722 



HUMAN ANATOMY. 



conversely, would associate quite distinct vessels. It will be more convenient, there- 

 fore, to employ a topographic classification, according to which two main subdivi- 

 sions of the system — that of X[\it pulmonary aorta and that of the systemic aorta — may 

 be recognized, the systemic subdivision being again divided into the aortic arch, the 

 thoracic, and the abdominal portions . 



THE PULMONARY AORTA. 



The 

 monalis) 



ventricle. 



pulmonary aorta, most frequently termed the pulmonary artery (a. pul- 



takes its origin from the summit of the conus arteriosus of the right 



It is from 4.5-5 cm. (about 2 in.) in length, and is directed upward, 



backward, and slighdy towards the left, and beneath the arch of the aorta it divides 



into the right and left pulmonary arteries (Fig. 679). 



Fig. 679. 



Right innominate vein 



Left innominate vein 



I.eft common carotid artery 



/ ^ — • Left subclavian artery 



Left pulmonary artery 



Pulmonary veins 



Inferior 

 pulmonary veil. 



Stump of superior cava' 

 Right auricular appendage 



Aorta, systemic 

 Left coronary artery 

 Right coronary vessels 



Left auricular 

 appendage 



Conus arteriosus 

 ^Xy Interventricular branches 

 of left coronary vessels 



Left ventricle 



Right ventricle 



Injected heart and great vessels, viewed from before ; part of superior vena cava and aorta 

 have been removed to show right pulmonary artery. 



Relations. — Throughout the greater portion of its length the pulmonary aorta 

 is invested by that part of the visceral layer of the pericardium which surrounds it 

 and the basal portion of the systemic aorta. At its origin it is partly overlapped in 

 front by the tip of the right auricular appendix, and posteriorly it is in relation with 

 the base of the systemic aorta and the proximal portion of the right coronary artery. 

 More distally it lies to the left of the systemic aorta and rests upon the anterior sur- 

 face of the left auricle. * 



Branches. — The right pulmonary artery (ramus dexter) has an almost transverse course 

 from its origin towards the base of the right lung. It passes outward above the right auricle, 

 behind the ascending portion of the systemic aorta and the superior vena cava and in front of 

 the right bronchus. At the root of the lung it divides into three branches which are distributed 

 to the three lobes of the lung. 



The left pulmonary artery (ramus sinister) is somewhat shorter than the right, and passes 

 outward in front of the descending portion of the aortic arch and the left bronchus to the root 



