THE PULMONARY VEINS. 



379 



upper aspect of this artery, a little to the left of the point of bifurcation of the main 

 trunk, a short fibrous cord, the ligamentum arteriosum, passes obliquely upwards 

 and backwards to join the under side of the aortic arch (fig. 309). This is the 

 remains of the dmtus arteriosm, which in the foetus forms the continuation of the 

 pulmonary trunk. 



In the root of the lung on both sides the pulmonary artery lies in front of the 

 bronchus, and behind the superior pulmonary vein. On the right side the bronchus 

 is higher than the artery ; while on the left the artery rises above the bronchus. 



The varieties of the pulmonary artery will be referred to along- with those of the aorta. 



PULMONARY VEINS. 



The pulmonary veins are four short trunks which convey the red blood from the 

 lungs to the left side of the heart, and which are found, two on each side, in the 

 root of the corresponding lung. On both sides the superior vein lies in front of, as 



Fig. 329. THE HEART AND GREAT VESSELS, 



FROM BEHIND. (R. Quahl.) | 



1, right, 2, left ventricle ; 3, right pul- 

 monary artery near the division of the main 

 trunk ; 3', branches of the right pulmonary 

 artery in the root of the right lung ; 3", the 

 same of the left ; 4', arch of the aorta ; 4", 

 descending thoracic aorta ; 5, right auricle ; 

 6, is placed on the division between the 

 right and left auricles ; 7, superior vena cava, 

 being joined by the large azygos vein ; 7', 

 left innominate vein ; 8, inferior vena cava ; 

 9, one of the hepatic veins ; 10, upper, 11, 

 middle (additional), and 12, lower right pul- 

 monary vein ; 13, upper, and 14, lower left 

 pulmonary vein ; + , + , branches of coro- 

 nary arteries. 



well as at a lower level than, the 



pulmonary artery ; while the inferior 



vein is placed farther back, and below 



the other constituents of the root. 



The two veins of the right side pass 



behind the superior vena cava and 



the right auricle, to enter the left auricle ; the upper vein receives one or more 



branches from the middle lobe of the right lung. The two left pulmonary veins 



pass in front of the descending aorta to reach the auricle. The pulmonary veins are 



joined, as they issue from the lung, by small anterior bronchial veins from the larger 



bronchia, the bronchial glands, and the back of the pericardium (Zuckerkandl). 



The length of the pulmonary veins is generally less than three-quarters of an inch, and 

 their diameter from 13 to 15 mm. Their relative size varies somewhat in different indi- 

 viduals, but usually the right upper is the largest, and the left upper the smallest of all. 

 Their capacity does not exceed that of the arteries, and indeed is said by some anatomists to 

 be rather less ; according to C. Krause the united sectional area of the four pulmonary veins 

 is to that of the right and left pulmonary arteries as 99 : 100. The pulmonary veins have 

 no valves. 



Varieties. The two veins of one side, more often the left, may unite into a common 

 trunk before entering the auricle. There is frequently a third smaller vein on the right 

 side, coming from the middle lobe of the lung. Other supernumerary veins are of rare 

 occurrence. The upper pulmonary vein of the right side has been seen opening into the 

 superior vena cava, that of the leit side into the left innominate vein. In one <nstance the 

 single right pulmonary vein was found joining the large azygos vein (F. J. Shepherd, Journ. 

 Anat., xxiv). 



