THE LYMPHATICS OF THE THORAX. 971 



which are associated more especially with the bronchi. The bronchial vessels take 

 their origin from a net-work contained in the walls of the bronchi, and are traceable 

 along the entire length of each bronchus and its branches until the terminal bronchi 

 are reached ; here the net-work disappears and no indications of it are to be found 

 in the walls of the atria or alveoli. In the larger bronchi the net-work is double^ 

 one portion of it occurring immediately beneath the mucous membrane and the 

 other external to the cartilaginous rings, but in the finer bronchi only one layer is 

 present and from this branches pass to the stems which accompany the arteries and 

 veins. All the stems belonging to this deep set of lymphatics pass to the hilus of 

 the lung and there open into the pulmonary nodes. 



The supei-ficial set consists of a net-work situated upon the surface of the lung, 

 immediately beneath the visceral layer of the pleura. The vessels composing it are well 

 supplied with valves and have communicating with them branches from the visceral 

 layer of the pleura and valved branches which have their origin in the interlobular and 

 intralobular connective tissue. No communication has been observed between the 

 superficial and deep pulmonary net-works, the stems from the superficial net-work 

 alone passing directly to the hilus of the lung to terminate in the pulmonary nodes. 



Lymphatic vessels have been demonstrated in the parietal layer of the pleura. 

 Those upon its costal surface communicate with the intercostal vessels ; those upon 

 the diaphragmatic surface with the diaphragmatic net-work ; and those upon the 

 mediastinal surface with the posterior mediastinal nodes. 



The CEsophagus. — The lymphatics of the oesophagus are arranged in two net- 

 works, one of which is submucous, while the other is situated in the muscular coat. 

 The stems which drain the net-works of the cervical portion of the oesophagus pass 

 to the superior deep cervical and the recurrential nodes, while those draining 

 the thoracic portions of the net-works pass to the posterior mediastinal nodes. 

 Finally, the stems originating in the net-works of the terminal portion pass to the 

 upper nodes of the coeliac group. 



Practical Considerations. — The Lymph- Nodes of the Thorax and Medias- 

 tinum. Anterior Mediastinum. — The nodes in close relation to the internal 

 mammary artery are of practical importance on account of their relations (a) to 

 the diaphragm ; (i^) to the anterior extremities of the intercostal spaces ; {c) to the 

 inner segment of the mammary gland. They may therefore be involved in cases 

 of subpleural (supradiaphragmatic) abscess, of tuberculous or syphilitic or typhoidal 

 caries of the ribs or sternum, or of carcinoma of the breast (page 2035). 



Middle Mediastinum. — The nodes just below the bifurcation of the trachea 

 (bronchial, peribronchial), in close relation to the trachea, the bronchi, and the 

 roots of the lungs, are frequently involved in tuberculous infection of the lungs. 

 The pulmonary lymphatics, both perivascular and peribronchial, communicate on 

 the one hand indirectly with the lymph-spaces in the walls of the alveoli beneath 

 the epithelial cells, and on the other with these nodes. Solid particles — and this 

 includes the bacillus tuberculosis and other organisms — are thus enabled tg pass from 

 within the alveoli into the lymphatic spaces, and from these they are forced on by 

 the respiratory movements of the lungs to the bronchial nodes, to which all the 

 lymphatics converge. These nodes often contain, especially in coal miners, or in the 

 inhabitants of large cities, a large amount of black pigment, consisting of minute 

 particles of dust, smoke (carbon), etc., that have been inhaled (Taylor). 



Caseation and ulceration of these nodes have involved the trachea (page 1840), 

 the bronchi (especially the right one, with which the larger number are in close 

 relation), and the oesophagus (page 16 14), directly in front of which some of them lie. 

 Their enlargement has also produced various pressure symptoms, — dyspnoea, dys- 

 phagia, stridulous respiration, etc., — which their relations -easily explain. 



Posterior Mediastimcm. — A group of nodes — oesophago-pericardiac (Leaf) — 

 lying between the posterior surface of the pericardium and the oesophagus, are in 

 close relation to the trunk of the pneumogastric nerve and its oesophageal branches. 

 Their infection — through their direct connection with the not infrequently infected 

 kiodes in the neck and thorax lying between the trachea and oesophagus — may produce 

 symptoms of vagus irritation. It has been thought (Guiteras) that these nodes and 



