THORACIC CAVITY in 



1. The intercostal vein of the first or highest space joins the right 



innominate vein (sometimes the vertebral vein). 



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



that of the fourth space) unite into a common trunk, termed the 

 right superior intercostal vein, which joins the upper part of the 

 vena azygos. 



3. The intercostal veins of the lower eight spaces join the vena azygos. 



On the left side of the body four modes of termination may 

 be recognised : 



1. The intercostal vein of the first space joins the left innominate vein 



(sometimes the vertebral vein). 



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 independently 

 of the first intercostal vein. 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). This has 

 already been studied, but -should now be revised (p. 29), 

 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 seventh 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. In addition to the intercostal veins it 

 receives the left bronchial veins. 



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

 This vein takes origin within the abdomen as the left 

 ascending lumbar 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 eighth or seventh 

 thoracic vertebra. At this point it turns to the right, and, 



