438 



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 distended, about a quarter of an inch behind the posterior sur- 

 face of the sternum. A little above its commencement, it is somewhat enlarged, 



Fig. 272. The Arch of the Aorta and its Branches. 



Rt Vagus 

 fteurrtnt laryiyeal 



Lfft Tayui 

 Left TTirtnle 

 TlunteicJiuet 



Fig. 273. flan of du Bran/Jut 



3 1 



naaty 



and presents three small dilatations, called the sinuses of the aorta (sinuses of Val- 

 salva), 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. 



