188 



AORTA. 



the ventricle at three equidistant points by the 

 centres of their convex edges, where the fibres 

 of their marginal cord become intimately 

 blended with those of the tendinous ring of the 

 aortic opening of the ventricle ; between these 

 points are three triangular intervals, each of 

 which is occupied by a thin tendinous expansion 

 of considerable strength, having one of its sides 

 continuous with the tendon which encircles 

 the aortic opening of the ventricle, and the 

 other two continuous with the marginal ten- 

 dinous cord of the festooned commencement 

 of the middle tunic of the aorta. 



The convex margins of the sigmoid valves of 

 the aorta are attached to the margins of the 

 semilunar flaps, and are composed of thin ex- 

 pansions sent off from their marginal tendinous 

 cord, covered by a reflexion of the lining mem- 

 brane common to the heart and arteries. Hence 

 it follows that the fibres of the middle tunic 

 of the aorta are not continuous with the 

 muscular fibres of the ventricle, being sepa- 

 rated from them by the tendinous structure 

 above described ; this tendinous connexion is 

 strengthened and supported externally by a 

 layer of dense cellular membrane, which may 

 be regarded as the commencement of the 

 cellular or external tunic of the arterial 

 system. The lining membrane of the heart, 

 after being reflected over the sigmoid valves, 

 extends itself into the aorta, and becomes 

 continuous with the lining membrane of that 

 vessel. The muscular substance of the heart 

 rises in form of a swollen annular border 

 around the commencement of the aorta for a 

 little distance, and is connected to it by dense 

 cellular membrane. The serous layer of the 

 pericardium passes loosely from the surface 

 of the heart over the aorta; a quantity of 

 soft adipose substance, which is absent in the 

 foetus during the earlier months, begins to 

 collect under the serous membrane in this 

 situation, sometimes before, sometimes after 

 birth, and, increasing as life advances, is found 

 in considerable quantity in old age. The fore- 

 going description of the connexion of the aorta 

 with the heart has been determined by my own 

 dissections repeatedly performed, and agrees, in 

 its leading particulars, with the account given 

 of it by M. Beclard.* 



The aorta, arising from the left ventricle 

 of the heart opposite the left side of the body 

 of the fourth thoracic vertebra, ascends at first 

 obliquely forwards, and to the right behind the 

 middle bone of the sternum, until it arrives 

 at the right side opposite the second intercostal 

 space, and behind the sternal articulation of 

 the cartilage of the second rib ; it then stretches 

 backwards and to the left, opposite the junction 

 of the upper and middle portions of the ster- 

 num, on a level with the body of the second 

 thoracic vertebra, and curving downwards it 

 reaches the left side of the body of the third 

 thoracic vertebra, on which there is a slight 

 depression for lodging it; from this point it 

 descends through the posterior mediastinum, 



Diet, de Medenine, art. Aortc. Elemens 

 ci'Anat. Gent-rale, par Beclard. Paris, 1823. 



advancing in its course downwards from the 

 left side to the front of the bodies of the ver- 

 tebra ; it passes through the aortic opening of 

 the diaphragm, enters the abdomen, and on the 

 body of the fourth abdominal vertebra gives 

 off the two primitive iliac arteries, in which it 

 seems at first view to terminate; the aorta, 

 however, does not end here, but is continued, 

 although greatly reduced in size, under the 

 name of the middle sacral artery, as far as 

 the extremity of the os coccygis. 



The aorta is usually divided by anatomists 

 into three portions; the curved portion fiom 

 the heart to the third thoracic vertebra is called 

 the Arch of the aorta ; the remaining portion 

 of the vessel, to which the name of descending 

 aorta has been sometimes given, is called 

 Thoracic aorta above the diaphragm, and Ab- 

 dominal aorta below that muscle. 



The Arch of the aorta is divided into three 

 portions, for the purpose of describing its nu- 

 merous important relations to surrounding parts 

 with oreater accuracy ; these are, first, the 

 ascending or anterior limb ; second, the trans- 

 verse portion ; and, thirdly, the descending or 

 posterior limb. The commencement of the 

 aorta is covered anteriorly and to the left by 

 the pulmonary artery, on the right by the right 

 auricular appendage, the tip of which overlaps 

 it in front, and behind it rests on the sinus 

 of the left auricle. The ascending limb of the 

 arch lies first in front of the right pulmonary 

 artery, as that vessel crosses behind it in its 

 course to the right lung, and then it gets in front 

 of the right bronchus, and the cluster of bron- 

 chial glands which fill up the angle formed by 

 the bifurcation of the trachea ; it is bounded 

 on the right side by the superior vena cava, 

 and on the left by the pulmonary artery ; an- 

 teriorly it is separated from the sternum by the 

 anterior margins of both lungs, which here 

 approximate, and by the narrowest part of the 

 anterior mediastinum, where the attached sur- 

 faces of the opposite pleurae touch. This 

 portion of the aorta is contained within the bag 

 of the pericardium, the serous layer of which 

 invests it in every part except where it lies 

 in contact with the pulmonary artery. 



The transverse portion of the arch is shorter 

 than the ascending limb. The three great arte- 

 ries of the head and upper extremities arise 

 from its superior sides ; inferiorly it rests on the 

 left bronchial tube ; in front it has the cellular 

 membrane of the anterior mediastinum, the 

 thymus gland, and the inferior part of the vena 

 innominata ; behind it rests on the trachea a 

 little above its bifurcation, and on the left re- 

 current nerve. The posterior limb is the shortest 

 portion of the arch; it lies immediately behind 

 the division of the pulmonary artery, which 

 is connected to it by a ligament, the remains of 

 the ductus arteriosus; and it is crossed by the 

 left par vagum ; on the right side it is in con- 

 tact with the oesophagus, thoracic duct, and 

 left side of the body of the third thoracic ver- 

 tebra ; the rest of the circumference of the 

 thoracic aorta is covered by the left pleura, and 

 is in contact with the internal surface of the 

 left lung. In the generality of adults having 



