380 



THE SYSTEMIC ARTERIES. 



SYSTEMIC ARTERIES. 

 THE AORTA. 



The aorla, the main trunk of the systemic arteries, is at its commencement 

 generally a little smaller than the pulmonary artery, but in old persons it becomes 

 rather larger than that vessel. Spriuging from the left ventricle of the heart, it 



Fig. 330. THE AOKTA, A, FROM BEFORE, 



B, FROM BEHIND, WITH THE ORIGINS 

 OF ITS PRINCIPAL BRANCHES. (R. 



Quain.) * 



1 2, ascending aorta ; at 1, where 

 the aorta has been separated from the 

 left ventricle, are seen the semilunar 

 valves in a closed condition, the sinuses 

 of Valsalva, and the origins of the right 

 and left coronary arteries ; at 2, is the 

 great sinus ; 2 3, arch of aorta ; 4, in- 

 nominate artery ; 5, left carotid ; 6, left 

 subclavian ; 7, 7, 7, indicate three out of 

 the series of intercostal and lumbar arte- 

 ries : the bronchial and oesophageal arte- 

 ries are also seen arising from the front 

 of the descending thoracic aorta ; 8, 8, 

 right and left renal arteries ; 9, 9, right 

 and left common iliac arteries ; 10, middle 

 sacral artery ; 11, one of the inferior 

 phrenic arteries; +, coeliac axis; 12, 

 gastric artery ; 13, hepatic ; 14, splenic ; 

 15, superior mesenteric ; 16, inferior me- 

 senteric ; 17, 17, right and left spermatic 

 arteries. 



arches over the root of the left 

 lung, descends along the verte- 

 bral column, and, after passing 

 through the diaphragm into the 

 abdominal cavity, ends opposite 

 the fourth lumbar vertebra, by 

 dividing into the right and left 

 common iliac arteries. In this 

 course the aorta forms a contin- 

 uous single trunk, which gradu- 

 ally diminishes in size from its 

 commencement to its termination 

 (from 28 to 17^mm.), and gives 

 off larger or smaller branches at 

 various points. It is divided 

 into the ascending aorta, the 

 short part which is contained 

 in the pericardium, the arch, 

 passing backwards to the spine, 

 the descending thoracic aorta, the 



comparatively straight part extending to the diaphragm, and the abdominal aorta 



below the diaphragm. 1 



1 It has been usual in English text-books to describe the arch of the aorta as extending from the 

 left ventricle of the heart to the lower border of the fifth dorsal vertebra, and being divided into three 



