474 THE SUPERIOR VENA CAVA, 



the nnion of the subclavian with the internal juguhir vein at each 

 side, commence opposite the inner ends of the clavicles, and terminate 

 a little below the cartilac^e of the first rib on tlie right side, where, 

 by uniting, they form the upper vena cava. The right vein is very 

 short, and nearly vertical in its direction ; it is in apposition, on the 

 right side, with the pleura and the upper part of the right lung. The 

 vein of the left side, about three times longer than the right vein, 

 pursues a course from left to right, at the same time inclining some- 

 what downwards : it crosses behind th.o upper part of the first bone of 

 the sternum, separated from it by the sterno-hyoid and sterno-thyroid 

 muscles, and by the thymus gland or its remains ; it lies in front of the 

 three primary branches given off" from the arch of the aorta, and rests 

 upon the highest part of the arch. The innominate veins have no 

 valves. 



Lateral tributaries. — (a) The inferior thyroid veins emerge 

 from a venous plexus situated on the thyroid body — those of opposite 

 sides communicating by small branches across the trachea. The vein 

 of the left side descends in front of the trachea, behind the sterno- 

 thyroid muscles, and ends in the left brachio-cephalic or innominate 

 vein : that of the right side inclines outwards in some degree, and 

 opens into the corresponding brachio-ceplialic vein, or into the angle of 

 union between it and the vessel of the ojjposite side. In their course 

 these veins receive inferior laryngeal and tracheal branches. 



(b) The internal mammary veins follow exactly the course of the 

 arteries of the same name — two veins accompanying each of the arte- 

 ries. The two companion veins of the artery arise by small branches, 

 derived from the fore part of the walls of the abdomen, where they 

 anastomose with the epigastric veins ; from thence proceeding 

 upwards between the cartilages of the ribs and the pleura, they 

 receive the anterior intercostal veins which correspond with the 

 branches of the internal mammary artery, together with some small 

 diapJtragmatir, thipnic, and mediastinal veins, and these finally uniting 

 into a single trunk, each vein terminates in the brachio-cephalic of its 

 own side. 



(c.) The superior intercostal veins. — The right superior intercostal 

 vein receives the blood from the first two or three spaces, communi- 

 cating with the vessel in the space next below, and opens into the in- 

 nominate trunk of the same side, or into the vena cava. Frequently the 

 veins at the right side, corresponding with the superior intercostal 

 artery, pass downwards separately, to open into the azygos vein, as that 

 vessel arches forwards to join the upper vena cava : the separate vein 

 thus formed is inferior in size to that on the left side. The left superior 

 intercostal vein varies in length in different persons, being small when 

 the azygos minor is large, and ince versa. Usually it receives the veins 

 from tlie three or f )ur upper spaces, and is then directed forwards over 

 the left side of the spinal column and the aorta to open into the left in- 

 nominate vein. It receives in its course the left bronchial vein. The 

 left vein is sometimes directed downwards to join an azygos vein on its 

 own side. 



A small filjrous cord is frequently found joining the trunk of tlie superior 

 intercostal vein with tlae coronary sinus of the heart. This is the remains of 

 the left duct of Cuvier, a foetal structure to be afterwards described. 



