268 THE VASCULAR SYSTEMS 



Relations. /// front, root of the left lung, pericardium, and 

 esophagus; behind, azygos minor vein and spinal column; to flu; 

 left, left lung and pleura, and, below the esophagus; to the right 

 esophagus above, vena azygos major, thoracic duct. 



The branches of the thoracic aorta : 



(a) The PERICARDIAC. 



(b) The BRONCHIAL, to the bronchial glands and the esophagus ; 

 they are also the nutrient vessels of the lung. The right some- 

 times arises from the first aortic intercostal. 



(c) Four or five ESOPHAGEAL, joining the inferior thyroid 

 above, the gastric and phrenic below. 



(d) The POSTERIOR MEDIASTINAL. 



(e) The INTERCOSTAL. These are nine or ten, the superior 

 intercostal from the subclavian supplying the upper space or 

 two. They cross obliquely to the edge of the rib above, running 

 at first on the external, and then between the two sets of inter- 

 costal muscles. 



Each divides into two branches running along the contiguous 

 borders of the two ribs, and each uniting anteriorly with the 

 corresponding branch of the anterior intercostals from the 

 internal mammary. 



A posterior branch runs from each, and divides into a spinal 

 branch to the cord and a muscular branch. 



The Abdominal Aorta 



The abdominal aorta runs from the last dorsal to the left side 

 of the middle of the body of the fourth lumbar vertebra, there 

 dividing into the two common iliacs. 



Relations. In front, lesser omentum, stomach, pancreas, trans- 

 verse duodenum, left renal and splenic veins, peritoneum form- 

 ing mesentery, aortic, and solar plexuses ; behind, receptaculum 

 chyli, thoracic duct, left lumbar veins, and spine; to the right, 

 crus of the diaphragm, vena cava, great azygos vein, thoracic 

 duct, right semilunar ganglion, splanchnic nerve; to the left, 

 splanchnic nerve, left semilunar ganglion. 



The branches of the abdominal aorta : 



(a) Parietal and (b) visceral. 



The parietal branches are: I. The phrenic, a right and a 

 left. Their origin is inconstant, from the aorta separately or 

 in common, or from one of its branches. They run across the 



