348 A MANUAL OF ANATOMY. 



position. Now this action substitutes a rift of greater for one 

 of less dimensions, and the result is to increase the dimen- 

 sions of the chest transversely, and anteroposteriorly by an 

 amount equal to the difference between the areas of the 

 sections of the thorax at the level of these two ribs. 



The Intercostal Veins. Fig. 74. 



These veins accompany the intercostal arteries and re- 

 turn the blood from the area which they supply. They 

 terminate by emptying into the veins described below. 



The Azygos Veins. Figs. 74, 73. 



These present numerous variations in formation, course, 

 and termination, but the following arrangement is the one 

 usually found. 



(1) The azygos major begins in the abdomen as a con- 

 tinuation of the ascending lumbar vein, or by a branch 

 from the right renal, or vena cava inferior. It enters the 

 chest through the aortic opening, lies to the right of the 

 aorta upon the intercostal arteries and vertebrae, and at the 

 level of the third or fourth dorsal vertebra arches over the 

 right bronchus and empties into the superior vena cava 

 (now removed) close to its pericardial attachment. It re- 

 ceives the nine or ten lower right intercostal veins, the 

 azygos minor (opposite the sixth or seventh dorsal verte- 

 bra), the right superior intercostal vein, the left azygos 

 superior (at times), the right mediastinal, bronchial, spinal, 

 and cesophageal veins. 



(2) The azygos minor also begins in the abdomen from 

 the left renal or ascending lumbar veins, enters the chest 

 through the left crus of the diaphragm, ascends at the left of 

 the vertebrae to the level of the seventh or eighth, then turns 

 to the right under the aorta to empty into the major azygos 

 at the level of the sixth or seventh vertebra. The minor 



