![]() ![]() Since the left and right mediastinal lymph nodes behave differently as a result of the different anatomical topography between the sides, the lymph nodes on the left and right sides should be considered separately, even though a sharp distinction between the two groups is not possible in many cases. In young animals, they are partly enclosed by the thymus. The mediastinal lymph nodes are embedded in fat and lie in an unorganized manner towards the midline of the body, between the pleurae of the mediastinum in the precardiac mediastinal space. The tracheobronchial ( bifurcationis) lymph node ( Figure 17: b, b’ 18: 1, 2) can be easily mistaken for a caudal mediastinal lymph node and has been previously identified as such (by Ellenberger-Baum, Chaveau-Arloing and Bucher ). A caudal mediastinal lymph node was not found in any of the numerous cases examined. This lymph node will be described in more detail below, and to facilitate the description of its afferent drainage, it will be referred to as the main (cranial) mediastinal lymph node. One of the mediastinal lymph nodes is notably constant in its occurrence and position and lies in the 1 st intercostal space, just cranial to the costocervical vein. For these reasons, the middle and cranial mediastinal lymph nodes are described together in the following sections, and the term mediastinal lymph nodes is used, but these descriptions are almost exclusively of the behaviour of the cranial mediastinal lymph nodes. The middle mediastinal lymph node only rarely occurs, is usually poorly distinguishable from the cranial mediastinal lymph nodes, and shares the same afferent drainage. The cranial mediastinal lymph nodes are sometimes joined by a lymph node, which is, strictly speaking, a middle mediastinal lymph node, as it lies in the cardiac mediastinum. This lymph node is sometimes found on the left side of the pericardium, where the aortic arch emerges, near the cranial border of the pericardium ( Figure 17: a 2), and sometimes on the right or dorsal side of the trachea, just cranial to the azygos vein ( Figure 18: 3 2), at times partly or entirely between the trachea and azygos vein. lymph nodes that lie between the 1 st rib and the heart in the precardiac mediastinum. While in cattle there are cranial, middle, caudal, dorsal, and ventral mediastinal lymph nodes (see Baum page 29), in dogs there are only the cranial mediastinal lymph nodes, i.e. lymph nodes located in the mediastinum, occur infrequently in dogs, in much fewer numbers and in much fewer groups than in cattle. ![]()
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