1st layer ◆Thymus ◆superior vena cava brachiocephalic veins Vagus ner Phrenic nerve Left Subclavian vein brachiocephalic Right vein brachiocephalic Vagus nerve vein crossing aortic arch Superior vena cava Phrenic nerves ◆Thymus ◆ superior vena cava ◆ brachiocephalic veins 1st layer