Lymph Vessels of the Mammary Glands (Appended Section)

The lymph vessels of the mammary glands (Figure 30) drain to the superficial inguinal, axillary, and sternal lymph nodes.^[1] The lymph vessels from the caudal half of the mammary chain, including the 3 caudal of the 5 teats, drain to the superficial inguinal lymph nodes (Figure 30: 1, 1¹). The lymph vessels from the cranial half of the mammary chain, including the 3 cranial of the 5 teats, drain to the axillary lymph node. If an accessory axillary lymph node (Figure 30: 2) is present, some vessels will also drain to it, with the remainder draining to the sternal lymph node. The lymph vessels from the middle part of the mammary chain, corresponding to the 3^rd teat, drain to all lymph node groups.

The lymph vessels of the teats and the skin of the mammary glands form subcutaneous, coarsely meshed networks (Figure 30), from which the lymph vessels that lead to the aforementioned lymph nodes emerge. Most of these lymph vessels run subcutaneously to the lateral edge of the mammary chain and, as shown in Figure 30, then run either cranial to drain to the axillary lymph node (Figure 30: 2), or caudal to the superficial inguinal lymph nodes (Figure 30: 1, 1’). However, some of the lymph vessels (Figure 30: c, c) also enter the mammary gland parenchyma, passing through it to run between the mammary glands and the ventral abdominal and thoracic walls to drain to the aforementioned lymph nodes, most gradually curving towards the lateral edge of the mammary chain and joining the lymph vessels described above. Additionally, some of the lymph vessels passing through the mammary parenchyma drain to the sternal lymph node, joining with the corresponding lymph vessels of the mammary parenchyma (see below). This behaviour was demonstrated only by the lymph vessels originating from the cranial 2 or 3 teats, or their skin, though not by the lymph vessels from the skin between these teats.

All these lymph vessels, including the lymph vessels that form the networks, are remarkable because of their considerable strength (thickness).

Some of the lymph vessels of the mammary parenchyma emerge subcutaneously in various places along the surface of the mammary parenchyma (Figure 30: a, a), joining with the lymph vessels or networks of the skin. Other lymph vessels merge with the cutaneous lymph vessels that penetrate the mammary parenchyma, running between the mammary glands and the ventral abdominal and thoracic walls to drain to the aforementioned lymph nodes (superficial inguinal and axillary lymph nodes) (Figure 30: b, b), most also curving toward the lateral margin of the mammary chain (see above). However, some of the lymph vessels running deep to the mammary parenchyma also drain to the sternal lymph node; 1 to 2 lymph vessels (Figure 30: e) from the middle part of the mammary chain, corresponding approximately to the 3^rd teat, travel deeply between the xiphoid cartilage and the last true costal cartilage, accompanied by the cranial epigastric artery and vein, before running under the diaphragmatic attachment into the thoracic cavity and then to the sternal lymph node. Furthermore, several lymph vessels (Figure 30: e’, e’’) from the cranial part of the mammary chain, corresponding to the 1^st and 2^nd teats, enter the thoracic cavity through the M. pectoralis profundus and then through the intercartilaginous spaces (usually 1 lymph vessel passing through each of the 4^th, 5^th, and 6^th intercartilaginous spaces), joining the aforementioned lymph vessels and draining with them to the sternal lymph node.

It should be emphasized that I have injected such lymph vessels not only from the mammary parenchyma, but also from the 1^st, 2^nd, and 3^rd teats, although the injection was certainly not successful every time.

The lymph vessels of the mammary parenchyma have not been observed crossing the median plane to the contralateral side, although this region has frequently been injected and examined. However, lymph vessels of the skin of the mammary glands adjacent to the median line may cross to the other side.