470 



VEINS OF THE TRUXK. 



that opening through the fibres of the diaphragm, the azygos vein ascends 



Fig. 320. Fig. 320. SKETCH OP THE PRINCIPAL SYSTEMIC 



VENOUS TRUNKS, THE AZYGOS, AND INTERCOSTAL 

 VEINS. 



For the detailed description of this figure see 

 p. 454. The following indications relate to the 

 accompanying part of the text : 8, the right, 8', 

 the left, superior intercostal veins ; 9, the main 

 trunk of the azygos vein; the uppermost number 

 ri marks its junction with the superior cava, the 



\'~5 a . lowest its passage into the abdomen ; 9', the left or 



hemiazgyos ; 10, thoracic duct; 11, inferior vena 

 cava ; 12, the union of a branch of the left azygos 

 with the left renal vein; 13, 13', the right and 

 left azygos veins continued down into the abdomen, 

 and joining some of the lumbar veins; 15, union 

 of lumbar, ilio-luinbar, and sacral veins. 



on the bodies of the dorsal vertebrse, until 

 it arrives opposite the root of the right 

 lung, over which it arches forwards, and 

 then opens into the upper vena cava, im- 

 mediately above the point at which that 

 vessel is invested by the pericardium. 

 When passing through the opening in the 

 diaphragm, this vein is accompanied by the 

 thoracic duct, both being situated on the 

 right side of- the aorta. In the thorax, 

 maintaining the same position with respect 

 to the duct and the oesophagus, it passes in 

 front of the intercostal arteries 1 , and is 

 covered by the pleura. It is joined by 

 the several veins which accompany the 

 aortic intercostal arteries of the right side ; 

 and, at about the sixth or seventh dorsal 

 vertebra, by the left or smaller azygos 

 vein. It is also joined by several oesopha- 

 geal and other small veins, and near its 

 termination by the bronchial vein of the 

 right lung ; and it is generally connected 

 with the right superior intercostal vein. 

 As it communicates below with the vena 

 cava inferior through one of the branches 

 of that large vein, while it terminates above 

 in the vena cava superior, it forms a con- 

 nection between those two vessels. A few 

 valves of imperfect formation have been 

 found in the azygos vein ; its branches 

 (intercostal veins) are provided with distinct 

 valves. 



On the left side of the chest the veins 

 of the three or four upper intercostal 

 spaces are usually united into one trunk, 

 forming the left superior intercostal vein, which (as already mentioned at 



