192 



AORTA. 



terfere with the full distension of the auricles. 

 Aneurisms of the transverse portion of the 

 aorta, when directed forwards, usually project 

 at the right side of the sternum about the 

 second intercostal space : when the sac extends 

 upwards towards the neck, it frequently be- 

 comes a matter of extreme difficulty to dis 

 tinguish an aneurism of the aorta from an 

 aneurism of the irmominata or some other 

 large arterial trunk in the neighbourhood ; 

 cases are on record, where the pressure of such 

 aneurisms of the aorta caused obliteration of 

 the subclavian and common carotid. When 

 aneurisms extend backwards, they produce a 

 variety of effects, interfering with respiration 

 and deglutition from their pressure on the 

 trachea and oesophagus, sometimes producing 

 obliteration of the thoracic duct. The pres- 

 sure produced by aneurisms of the thoracic 

 and abdominal aorta occasionally cause ab- 

 sorption of the bodies of the vertebrae, and give 

 rise to an appearance not very dissimilar to 

 that produced by caries. 



Aneurisms of the arch of the aorta do not 

 so often terminate fatally by making their way 

 through the anterior parietes of the chest, and 

 opening externally as by bursting internally : 

 when they occur in that part of the arch of the 

 aorta covered by the pericardium, they most 

 usually burst into the sac of that membrane; 

 cases are recorded in which aneurisms of the 

 aorta have burst into the pulmonary artery,* 

 or, taking a direction backwards, have opened 

 into the trachea, oesophagus, or the substance 

 of the lungs. Aneurisms of the thoracic por- 

 tion of the aorta sometimes burst into the left 

 pleura, sometimes into the posterior medi- 

 astinum : they have been known to point at the 

 left side of the spine, after having caused ab- 

 sorption of the heads of the ribs and sides 

 of the bodies of the vertebrae. In two cases 

 observed by Laennec and Mr. Chandler, aneu- 

 rism of the thoracic aorta burst into the spinal 

 canal. Aneurisms of the abdominal aorta 

 most usually burst into the cellular tissue of 

 the lumbar regions behind the peritoneum, 

 seldom into the sac of that membrane. An 

 aneurism of the abdominal aorta has been 

 observed to make its way backwards by the 

 side of the spine, and point in such a situation 

 as to have been at first mistaken for lumbar 

 abscess. 



Branches of the aorta. I. Branches arising 

 from the arch. From the arch of the aorta 

 five branches are given off; two from its com- 

 mencement, the coronary arteries^ and three 

 vessels of considerable size (fig. 78 a b c), from 

 the upper part of its transverse portion to 

 supply the head and the upper extremities. 

 The coronary arteries of the heart or the car- 

 diac arteries arise from the aorta close to its 

 origin, and immediately above the free borders 

 of the sigmoid valves ; they are usually two in 

 number, one for each ventricle. 



The right, anterior or inferior coronary 

 artery is often larger, seldom smaller than the 



* Dr. Wells in Trans, of a Society for Improve- 

 ment of Medical and Surgical Knowledge, vol. iii. 



Fig. 78. 



A B, arch of the aorta. 



C, thoracic aorta. 



D, abdominal aorta. 



E, common iliac artery. 

 g, middle sacral artery. 



left; it arises from the anterior side of the 

 aorta above the anterior sigmoid valve, coming 

 out from between the roots of the aorta and 

 pulmonary artery, it passes downwards and to 

 the right, side in the groove between the right 

 auricle and ventricle, turns round the right edge 

 of the heart until it reaches the groove of the 

 septum on the inferior surface of that organ, 

 when it changes its direction, coursing along 

 that groove until it arrives at the apex of the 

 heart, where it anastomoses with the left coro- 

 nary artery ; in its course it gives off to the 

 right and left many tortuous branches arising 

 nearly at right angles, the right branches are 

 smaller and go to the right auricle, the left are 

 larger and belong to the right ventricle, which 

 they traverse in a longitudinal direction to- 

 wards its apex. From the origin of the right 

 coronary artery two small branches are given 

 off, one to the commencement of the pul- 

 monary artery and the surrounding fat, which 

 anastomoses behind the pulmonary artery 

 with a branch of the left coronary; the se- 

 cond branch anastomoses with the bronchial 

 arteries. 



The left posterior or superior coronary 

 artery arises between the left auricle and the 

 posterior surface of the pulmonary artery, de- 



