468 



THE ARTERIES 



portion is the ventral aorta; the descending portion, part of the left dorsal aorta; 

 and the transverse portion, the fourth left aortic arch. Each portion requires a 

 separate description. 



The Ascending Portion of the Arch of the Aorta 



The ascending portion or ventral aorta ascends behind the sternum from the 

 upper part of the left ventricle of the heart, on a level with the lower border of 

 the third left costal cartilage, to the upper border of the second right costal carti- 

 lage at the junction of these cartilages Avith the sternum. It measures from two 

 to two and a quarter inches (5 '5 cm.), forming, as it ascends, a gentle curve, the 

 most prominent part of which, when the aorta is distended, is situated about 

 a cpiarter of an inch (6 mm.) from the sternum. It is enclosed for the greater 



Fig. 322. — Scheme of the Relations of the First Portion of the Arch of the Aorta. 



(Walsham.) 



I, at origin : II, a little higher up. 

 1 



RIGHT AURICLE 



RIGHT AURICULAR APPENDIX 



Pulmonary artery 



II 



RIGHT BRONCHUS 

 Right pulmonary artery 



Vena cava superior 



PERICARDIUM 



RIGHT PLEURA 



RIGHT LUNG 



Ltfl pulmonary artery 



Pulmonary artery 

 PERICARDIUM 



LEFT LUNG 



LEFT PLEURA 



REMAINS OF THYMUS GLAND 



- MANUBRIUM 



part of its length in the pericardium, being invested, together with the pulmonary 

 artery, in a connnon sheath formed' by the serous layer of that membrane. A 

 dilatation known as the great sinus of the arch of the aorta is often present 

 along the right side. Immediately above the heart the aorta presents three bulg- 

 ings, known as the sinuses of Valsalva; they are placed, two anteriorly, and one 

 posteriorly. From the anterior are derived the coronarv arteries of the heart. 

 (SeeHEAUT. ) 



Relations. — In front (fig. o22), it is over]ap])cd at its commencement by the 

 right auricular ap])en(lix and the pulmonary artery. Higlierup, as the pulmonary 

 artery and auricular ai)pen(lix diverge, it is separated from the manul)rium l)y the 

 pericardium, the remains of the thymus gland, and by the loose tissue and fat in 

 the superior mediastinum, and is here slightly overlap})ed by the right pleura and 

 by the edge of the right lung in full inspiration. The commencement of the coro- 

 nary arteries is also in front. 



