AZYGOS VEINS. 483 



spinal branch to the vertebra and the spinal cord. See VESSELS 



OF THE SPINAL CANAL (p. 549). 



The intercostal vein closely resembles the artery in its course and intercostal 

 branching. Xear the head of the rib it receives a contributing vein ' 

 dorsal branch, and then joins an azygos vein. 



Bronchial veins. A vein issues from the root of each lung, and Vein of the 

 ends on the right side in the large azygos vein, and on the left in lung ' 

 the superior azygos vein of its own side. 



The SUPERIOR INTERCOSTAL ARTERY of the Sllbclavian trunk Superior 



descends over the neck of the first rib, external to the cord of m 

 the sympathetic, and supplies a branch to the first intercostal supplies two 

 space : continuing to the second space, which it supplies in like s P aces 

 manner, it ends by anastomosing with the upper aortic intercostal. 



Its intercostal offsets divide into anterior and posterior branches, 

 which are distributed like the intercostal branches of the aorta. 



The AZYGOS VEINS are two in number on the left side and one on Three azygos 

 the right, and receive branches corresponding to the offsets furnished ^ eins - 

 by the descending thoracic aorta. 



The right or large azygos (fig. 174, p. 481, and fig. 175, 3 , p. 486) Large 

 begins in the right ascending lumbar vein on the right side of the ri^iftside, n 

 spine in the abdomen. It enters the thorax through the aortic 

 opening of the diaphragm, and ascends on the right side of the 

 aorta and thoracic duct, over the intercostal arteries and the bodies 

 of the vertebra. Opposite the fifth rib the vein arches forwards 

 above the root of the right lung, and enters the superior cava as and joins 

 this vessel pierces the pericardium. Its valves are few and very 

 incomplete, and the intraspinal and intercostal veins may be 

 injected through it. 



Branches. In this vein are received : branches 



1. Eight lower intercostal veins of the right side. 



2. Right superior intercostal vein bringing blood from the second 

 and third spaces. 



3. Left lower azygos vein, bringing blood from the lower three 

 or four spaces of the left side. 



4. Left upper azygos vein bringing blood from the fourth, fifth, 

 sixth, and seventh spaces of the left side. 



5. Right bronchial vein. 



6. Small cesophageal, mediastinal, and vertebral veins. 



By means of the right azygos vein the inferior vena cava 

 communicates with the superior, so that blood can reach the heart 

 from the lower half of the body if the inferior cava were obstructed. 



The left lower azygos vein (fig. 175, 4 ) begins in the abdomen in Left lower 

 the ascending lumbar vein of the left side of the vertebral column. az yg s 

 Entering the thorax along the aorta, or through the crus of the begins in 

 diaphragm, the vein ascends on the left of the aorta as high as the abdom en, 

 ninth or eighth dorsal vertebra, where it crosses beneath that vessel ends in 

 and the thoracic duct to end in the right azygos. It receives the azygos : 

 three or four lower intercostal veins of the left side, and some branches, 

 cesophageal and mediastinal branches. 



The left upper azygos vein (fig. 175, 5 ) is formed by offsets from Left upper 



1 I 2 Vein - 



