This section is from the book "Applied Anatomy: The Construction Of The Human Body", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body.
There are two sets of lymphatic nodes in the axillary region, the axillary nodes proper and the subclavian nodes.
The number of the nodes varies from about ten or twelve to twenty or more. When enlarged they are readily seen, but after the surgeon has carefully dissected away all the nodes he can possibly find disease may subsequently reveal the existence of others. Hence it is impossible ever to be absolutely sure that all nodes have been removed.
The subclavian nodes, about two or three in number, lie in the infraclavicular triangle between the pectoralis major and deltoid muscles and on the front of the subclavian vein above the pectoralis minor muscle. They receive radicles from the mammary gland as well as from the axillary groups.
The humeral set, perhaps eight or nine, accompany the axillary artery and vein and lie along them and in the axillary fat. They receive mainly the lymphatics from the arm. They can often be pared off the vessels with ease, but sometimes are so firmly attached that the vessels are injured in their removal.
Fig. 275. - Lymphatics of mammary gland, and axillary nodes. (Poirier and Cuneo).
The anterior or thoracic set accompany the long thoracic artery along the lower border of the pectoral muscles. They are not so numerous as the humeral set, perhaps four or five in number, and drain the anterior upper half of the chest above the umbilicus, including the mammary gland (Fig. 275).
The posterior or scapular set accompany the subscapular artery along the posterior portion of the axilla. They are about as numerous as the anterior set and drain the upper posterior portion of the chest, the scapula and lower portion of the neck.
The lymphatics of the middle and lower portion of the back as low down as the umbilicus (3 to 4 cm. above the iliac crest) also drain into the axilla.
These lymphatic nodes communicate with one another, so that it does not of necessity follow that if the part ordinarily drained by a certain set is affected the nearest nodes will be involved. It usually is so, but not always. The infection may pass by or through one set of nodes and involve a neighboring communicating set. It happens in carcinoma of the breast that sometimes the posterior or scapular set are involved and the anterior or thoracic set escape. This has already been alluded to in the section on the mammary gland (see page 184). These three sets drain into the subclavian nodes and then empty into the subclavian vein near its junction with the jugular.