AORTA. 



193 



scending to the left between the left auricle 

 and pulmonary artery, and, having reached the 

 groove at the base of the heart, dividing into 

 two or three branches ; one anterior longitu- 

 dinal descends along the anterior groove of the 

 septum to the apex of the heart, where it anas- 

 tomoses with the termination of the right 

 coronary artery, with which it holds frequent 

 communication by branches which it sends 

 over the anterior surface of the right ventricle, 

 while it sends some large branches to the left 

 ventricle; this branch at its commencement 

 gives small twigs to the aorta and pulmonary 

 artery. The second branch of the left coronary 

 artery covered by the great coronary vein passes 

 from right to left in the groove between the 

 left auricle and ventricle, to both of which it 

 gives many branches, turns round the left 

 border of the heart, changes its direction, and 

 descends by the side of the right coronary 

 artery to the apex ; the third branch sinks into 

 the substance of the septum and continues its 

 course to the apex; this branch sometimes 

 arises directly from the aorta ; in this latter case, 

 of course, there will be three coronary arteries 

 arising from the aorta; Meckel has once seen 

 four ; the supernumerary coronary artery does 

 notarise above any particular valve, but usually 

 close to the origin of one of the normal 

 branches. It is rare to find but one coronary 

 artery in the human subject, which corresponds, 

 according to Camper, with the normal con- 

 formation in the elephant. The three large 

 branches arising from the transverse portion 

 of the arch of the aorta and sent to the head 

 and upper extremities, will be described in a 

 separate article. 



II. Branches of the thoracic aorta. These 

 may be divided into anterior and lateral. The 

 anterior branches are, the bronchial, cesophageal, 

 and posterior mediastinal. The lateral are the 

 inferior or aortic intercostal arteries. The 

 bronchial arteries are usually two in number, 

 one for each lung ; sometimes, however, there 

 are two for each lung, and sometimes the right 

 and left bronchial arise from a common trunk, 

 which usually springs from the first aortic in- 

 tercostal of the right side. 



The right bronchial artery most usually arises 

 from the first aortic intercostal artery of the 

 right side, which supplies it after having arrived 

 at the right side of the spinal column behind 

 the oesophagus, sometimes it comes direct from 

 the aorta; it proceeds in a tortuous course under 

 the right bronchus, to the root of the right lung, 

 after having given small branches to the oeso- 

 phagus, the pleura, the back part of the peri- 

 cardium and the bronchial glands. 



The left bronchial artery arises immediately 

 from the aorta and passes in front of the oeso- 

 phagus to the left bronchus, to the posterior 

 side of which it attaches itself. Both bronchial 

 arteries are similarly distributed through the 

 lungs, dividing with the bronchi, along each 

 branch of which they send two or more tortu- 

 ous twigs. The relation of the bronchial arte- 

 ries to the other vessels of the lungs will be 

 more particularly noticed in the article LUNG. 



The asophageal arteries vary in number from 



VOL. i. 



two to seven : they are inferior to the bronchial 

 in size : they arise from the front of the thoracic 

 aorta, and are distributed to the oesophagus, on 

 which they anastomose freely with descending 

 branches of the inferior thyroid from above, in 

 the middle of the oesophagus with the bronchial, 

 and below with branches of the phrenic and 

 coronary artery of the stomach, 



The posterior mediastinal arteries are nume- 

 rous and small; they send branches to the 

 oesophagus, thoracic aorta, thoracic duct, ab- 

 sorbents, and cellular membrane of the pos- 

 terior mediastinum, anastomosing with the 

 bronchial, oesophageal, and some branches of 

 the right thoracic intercostal arteries. 



Inferior or aortic intercostal arteries. Of 

 the eleven intercostal spaces the two superior are 

 mostly supplied with arteries from the superior 

 intercostal branch of the subclavian ; and as the 

 first aortic intercostal artery frequently supplies 

 the third arid fourth intercostal spaces, we often 

 meet with but eight pairs of intercostal arteries 

 coming immediately from the aorta (jig. 78, d). 

 The first right aortic intercostal is usually the 

 largest of the series in consequence of giving 

 origin to the right bronchial ; the size of the ifrter- 

 costal arteries diminishes in general from above 

 downwards. All the intercostal arteries arise 

 rather from the posterior part of the aorta, those 

 of opposite sides arising very near each other, 

 and sometimes springing from a common trunk. 

 At first they descend obliquely on the vertebral 

 column, at an acute angle to the trunk of the 

 aorta. The right intercostal arteries are longer 

 than the left, in consequence of the position of 

 the thoracic aorta on the left side of the spine. 

 Each artery is lodged at first in a groove on 

 the side of the body of each vertebra, enters the 

 intercostal space passing behind the ganglia of 

 the sympathetic nerve, and immediately divides 

 into two branches, one posterior or dorsal, the 

 other anterior or intercostal. The posterior 

 branch passes backwards through a space above 

 the neck of each rib and below the tran verse 

 process of the superior of the two vertebrse, with 

 which the head of the rib is articulated ; it 

 gives some branches to the bodies of the ver- 

 tebrae, and in passing the intervertebral hole 

 it sends branches inwards to the spinal cord, 

 which anastomose with the spinal arteries. The 

 continuation of the vessel is distributed to the 

 longissimus dorsi, sacro-lumbalis, and other 

 muscles along the side of the spine, as well as 

 to the integuments of the back. The ante- 

 rior or proper intercostal branch is usually 

 larger than the posterior, and traverses the 

 intercostal space. At first it is situated be- 

 tween the pleura and external intercostal 

 muscle, it shortly divides into two smaller 

 branches, a superior and an inferior, which get 

 between the two layers of intercostal muscles. 

 The inferior branch, usually the smaller, runs 

 forwards along the superior border of the in- 

 ferior rib, and passes obliquely over its surface 

 to the periosteum covering it. The superior 

 branch, larger than the former, enters a groove 

 in the lower edge of the superior rib, about its 

 angle, in company with the intercostal nerve, 

 and passes forwards between the two layers of 



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