246 



Veins. 



596. The Vena azygos and Vena 

 hemiazygos. 



(Semi-diagrammatic.) 



The veins of the wall of 

 the thorax unite to form the 

 V. azygos. The right azy- 

 gos vein commences oppo- 

 site the I. or II. lumbar 

 vertebra from the Plexus 

 venosus lumbalis, .enters the 

 thorax through the aortic 

 opening in the diaphragm 

 and passes along the right 

 side of the vertebral column 

 to the III. dorsal vertebra, 

 where it arches forwards over 

 the root of the right lung and 

 terminates in the superior 

 V. cava. It receives 9 or 

 10 lower intercostal 

 veins, several o e s o p h a- 

 geal, mediastinal and 

 vertebral veins. 



The left, small azygos 

 vein or V. hzmiazyyos ascends 

 only as far as the VII. or 

 VIII. dorsal vertebra, and 

 then passes back to the 

 right azygos vein behind the 

 aorta. The upper left inter- 

 costal veins usually unite to 

 form tlieF. hemiazygos superior, 

 which opens into the! 7 , hemi- 

 azygos, but is also connected 

 with the left innominate vein. 

 The V. azygos and hemiazygos 

 vary a great deal as regards 

 their origin and course. 



