THE ASCENDING AORTA. 



381 



ASCENDING AORTA. 



The ascending aorta (28 mm.) arises from the upper and fore part of the base of 

 the left ventricle of the heart, under cover of the upper end of the infundibulum of 

 the right ventricle. At its commencement it is placed behind the left half of the 

 sternum, on a level with the lower border of the third costal cartilage. Thence it 

 passes upwards and to the right side somewhat in the direction of the heart itself, 

 but at the same time approaching nearer to the sternum, and gains the right border 

 of that bone opposite the attachment of the second costal cartilage. At this spot 

 the vessel changes its course, taking a direction backwards and to the left, and the 



Fig. 331. THE HEART AND GREAT SYSTEMIC VESSELS, 

 FROM BEFORE. (R. Quain.) 



The pulmonary artery has been cut short close to its 

 origin in order to show the first part of the aorta. 

 1, right ventricle ; 2, left ventricle ; 3, root of pulmon- 

 ary artery ; 4 4', arch of the aorta ; 4", descending 

 thoracic aorta ; 5, right, and 6, left auricular appendix ; 

 7, 7', innominate veins, joining to form the superior 

 vena cava ; 8, inferior vena cava ; 9, one of the 

 hepatic veins ; + , placed in the right auriculo-ventri- 

 cular groove, points to the right coronary artery ; 

 + +, placed in the anterior interventricular groove, 

 points to the descending branch of the left coronary 

 artery. 



arch is considered to begin. The length of 

 the ascending aorta is about two inches or 

 two inches and a quarter, and it describes 

 a slight curve with its concavity upwards, 

 backwards, and to the left. Near the base 

 of the heart the aorta is enlarged, and pre- 

 sents externally three small bulgings of 

 nearly equal size, corresponding with the 

 dilatations which form the sinuses of Yal- 

 salva., described with the heart. These sinuses 

 are placed, one in front and two behind, and 

 from the anterior and left posterior are given 

 off the two coronary arteries of the heart. 



In most cases there is also along the right side of the ascending aorta and the 

 beginning of the arch another dilatation called the great sinus of the aorta. This 

 dilatation varies in size in different bodies, and occasionally is not to be detected : 

 it is commonly better marked in old persons. 



The ascending aorta is entirely covered by the fibrous pericardium, and is 

 enclosed with the pulmonary trunk in a common sheath of the visceral pericardium, 

 in such a manner that both vessels are invested by the serous membrane except 

 where they are in contact with each other. At its commencement it is concealed 

 anteriorly by the pulmonary trunk and the right auricular appendage ; but farther 

 up, as the aorta passes forwards and to the right side, and the pulmonary trunk 



parts called ascending, transverse and descendiny. But the first part diners so much from the rest of 

 the vessel in respect of its intrapericardial position and its origin from the foetal aortic bulb as to justify 

 its separation as a primary division of the trunk, whereas the third part is in no way marked off by dif- 

 ferences in direction, relations, or mode of development from the remainder of the descending trunk, and 

 the whole of the vessel which rests against the dorsal vertebrae, from the fourth onwards, is therefore 

 here described as the descending thoracic aorta, the name arch of the aorta being confined to the portion 

 passing backwards above the root of the lung. 



