Which of the following DOES NOT form boundary of triangle of auscultation?

The triangle of auscultation is a small triangular space on the back where the relatively thin musculature allows for respiratory sounds to be heard more clearly with a stethoscope. It has the following boundaries: Medial wall is formed by lateral border of trapezius Lateral wall is formed by medial border of scapula Inferiorly by the upper border of latissimus dorsi Floor is formed by: 7th rib, 6th and 7th intercostal spaces, rhomboids major On the left side, the cardiac orifice of the stomach lies deep to the triangle, and in days before X-rays were discovered the sounds of swallowed liquids were auscultated over this triangle.