A 26-year-old male presents to clinic with complaints of worsening asthma. He has a long history of asthma and has now begun to use his rescue inhaler more frequently. He also states that he wakes up at night due to his asthma. Physical examination reveals mild wheezes bilaterally. In addition to starting the patient on a low-dose inhaled glucocorticoid, osteopathic manipulative treatments are initiated. Osteopathic structural examination reveals restriction of motion in ribs 4-6 on the left during inhalation. Which of the following muscles should initial treatment be focused towards?