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ARTERIES. 



ASCENDING PART OF THE ARCH. 



The ascending portion of the arch of the aorta is about two inches in length. 

 It commences at the upper part of the left ventricle, in front of the left auriculo- 

 ventricular orifice, and opposite the middle of the sternum on a line with its 

 junction to the third costal cartilage ; it passes obliquely upwards in the direction 

 of the heart's axis, to the right side, as high as the upper border of the second 

 costal cartilage, describing a slight curve in its course, and being situated, when 



Fig. 205. The Arch of the Aorta and its Branches. 

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distended, about a quarter of an inch behind the posterior surface of the sternum. 

 A little above its commencement, it is somewhat enlarged, and presents three small 

 dilatations, called the sinuses of the aorta (sinuses of Valsalva) opposite to which 

 are attached the three semilunar valves, which serve the purpose of preventing 

 any regurgitation of blood into the cavity of the ventricle. A section of the aorta 

 opposite this part has a somewhat triangular figure ; but below the attachment of 

 the valves it is circular. This portion of the arch is contained in the cavity of 

 the pericardium, and, together with the pulmonary artery, is invested in a tube 

 of serous membrane, continued on to them from the surface of the heart. 



