic wall. You've Discovered a Pro Feature Access our Dissection Image Library Enhance your understanding with high-resolution dissection images showcasing real-life anatomy. Learn More Transversus Thoracis The transversus thoracis is located on the internal surface of the thoracic wall and is continuous with the transversus abdominis inferiorly. Attachments: Arises from the posterior surface of the inferior sternum and costal cartilage of the lower ribs. The fibres ascend and attach onto the internal surface of costal cartilages 2-6. Actions: Weak depressor of the ribs during expiration. Innervation: Intercostal nerves (T2-T6). By TeachMeSeries Ltd (2026) Fig 2View of the internal aspect of the thoracic wall. The internal intercostal and transverse thoracis muscles are visible. Subcostales The subcostal muscles are most developed in the inferior portion of the thoracic wall. The direction of the fibres is similar to that of the innermost intercostal muscles. Attachments: Originates from the inferior surface of the lower ribs. Attaches to the superior border of the second or third rib below. Actions: Stablises the position of the ribs during normal respiration. Depresses the ribs and decreases the thoracic volume during forced expiration. Innervation: Intercostal nerves. Do you think you’re ready? Take the quiz below Pro Feature - Quiz The Muscles of the Thoracic Cage Question 1 of 3 Submitting... Skip Next Rate question: You scored 0% Skipped: 0/3 1800 More Questions Available Upgrade to TeachMeAnatomy Pro Challenge yourself with over 1800 multiple-choice questions to reinforce learning Learn More Frequent questions What are the main muscles involved in the thoracic wall? The thoracic wall consists of five primary muscles: the external intercostals, internal intercostals, innermost intercostals, subcostals, and transversus thoracis. These muscles facilitate changes in thoracic cavity volume during respiration. How do the external intercostal muscles function during respiration? The external intercostal muscles elevate the ribs and increase thoracic volume during forced inspiration. They stabilise rib positions during normal breathing and are innervated by the intercostal nerves (T1-T11). What role do the internal intercostal muscles play in breathing? The internal intercostal muscles depress the ribs and reduce thoracic volume during forced expiration. They also help stabilise rib positions during normal respiration and are innervated by the intercostal nerves (T1-T11). Where do the subcostal muscles originate and what is their function? The subcostal muscles originate from the inferior surface of the lower ribs and attach to the superior border of the second or third rib below. They stabilise rib positions during normal respiration and assist in rib depression during forced expiration. What is the anatomical significance of the transversus thoracis muscle? The transversus thoracis muscle is located on the internal surface of the thoracic wall and acts as a weak depressor of the ribs during expiration. It arises from the inferior sternum and costal cartilage of the lower ribs, attaching to the internal surface of costal cartilages 2-6. Rate This Article