PLEUEISY. 323 



connective tissue is continuous over the first rib with the con- 

 nective tissue which invests the pleural sac. The perforating 

 branches of the intercostal vessels and nerves also carry with 

 them sheaths of the same connective tissue which have been 

 prolonged along the main vessels and nerve trunks from the 

 posterior mediastinum. 



Owing to the laxity of the subjacent connective tissue, the 

 costal pleura is much more easily stripped from the parietes 

 than the visceral pleura is from the lung. 



The gangliated cord of the sympathetic lies over the heads of 

 the ribs in the connective tissue beneath the costal pleura, and 

 so the fibres which pass through the first and second dorsal 

 rami to ascend in the cervical chain to the eye may become 

 damaged when the pleura is inflamed. 



The pleural dome is occasionally infected by suppurative 

 processes in the lymphatic glands and connective tissue planes 

 of the neck. It is also liable to injury and infection from 

 wounds and operative procedures immediately above the clavicle. 

 Its relation to the subclavian artery is important in connexion 

 with aneurysms and ligature of that vessel. The continuity of 

 the axillary vascular and nervous sheaths with the connective 

 tissue over the pleural dome has already been mentioned. 



A close plexus of lymphatic vessels lies in the subpleural 

 tissue. The lymphatic efferents of the visceral pleura pass into 

 the superficial collecting trunks of the lung. Those of the costal 

 pleura open into the intercostal trunks; the diaphragmatic 

 pleura is drained by the diaphragmatic trunks and the medias- 

 tinal pleural lymphatics pass into the glands of the posterior 

 mediastinum. The pleural stomata, which are found in the 

 pleura covering the diaphragm and intercostal spaces, but not 

 in that of the mediastinum and ribs, facilitate the absorption of 

 fluid. The lymphatic trunks are provided with valves which 

 direct the flow away from the pleura. Thus the fluid which 

 normally transudes into the sacs from the blood-vessels is 

 constantly removed by the lymphatics through the agency of the 

 respiratory pump. In pleurisy the presence of inflammatory 



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