THE LYMPHATIC STRUCTURES OF THE THORAX

There are very numerous lymph nodes within the thorax. Although most are collected in groups, these are some­times less discrete than is often suggested, and the prov­enance of the more scattered nodes may be difficult to determine.

Small intercostal nodes lie in the dorsal part of some intercostal spaces. They receive lymph from the verte­brae and the adjacent muscles, the dorsal part of the diaphragm, and the local costal and mediastinal pleura. The efferent flow is to the thoracic duct.

The cranial mediastinal nodes are numerous and scat­tered about the esophagus, trachea, and vessels at the entrance to the thorax; usually some form a discontinu­ous chain that joins the caudal deep cervical nodes within the neck. The most caudal members reach the pericardium, where they overlap the nodes about the tracheal bifurcation that are assigned to the tracheo­bronchial and caudal mediastinal groups. Most efferent vessels pass to the thoracic duct; those from the most cranial nodes in the series may first perfuse deep cervical nodes.

The tracheobronchial group is scattered about the caudal part of the trachea and the chief bronchi (Figure 20-5/5); left, middle, and right subdivisions are com­monly distinguished. Small nodes within the peribron­chial tissue of the lung may be regarded as members of this series. Most lymph passing through this group has origins within the lungs, but some comes from the peri­cardium, the heart, and the caudal mediastinal nodes. The efferent vessels are divided between those that go directly to the thoracic duct and those that first perfuse the cranial mediastinal nodes.

A number of small caudal mediastinal nodes lie directly in front of the diaphragm and between the esophagus and aorta. Lymph is received from the esophagus, the diaphragm, the liver, the mediastinal and diaphragmatic pleura, and, apparently, the lungs. The efferent lymph flow is divided between the thoracic duct and the tracheobronchial and cranial mediastinal lymph nodes.

The few ventral mediastinal lymph nodes are without significance.

The thoracic duct exhibits no important distinctive features. It drains into one or another of the large veins at the entrance to the thorax, most commonly the cranial vena cava.