A 48-year-old female patient presents to your office with a complaint of swelling in her left arm for the past two weeks. She has a history of breast cancer and underwent a left mastectomy and axillary lymph node dissection six months ago. On physical examination, you notice non-pitting edema in her left upper extremity. Which of the following structures is most likely affected by the patient’s lymphatic drainage disruption in the left upper extremity?