THE INNOMINATE VEINS 641 



I. THE VEINS OF THE HEART 



The veins of the heart have already been described (p. 520). 



n. THE VENA CAVA SUPERIOR AND ITS TRIBUTARIES 



THE VENA CAVA SUPERIOR 



The vena cava superior (fig. 509) carries to the heart the blood returned from 

 the head and neck and upper extremities through the right and left innominate 

 veins, and from the walls of the thorax, either directly through the azygos vein, 

 or indirectly through the innominate veins. It is formed (fig. 509) by the con- 

 fluence of the right and left innominate veins behind the first right sterno-chondral 

 articulation. Descending from its origin in a gentle curve with its convexity to 

 the right and in a chrection slightly backward behind the sternal end of the first 

 and second intercostal spaces and second costal cartilage, it terminates in the 

 right atrium of the heart on a level with the third right costal cartilage in front and 

 the seventh thoracic vertebra behind. It measures about 7 to 8 cm. (3 in.) in 

 length. A little more than its lower half (4 cm.) is contained within the pericar- 

 dium, the serous laj^er of that membrane being reflected obliquely over it imme- 

 diately below the spot where it is joined by the vena azygos, and on a lower 

 level than the reflexion of the pericardium on the aorta. The superior vena 

 cava contains no valves. 



Relations. — In front, in addition to the first and second intercostal spaces and the second 

 costal cartilage, it is covered by the remains of the thymus gland, the intrathoracic fascia, and 

 the pericardium, and is overlapped by the right pleura and lung. 



Behind (fig. 509 j are the vena azygos (major), the right bronchus, the right pulmonary 

 artery, and the superior right pulmonary vein; and below, the fibrous layer of the pericardium. 

 The serous layer is reflected over the front and sides of the vessel, but not over its posterior 

 part. 



To the right side are the right lung and pleura and the phrenic nerve. 



To the left side are the innominate artery and the ascending aorta. 



Tributaries. — In addition to the right and left innominate veins and the vena 

 azygos it receives small veins from the mediastinum and pericardium. 



THE INNOMINATE VEINS 



The innominate or brachio-cephalic veins [vv. anonymse] return the blood 

 from the head and neck and upper extremity. They are formed on each side by 

 the confluence of the internal jugular and subclavian veins behind the sternal 

 end of the clavicle. They terminate behind the first costal cartilage on the right 

 side by uniting to form the vena cava superior. The innominate veins have no 

 valves. 



The right innominate vein [v. anonyma dextra] (fig. 509) measures about 2 to 

 3 cm. (1 to Ij in.) in length, and descends from its origin behind the sternal end 

 of the clavicle, very slightly forward and medially, along the right side of the sub- 

 clavian and innominate arteries, to its junction with the left vein behind the first 

 costal cartilage close to the sternum. It is superficial to the innominate artery. 



Relations. — In front are the origins of the sterno-hyoid and sterno-thjTeoid muscles, 

 the clavicle, the first costal cartilage, and the remains of the thymus gland. 



Behind are the pleura and lung. 



To the right are the right pleura and lung and the phrenic nerve. 



To the left (fig. 509) are the right subclavian artery, the innominate artery, the right 

 vagus nerve, and the trachea. 



The left innominate vein [v. anonyma sinistra] (fig. 509) measures 6 to 7.5 cm. 

 (2| to 3 in.) in length, and extends from its origin behind the sternal end of the 

 left clavicle obliquely across the three main branches of the arch of the aorta, to 

 unite with the right innominate vein behind the cartilage of the first rib close to 

 the sternum to form the vena cava superior. In this course it runs from left 

 to right with an inclination downward and slightly backward. A line drawn 

 obhquel}^ across the upper half of the manubrium of the sternum, from the sterno- 



