FORM OF THE AORTIC ARCH. 335 



veins of the right side ; g, kidney, g f suprarenal body ; h, body of the fourth lumbar 

 vertebra. 



/, sinus of the aortic arch, or ascending part of the arch : below this the semilunar 

 valves are seen closed and distended by injection ; /', posterior part of the arch, upon 

 which the left pneumogastric nerve is seen descending ; 1", descending thoracic part of 

 the aorta ; II, abdominal aorta emerging from between the crura of the diaphragm and 

 descending to near its termination. 



Branches of the arch and thoracic aorta ; 1, right and left coronary arteries ; 2, inno- 

 minate ; 3, left carotid ; 4, left subclavian ; 5, bronchial arteries ; 6, 6, cesophageal 

 arteries : the lower figure points by a line to the thoracic duct ; 7, intercostal arteries, 

 marked in the sixth and seventh intercostal spaces. 



Branches of the abdominal aorta ; 8, inferior diaphragmatic arteries cut short ; 9, 

 cceliac axis with the gastric, splenic, and hepatic arteries cut short ; 10, placed on the 

 aorta below the superior mesenteric artery (cut short) and the origin of the renal arteries ; 

 a little below this the origin of the spermatic arteries ; below //, the inferior mesenteric 

 artery, 11, 11, two of the lumbar arteries. 



Branches of the carotid arteries ; the greater part of the right carotid artery has been 

 removed to show the ascent of the vertebral artery in the canal of the transverse pro- 

 cesses ; + is placed between the vertebral artery and the recurrent laryngeal nerve ; 3', 

 internal carotid artery ; 4, commencement of the external carotid artery ; close to this 

 the superior thyroid artery is given off, which is seen descending to the larynx and 

 thyroid body ; 5, the lingual and facial arteries ; 6, continuation of the external 

 carotid, &c. 



Branches of the subclavian arteries ; on the right side the middle part of the scalenus 

 anticus muscle is removed ; on the left the figure 4 is placed close to the origin of the 

 four following vessels ; 5, vertebral ; 6, internal mammary ; 7, thyroid axis ; 7', its 

 suprascapular branch ; 7", its transverse cervical branch ; 8, superior intercostal artery, 

 supplying two spaces on the right side and one on the left, rising in common with the 

 deep cervical which turns upwards behind the subclavian artery ; 9, a posterior scapular 

 artery rising from the third part of the subclavian. 



of the second dorsal vertebra. Arrived at that point, it bends downwards, 

 iu dining, at the same time, a little towards the middle line ; and at the 

 lower border of the body of the third dorsal vertebra, on its left side, the 

 arch terminates in the descending portion of the vessel. At its origin, the 

 arch of the aorta is larger than elsewhere, and presents externally three 

 small bulgings of nearly equal size, corresponding with the dilatations 

 which form the sinuses of Valsalva or of the aortic valves, already described 

 with the heart. Two of these sinuses are placed anteriorly and one 

 posteriorly, and in the two anterior sinuses are seen the orifices of the two 

 coronary arteries of the heart, the first branches given off by the aorta. 



From the difference in the direction and connections of different portions 

 of the arch it is described as consisting of an ascending, a transverse, and a 

 descending portion. 



The ascending portion of the arch of the aorta is placed at its commence- 

 ment behind the sternum, on a level with the lower border of the third 

 costal cartilage of the left side ; and it rises as high as the upper border of 

 the second costal cartilage of the right side. Its length is about two inches 

 or two inches and a quarter ; and its direction is curved. 



In most cases there exists along the right side a dilatation, named the 

 great sinus of the aorta. This dilatation varies in size in different bodies, 

 and occasionally is not to be detected. 



This portion of the aortic arch is enclosed in the pericardium, and, 

 together with the pulmonary artery, is invested by a fold of the serous 

 layer of that bag, in such a manner that both vessels are covered by the 

 serous membrane, except where they are in contact with each other. 



At its commencement the ascending part of the arch is concealed by the 

 pulmonary artery, and by the right auricular appendage which overlaps it ; 

 but, further up, the aorta passes to the right side and the pulmonary artery 



