379 



VEINS OF THE TRUNK. 



The veins of the trunk may be divided into 1. The superior vena 

 cava, with its formative branches. 2. The inferior vena cava, with 

 its formative branches. 3 The azygos veins. 4. The vertebral and 

 spinal veins. 5. The cardiac veins. 6. The portal vein. 7. The 

 pulmonary veins. 



SUPERIOR VENA CAVA, WITH ITS FORMATIVE BRANCHES. 



Ven< Innominate. 



The Venae innominatce are two large trunks, formed by the union of 

 the internal jugular and subclavian vein, at each side of the root of the 

 neck. 



The Rigid vena innominata, about an inch and a quarter in length, 

 lies superficially and externally to the arteria innorainata, and descends 

 almost vertically to unite with its fellow of the opposite side in the 

 formation of the superior cava. At the junction of the jugular and 

 subclavian veins it receives from behind the ductus lymphaticus dexter, 

 and lower down it has opening into it the right vertebral, right internal 

 mammary and right inferior thyroid vein. 



The Left vena innominata, considerably longer than the right, ex- 

 tends almost horizontally across the roots of the three arteries arising 

 from the arch of the aorta, to the right side of the mediastinum, 

 where it unites with the right vena innominata, to constitute the supe- 

 rior cava. 



It is in relation in front with the left sterno-clavicular articulation 

 and the first piece of the sternum. At its commencement it receives 

 the thoracic duct which opens into it from behind, and in its course is 

 joined by the left vertebral, left inferior thyroid, left mammary, and by 

 the superior intercostal vein. It also receives some small veins from 

 the mediastinum and thymus gland. There are no valves in the venae 

 innominatae. 



SUPERIOR VENA CAVA. 



The superior cava is a short trunk about three inches in length, 

 formed by the junction of the two venae innominatae. It descends 

 perpendicularly on the right side of the mediastinum, and entering the 

 pericardium terminates in the upper part of the right auricle. 



It is in relation in front with the thoracic fascia, which separates it 

 from the thymus gland, and with the pericardium ; behind with the 

 right pulmonary artery, and right superior pulmonary vein ; internally 

 with the ascending aorta ; externally with the right phrenic nerve, and 

 right lung. Immediately before entering the pericardium it receives 

 the vena azygos major. 



