ANATOMY IN A NUTSHELL. 483 



passes downward to join the left innominate vein at the inferior border of the 

 first right costal cartilage to make the superior vena cava. Its radicles are. 

 (a) right vertebral, (b) right internal mammary, which are two for each artery 

 but uniting into a common trunk before entering into the innominate vein, 

 (c) right inferior thyroid, which are three or four in number pass from the thy- 

 roid venous plexus into the left innominate vein, (d) right superior intercostal, 

 receives the blood from the second and third intercostal spaces. 

 The right lymphatic duct opens at the angle where the right subclavian vein 

 joins the right internal jugular vein. 



The left innominate vein, which is about three inches long, is larger than 

 the right. It is formed by the left internal jugular vein and the left subclavian 

 vein at the inner end of the clavicle. It joins the right innominate vein to 

 form the superior vena cava. The innominate veins have no valves. The 

 radicles of the left innominate vein are, (a) left vertebral, (b) left internal 

 mammary, which are two for each artery but unite into a common trunk 

 before entering into the innominate vein, (c) left inferior thyroid, which are 

 three or four in number pass from the thyroid venous plexus into the left innom- 

 inate vein, (d) the left superior intercostal receives the blood from the second 

 and third intercostal spaces. 



The one on the right side passes down to enter the vena azygos major, 

 while the one on the left side passes across the arch of the aorta to enter the 

 left innominate vein, and receives the left bronchial vein. The highest inter- 

 costal vein, which comes from the first intercostal space, empties into the cor- 

 responding vertebral or innominate vein. 



The superior vena cava is formed by the two innominate veins behind the 

 junction of the first right costal cartilage with the sternum. It is about three 

 inches long and passes clown into the right auricle opposite the upper border 

 of the third right costal cartilage. This vein has no valves. Its radicles are, 

 (a) pericardiac, (b) mediastinal, (c) vena azygos major. It collects the blood 

 from the upper half. of the body. 



When the blood is given off from the thoracic aorta into the intercostal 

 arteries, it comes back by the intercostal veins, which would have no place to 

 empty unless there was a special provision made for them. They cannot empty 

 into the heart, and the inferior vena cava has no length above the Diaphragm, 

 and the superior vena cava is too high for most of them, so they empty into 

 veins called azygos veins which connect the superior and inferior vena cava. 

 The azygos veins have no valves, but their tributaries do have valves. The 

 azygos veins are: (Plate CXCV). 



1. The vena azygos major, also called right azygos vein. This vein com- 

 mences at the first or second lumbar vertebra by a branch from (a) right lum- 

 bar veins, (b) or by a branch from the righl renal vein, (c) or by a branch from 

 the inferior vena cava. After passing through the aortic opening in the Dia- 

 phragm, it passes to the fourth dorsal vertebra along the right side of the ver- 

 tebral column and ends in the superior ven cava just before it enters the per- 

 icardium. Its radicle.- are. (a) the lower ten intercostal veins on the righl side, 



