956 



A MANUAL OF ANATOMY 



mammary vein ; and (4) the first intercostal vein. The last-named 

 vessel, however, sometimes opens into the vertebral vein, and 

 occasionally the right inferior thyroid vein opens into the left 

 innominate vein. The left innominate vein receives, as an addi- 

 tional tributary, the left superior intercostal vein. 



Development. — The right innominate vein is developed from that portion 

 of the right anterior cardinal vein which intervenes between the place where 

 it receives the right subclavian vein and the place where the transverse j ugular 

 vein joins it. 



The left innominate vein is developed from the transverse jugular vein. 



Right Bronchus 



Right 



Pulmonary^ 



Artery 



Left Pulmonary Artery 



Left Bronchus 



Cu^^ , Left Pulmo- 

 r\-. i\\ .' jj^y Veins 



Fig. 392. — The Roots of the Lungs (Anterior View). 



Superior Vena Cava. — This vessel is formed by the union of the 

 right and left innominate veins behind the lower border of the 

 first right costal cartilage, close to the sternum. It is about 3 inches 

 in length, and descends almost vertically to the level of the upper 

 border of the third right costal cartilage, where it opens into the 

 postero-superior angle of tfie right auricle of the heart. In its course 

 it pierces the fibrous portion of the pericardium. The upper half 

 of the vessel is extrapericardial, and lies in the superior medias- 

 tinum ; but the lower half is intrapericardial, and lies in the middle 

 mediastinum. 



Relations — Upper Half — External. — The right phrenic nerve 

 and the right pleura. Internal. — ^The lower part of the innominate 

 artery. Lower Half — Internal. — ^The ascending aorta. Postcrior.- 

 The root of the right lung. The serous portion of the pericardium 



