Through which muscle must you palpate to isolate the intercostalis?

• A. Pectoralis major, latissimus dorsi, external oblique
• B. Pectoralis major
• C. Latissimus dorsi
• D. External oblique

Answer: (D)

The intercostalis lie between the ribs, so to feel them you access the deeper thoracic layer by palpating through a superficial muscle that overlays that region. The external oblique sits right over the lateral thorax and upper abdomen, directly covering the intercostal spaces. By pressing through the external oblique, you can reach and feel the intercostal fibers as they run between the ribs, especially with breathing which makes them contract. The other muscles—pectoralis major and latissimus dorsi—are positioned differently on the chest and back and don’t provide the correct access route to isolate the intercostal muscles.