Lymph Vessels of the Diaphragm

The lymph vessels of the diaphragm (Figures 17; 18; 27) drain to the middle tracheobronchial, sternal, cranial lumbar aortic, left hepatic, splenic and gastric lymph nodes and showed the following behaviour:

a. Lymph Vessels of the Pars Costalis and Pars Sternalis

Most lymph vessels of the pars costalis and pars sternalis drain to the sternal lymph node, as well as to a lesser extent to lymph nodes located at the stomach (left hepatic, splenic, and gastric lymph nodes), to the middle tracheobronchial lymph node, and to the cranial lumbar aortic lymph nodes. When the muscle layer of the pars costalis and pars sternalis of the diaphragm is injected by puncture (Figures 17: 7; 18: w), the lymph vessels that fill initially form very coarsely meshed networks under the pleura of these parts of the diaphragm, as shown in Figures 17 and 18.

The lymph vessels arising from these networks travel in 3 different patterns:

Pattern 1

The lymph vessels arise on each side, underneath the pleura, to the point of attachment of the pars costalis on the ribs, and merge to form 1 to 2 larger lymph vessels, or trunks, which run ventrally under the pleura at the attachment of the pars costalis to the sternum. From there, they then travel under the M. transversus thoracis, and, now on the inner surface of the sternum, covered by the M. transversus thoracis and accompanied by the A. and V. mammaria interna, run on each side of the neck up to the sternal lymph node (Figures 17: c; 18: 6). Because the 1 to 2 lymph trunks often divide and reunite with their sub-branches, networks with very coarse meshes are created, and in many locations, it appears that 3 to 4 lymph vessels lie next to each other. The subpleural networks also fill up with dye when either the peritoneum of the diaphragm or the subperitoneal portion of the muscles are injected by puncture. It is also interesting to note that lymph vessels can drain to both sternal lymph nodes when only one-half of the diaphragm is injected. For example, in one case, the lymph vessels ran from the left pars costalis of the diaphragm together with the left mammary artery and vein to the 4^th inter-cartilage space. From there, only some of the vessels traveled to the left sternal lymph node, while the remainder passed over the median plane and drained into the right sternal lymph node.

Pattern 2

From the aforementioned subpleural network, several subpleural lymph vessels continue on each side near the diaphragmatic pillars. One to 2 of these lymph vessels run towards the heart in the postcardial mediastinum, usually near the truncus esophagus ventralis of the vagus nerves, and drain to the middle tracheobronchial lymph node as shown in Figures 17 and 18, while 2 to 3 of these lymph vessels (Figures 17: e, f; 18: 7) enter the abdominal cavity, either with the esophagus or directly through the diaphragmatic muscle near the diaphragmatic tendon, and subsequently to lymph nodes that are located in the abdominal cavity by the stomach, specifically the left hepatic lymph node (Figure 28: 1), the splenic lymph nodes (Figure 28: 8), and the gastric lymph node. These lymph vessels demonstrate the same behaviour as those of the end of the esophagus (see lymph vessels of the esophagus), however, individual lymph vessels may also ascend subperitoneally on the diaphragm (Figure 27: 13) and drain into the cranial lumbar aortic lymph node. For the sake of completeness, it should be emphasized that no lymph vessels drained to the right hepatic lymph nodes, not even those from the right pars costalis of the diaphragm. Of course, these lymph vessels and networks do not all fill with each injection.

Pattern 3

Finally, some of the lymph vessels of the pars costalis of the diaphragm drain to the cranial lumbar aortic lymph node. These lymph vessels originate from the dorsal aspect of the pars costalis, and in contrast to the aforementioned lymph vessels, only some of them run subpleural (Figures 17: d’; 18: 8), and others run subperitoneal (Figure 27: 12, 13). Both groups curve towards the aortic hiatus. The subpleural lymph vessels either enter the abdominal cavity through the aortic hiatus, or penetrate the muscles close to the aortic hiatus and join the subperitoneal lymph vessels. Finally, all the lymph vessels merge to form 2 to 3 vessels on each side, which drain to the cranial lumbar aortic lymph node.

b. Lymph Vessels of the Pars Lumbalis

Most of the lymph vessels of the pars lumbalis of the diaphragm (Figures 17: 7²; 18: w¹; 27: a²) are part of the group described in Pattern 3 above (Figures 17: d; 18: 8; 27: 13) for the pars costalis, while a smaller number are part of the group described in Pattern 2 above, and drain together with the lymph vessels in these groups to the middle tracheobronchial lymph node, the cranial lumbar aortic lymph node, the splenic lymph nodes, and the gastric lymph node. Some of the lymph vessels leading to the three latter groups of lymph nodes can, however, also extend subperitoneally.

c. Lymph Vessels of the Diaphragmatic Tendon

The lymph vessels of the diaphragmatic tendon (Figures 17: 7¹; 18: w²) form extremely rich and fine networks, again subpleural. The lymph vessels arising from these networks merge with the lymph vessels of the muscular part (pars costalis and pars lumbalis) of the diaphragm and consequently also drain to the same lymph nodes as them.

When the pleura covering the diaphragm is punctured and injected, the same subpleural networks and the lymph vessels developing from them fill as described above under A, B, and C. When the peritoneum covering the diaphragm is punctured and injected, subperitoneal lymph networks fill up on the diaphragmatic muscle, but they do not stand out as clearly as the subpleural networks, which fill at the same time from the subperitoneal networks. There are evidently still intermuscular networks between the subperitoneal and subpleural networks, as described in the cow, although they cannot be recognized macroscopically with absolute certainty in the dog, given the small size of this species. Macroscopic subperitoneal networks could not be detected on the diaphragmatic tendon with certainty even when the peritoneum was punctured, in contrast to the cow (see Baum [6] page 115). The above findings demonstrate that lymph flow must occur from the abdominal cavity to the thoracic cavity side of the diaphragm, which has been previously demonstrated in the cow. Lymph vessels of the peritoneum are connected to the diaphragmatic lymph vessels (see lymph vessels of the peritoneum).

The lymph vessels of the diaphragm were almost all filled by puncture injection because this method is very easy and convenient, however, filling can also be achieved by introducing the coloured injection fluid into either the pleural or peritoneal cavity, or into both, and performing artificial respiration. Respiratory movements were usually performed for several hours. Nonetheless, the filling of the lymph vessels was not nearly as complete as that obtained by injection.