418 ARTERIES. 



The "bronchial arteries are the nutrient vessels of the lungs, and vary in number, 

 size, and origin. That of the right side arises from the first aortic intercostal, or, 

 by a common trunk with the leit bronchial, from the front of the thoracic aorta. 

 Those of the left side, usually two in number, arise from the thoracic aorta, one 

 a little lower than the other. Each vessel is directed to the back part of the 

 corresponding bronchus, along which they run, dividing and subdividing, upon 

 the bronchial tubes, supplying them, the cellular tissue of the lungs, the bronchial 

 glands, and the oesophagus. 



The cesophageal arteries, usually four or five in number, arise from the front of 

 the aorta, and pass obliquely downwards to the oesophagus, forming a chain of 

 anastomoses along that tube, with the oesophageal branches of the inferior thyroid 

 arteries above, and with ascending branches from the phrenic and gastric arteries 

 below. 



The posterior mediastinal arteries are numerous small vessels which supply the 

 glands and loose areolar tissue in the mediastinum. 



The Intercostal arteries arise from the back part of the aorta. They are usually 

 ten in number on each side, the superior intercostal space (and occasionally the 

 second one) being supplied by the superior intercostal, a branch of the subclavian. 

 The right intercostals are longer than the left, on account of the position of the 

 aorta to the left side of the spine ; they pass outwards, across the bodies of the 

 vertebrae, to the intercostal spaces, being covered by the pleura, the oesophagus, 

 thoracic duct, sympathetic nerve, and the vena azygos major; the left passing 

 beneath the superior intercostal vein, the vena a/ygos minor, and sympathetic. 

 In the intercostal spaces, each artery divides into two branches, an anterior or 

 proper intercostal branch ; and a posterior or dorsal branch. 



The anterior branch passes outwards, at first lying upon the External inter- 

 costal muscle, covered in front by the pleura, and a thin fascia. It then passes 

 between the two layers of Intercostal muscles, and, having ascended obliquely 

 to the lower border of the rib above, divides, near the angle of that bone, into 

 two branches ; of these, the larger runs in the groove, on the lower border of 

 the rib above: the smaller branch along the upper border of the rib below ; passing 

 forward, they supply the Intercostal muscles, and anastomose with the anterior 

 intercostal branches of the internal mammary, and with the thoracic branches of 

 the axillary artery. The first aortic intercostal anastomoses with the superior 

 intercostal, and the last three pass between the abdominal muscles, inosculating 

 with the epigastric in front, and with the phrenic and lumbar arteries. Each 

 intercostal artery is accompanied by a vein and nerve, the former being above, 

 and the latter below, except in the upper intercostal spaces, where the nerve is at 

 first above the artery. The arteries are protected from pressure during the action 

 of the Intercostal muscles, by fibrous arches thrown across, and attached by each 

 extremity to the bone. 



The posterior or dorsal branch of each intercostal artery passes backwards 

 to the inner side of the anterior costo-transverse ligament, and divides into a 

 spinal branch, which supplies the vertebrae, and the spinal cord and its membranes, 

 and a muscular branch, which is distributed to the muscles and integument of the 

 back. 



THE ABDOMINAL AOETA (fig. 222). 



The Abdominal Aorta commences at the aortic opening of the Diaphragm, in 

 front of the body of the last dorsal vertebra, and, descending a little to the left 

 side of the vertebral column, terminates on the left side of the body of the fourth 

 lumbar vertebra, where it divides into the two common iliac arteries. As it lies 

 upon the bodies of the vertebrae, it is convex forwards, the greatest convexity 

 corresponding to the third lumbar vertebra, which is a little above and to the left 

 side of the umbilicus. 



