Which muscle inserts at the floor of the intertubercular sulcus of the humerus?

• A. Pectoralis Major
• B. Deltoid
• C. Latissimus Dorsi
• D. Teres Major

Answer: (C)

The intertubercular sulcus has distinct zones where different muscles attach, and the floor of that groove is where the long, strong tendon of the latissimus dorsi anchors. This placement lets latissimus dorsi extend, adduct, and medially rotate the arm effectively as it pulls the humerus toward the body. In contrast, the pectoralis major attaches to the lateral lip of the groove, teres major to the medial lip, and the deltoid attaches to the deltoid tuberosity away from the groove, so they don’t insert at the floor. Thus, the muscle that inserts at the floor of the intertubercular sulcus is the latissimus dorsi.