114 ANATOMY OF UPPER EXTREMITY, ETC. 



The superior vena cava will be seen entering the peri- 

 cardium and joining the upper part of the right auricle. 



The INFERIOR YENA CAVA enters the inferior part of the 

 right auricle as soon as it passes through the diaphragm 

 and pericardium, holding the root of the heart downward, 

 and giving the organ the oblique position peculiar to it. 



The PULMONARY VEINS are four in number, two for each 

 side; those upon the right side are longer than the others, 

 and emerge from the right lung in front of the pulmonary 

 artery; they pass beneath the inferior vena caA^a and enter 

 the left auricle. The two left pulmonary veins reach the 

 same cavity after a shorter course, passing in front of the 

 descending aorta. These vessels, though carrying arterial 

 blood, are called veins, because, like veins, they bring the 

 blood to the heart. 



The PULMONARY ARTERY ascending from the right ven- 

 tricle between the two auricles, overlies and partially con- 

 ceals the aorta; at about two inches from its commencement 

 it divides into the right and left pulmonary arteries; at the 

 point of division the remains of the ductus arteriosus will 

 be found as a fibrous cord extending from this vessel to the 

 aorta. The left pulmonary artery passes under the arch of 

 the aorta, and, emerging from the pericardium, enters the 

 left lung in front and a little above the left primary bron- 

 chus. The right artery passes in front of the descending 

 aorta, and enters the right lung in front and a little below 

 the right primary bronchus. These vessels, though carrying 

 venous blood, are called arteries, because, like arteries, they 

 carry the blood away from the heart. 



The ARCH OF THE AORTA commences at the anterior part 

 of the left ventricle ; emerging between the auricles and 

 behind the pulmonary artery, it ascends, turning gradually 

 to the left, and, passing through the pericardium, curves 

 ;Over the left primary bronchus, giving off the large vessels 

 for the head and arms, which will be studied in connection 

 with the neck (p. 56); it then passes downward into the 

 posterior mediastinum to become the descending aorta. 

 The portion just described is called the arch, from the 

 curved direction which it takes, and is divided into an 

 ascending, transverse, and descending portion. The ascend- 

 ing is the part within the pericardium ; the transverse that 

 from which the great vessels originate; and the descending 

 that portion intervening between the last of these vessels 



