The thoracic intercostal space located deep to the triangle of auscultation is which numbered space?

• A. Fifth
• B. Sixth
• C. Seventh
• D. Eighth

Answer: (B)

The triangle of auscultation is a small, relatively thin area on the back that makes lung listening easier because fewer muscles cover it. It’s bounded by the trapezius on the top, the latissimus dorsi below, and the medial border of the scapula laterally, with the floor formed by intercostal muscles (and some underlying rhomboid major). This spot lies over the intercostal space at about the level of the inferior angle of the scapula, in the mid-scapular region. Thus the intercostal space deep to this triangle is the one at that level—roughly the intercostal space around the inferior scapular border. This is why placing a stethoscope there allows better auscultation of the lungs.