All of the following form boundaries of triangle of auscultation except?

Triangle of auscultation has the following boundaries: Superiorly and medially- Trapezius Inferiorly-Latissimus Dorsi Laterally-Scapula Floor -Serratus anterior, Erector spinae .Deep-Osseous poions of the 6th and 7th ribs ,internal ,external intercostal muscles. Typically, the Triangle of Auscultation is covered by the Scapula. To better expose the triangle and listen to respiratory sounds with a stethoscope, patients are asked to fold their arms across their chest, medially rotating the scapulae, while bending forward at the trunk, somewhat resembling a fetal position.