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.
The breast is supplied with blood from above by the pectoral branch of the acromial thoracic artery, which leave's the axillary artery at the inner border of the pectoralis minor muscle. The pectoral branch descends between the pectoralis major and minor and anastomoses with the intercostals and long thoracic. It sends branches through the pectoralis major muscle, and in carcinoma of the gland it may be seen much enlarged running downward on the chest-wall beneath the muscle. From the inner side come the perforating branches of the internal mammary artery from the second to the sixth rib; the second, third, and fourth are the largest and may bleed freely in detaching the pectoralis major. To the outer side and below is the long thoracic artery, also called the external mammary; it descends along the outer edge of the pectoralis minor, sending branches inward around the edge of the pectoralis major to the mammary gland. The intercostal arteries also contribute somewhat to the blood supply of the gland.
Fig. 206. - Sagittal section of mamma of young woman who had never borne children; hardened in formalin. (Piersol).
The breast is exceedingly well supplied with lymphatics. They are composed of a deep set around the lobules and ducts, and a superficial set which together with the deep lymphatics forms a plexus around the nipple called the subareolar plexus. They drain mainly toward the axilla into the lymph-nodes along the edge of the pectoralis major but also communicate with the nodes around the subclavian artery and those in the anterior mediastinum which accompany the internal mammary artery.
The axillary nodes are in three sets: one along the edge of the pectoralis major muscle (pectoral nodes), another further back along the anterior edge of the scapula (scapular nodes), and a third following the course of the axillary artery
Fig. 207. - Lymphatics of the breast. (Poirier and Cuneo).
(humeral nodes). In addition to these there are some infraclavicular or subclavian nodes between the deltoid and pectoralis major and at the inner edge of the pectoralis minor muscles; these are comparatively rarely involved primarily. The axillary nodes are continuous and communicate with the subclavian and supraclavicular nodes, and these latter are frequently enlarged subsequent to the axillary infection. The anastomosis of the lymphatics across the median line has been thought to account for the occurrence of the disease in the opposite breast or axilla. As shown by Sappey, some if not all of the lymphatics of even the sternal portion of the breast drain into the axilla and not into the anterior mediastinum, thus accounting for the axillary involvement when the inner portion of the breast is affected. These five sets of nodes communicate with each other, and any one may be alone involved. The supraclavicular set do not become involved primarily because no vessels run directly from the breast to them; they are affected secondarily to involvement of the axillary or subclavian sets.
The deep lymphatics of the breast, according to Sappey, follow the ducts to the areola, there anastomosing with the superficial lymphatics to form what he called the subareolar plexus, which drains by two trunks into the axilla. The lymphatics of the breast anastomose with those of the surrounding structures; hence in certain cases the pectoralis muscles and even the pleura may be affected, and when the disease is widely disseminated by the lymph-channels on the chest-walls there is produced the thickened, brawny, infiltrated condition known as the cancer "en cuirasse" of Velpeau. Nerves. - The breast and the skin over it are supplied from the descending branches of the cervical plexus, by thoracic branches from the brachial plexus, and by the second, third, fourth, fifth, and sixth intercostals. These are not of so much practical importance as the lateral branches of the second and third intercostal nerves. That of the second is called the intercostobrachialis (humeral) nerve; it crosses the axilla, anastomoses with the medial brachial (lesser internal) cutaneous nerve, and supplies the skin of the inner and upper portion of the arm. The third intercostal anastomoses with the second and gives a branch to the arm and to the dorsum of the scapula. These nerves are certain to be seen in clearing out the axilla. Their division is accompanied by no paralysis, but disturbance of them accounts for some of the pain and discomfort following the operation.