Chapter 6 The Muscular System 187 Copyright Goodheart-Willcox Co., Inc. Erector spinae muscle group External intercostal External oblique Internal intercostal Internal oblique External oblique (cut and pulled back) Rectus abdominis C7 Erector spinae: Illiocostalis Longissimus Spinalis Quadratus lumborum T1 Abdominal aponeurosis Trapezius Anterior view Posterior view of superficial muscles Posterior view of deep muscles © Body Scientific International Figure 6.17 Major muscles of the trunk.