Identify the origin, insertion, and actions of teres major.

• A. Origin: superior angle of the scapula. Insertion: medial lip of intertubercular groove of the humerus. Action: adducts and medially rotates the humerus; assists in extension.
• B. Origin: lateral border of the scapula. Insertion: intertubercular groove; Action: adduction.
• C. Origin: inferior angle of the scapula. Insertion: medial lip of intertubercular groove of the humerus. Action: adducts and medially rotates the humerus; assists in extension.
• D. Origin: subscapular fossa. Insertion: greater tubercle. Action: external rotation.

Answer: (C)

Teres major originates from the inferior angle of the scapula and inserts on the medial lip of the intertubercular groove of the humerus. Its actions are to adduct the arm and medially rotate it, and it also assists in extending the shoulder, especially when the arm is flexed. This combination of origin, insertion, and action explains why it pulls the humerus toward the body, rotates it inward, and can help move the arm from a flexed position toward extension. The other descriptions mix up the attachments or the function (for example, wrong origin points or insertion sites that belong to other muscles), so they don’t align with teres major’s actual anatomy.