Lymph nodes draining the breast and lying behind the pectoralis minor are labelled as:

Axillary nodes receive more than 75% of the lymph from the breast. There are 20-40 nodes, grouped aificially as pectoral (anterior), subscapular (posterior), central and apical. Surgically, the nodes are described in relation to pectoralis minor. Those lying below pectoralis minor are the low nodes (level 1), those behind the muscle are the middle group (level 2), while the nodes between the upper border of pectoralis minor and the lower border of the clavicle are the upper or apical nodes (level 3). Ref: Gray's anatomy 40th edition, Chapter 58.