DISEASES OF THE MEDIASTINUM. 



Anatomical Conditions. The mediastinum is the central space 

 in the chest, Umited on each side (right and left) by the two 

 layers of parietal pleurae, which close the cavities (pleural) oc- 

 cupied by the right and left lung respectively. 



It contains the heart and pericardium, occupying, in the 

 horse, the space between the third and seventh ribs, and above 

 this the roots of the large vessels (aorta, anterior and posterior 

 aortas, pulmonary artery and its first divisions, the anterior and 

 posterior venae cavas), the vena asygos, the thoracic duct, the 

 trachea with its bifurcation, the tracheal and bronchial lymph 

 glands, the oesophagus, and the vagus, phrenic, sympathetic and 

 left recurrent laryngeal nerves. In front of the heart it con- 

 tains the two innominate arteries and their divisions, the conflu- 

 ence of the jugular veins, and anterior vena cava, and their af- 

 fluents, the trachea and oesophagus and their lymph glands, the 

 remnant of the thymus, and the vagus, sympathetic, phrenic 

 and left recurrent laryngeal nerves. Behind the heart the struc- 

 tures occupying the mediastinum are the oesophagus and oeso- 

 phagean lymph glands, the abdominal branches of the vagus, 

 sympathetic and phrenic nerves, and at its upper border the pos- 

 terior aorta, vena asygos, thoracic duct, sympathetic nerve 

 trunks and ganglia and the dorsal lymph glands. Smaller 

 lymph glands and nodes are scattered throughout the medias- 

 tinum, and into the lymph glands drain the lymph currents from 

 the structures adjacent to each (lung, bronchia, trachea, oesoph- 

 agus, heart, pericardium, pleurae, thymus, supporting con- 

 nective tissue, nerves, vessels, etc. ) Thus any advancing or in- 

 fective disease in any of these organs is liable to produce sec- 

 ondary affections in the mediastinal lymph glands. Their in- 

 timate connection with the diaphragm and through that and the 

 thoracic duct with the abdominal organs, lays these glands open 

 to infection and disease which has commenced outside the thoracic 

 cavity proper. 



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