140 THORAX 



1. The highest intercostal vein, from the first space, joins the left in- 



nominate -vein (sometimes the vertebral vein), in the neck. 



2. The intercostal veins of the second and third spaces (and sometimes 



that of the fourth space) converge and by their union form a single 

 trunk, termed the left superior intercostal vein, which crosses the 

 arch of the aorta and joins the left innominate vein in the 

 thorax. The union with the left innominate vein may be 

 absent, and then the trunk formed by the veins of the second 

 and third spaces joins the accessory hemiazygos vein. 



3. The intercostal veins of the fourth, fifth, sixth, seventh, and eighth 



spaces terminate in the accessory hemiazygos vein (O.T. vena azygos 

 minor superior), which crosses posterior to the aorta and joins the 

 hemiazygos vein, or it ends directly in the vena azygos. 



4. The intercostal veins of the ninth, tenth, and eleventh spaces join the 



hemiazygos vein (O.T. vena azygos minor inferior). 



Vena Azygos (O.T. Vena Azygos Major). The azygos 

 vein has already been studied, but should now be revised 

 (p. 41), and then the dissector should examine the hemiazygos 

 and accessory hemiazygos veins. 



Vena Hemiazygos Accessoria. The accessory hemiazygos 

 vein is formed, on the left side of the body, by the union of the 

 intercostal veins of the fourth, fifth, sixth, seventh, and eighth 

 spaces. It communicates above with the left superior inter- 

 costal vein, which carries the blood from the second and third 

 intercostal spaces to the left innominate vein ; and it receives 

 the left bronchial veins. At the level of the eighth thoracic 

 vertebra it crosses to the right, posterior to the aorta and 

 thoracic duct, and ends by joining either the hemiazygos vein 

 or the vena azygos. It is very irregular both as regards its 

 tributaries and its termination. 



Vena Hemiazygos (O.T. Vena Azygos Minor Inferior). 

 The hemiazygos vein takes origin within the abdomen. It 

 is either the continuation upwards of the left ascending lumbar 

 vein or it springs from the left renal vein. It enters the 

 thorax by piercing the left crus of the diaphragm, and is 

 continued upwards, upon the vertebral column, as far as 

 the ninth or eighth thoracic vertebra. At that point it turns 

 to the right, and, crossing posterior to the aorta and the 

 thoracic duct, it joins the vena azygos. Before it terminates 

 it may receive the accessory hemiazygos vein. 



The thoracic tributaries of this vein are the intercostal 

 veins of the lower three spaces of the left side and the left 

 subcostal vein. In the abdomen it receives the upper two 

 left lumbar veins. 



The Anterior Intercostal Veins. The anterior inter- 



