INTERCOSTAL ARTERIES. 337 



dium. On its left side it is covered throughout by -the pleura; and on its 

 right side are the oesophagus and the thoracic duct, though near the dia- 

 phragm the gullet is placed over the aorta. 



The branches of the vessel are distributed to the surrounding parts, and 

 are named from their destination bronchial, pericardial, cesophageal, medi- 

 astinal, and intercostal. 



a. The bronchial arteries supply the structure of the lungs, and adhere 

 to the posterior part of the bronchial tubes, on which they ramify (p. 336) ; 

 they give some twigs to the bronchial glands and the oesophagus. 



For the left lung there are two arteries (superior and inferior), which 

 arise from the front of the aorta at a distance from each other. 



The artery of the right lung arises in common with one of the left bron- 

 chial arteries (superior), or from the first intercostal artery of the right 

 side. 



Bronchial veins. A vein issues from the root of each lung, and ends 

 in the following manner : the right joins the larger azygos vein ; and the 

 left ends in the superior intercostal vein of its own side. 



b. The pericardial branches are some irregular twigs, which are fur- 

 nished to the posterior part of the cardiac bag. 



c. (Esophageal branches arise at different points of the aorta, and are 

 four or five in number. Kamifying in the gullet, the vessels anastomose 

 with one another ; above, they communicate with branches of the inferior 

 thyroid artery near the pharynx ; and below, with twigs of the coronary 

 artery of the stomach. 



d. Small mediastinal branches (posterior) supply the areolar tissue and 

 the glands in the interpleural space. 



e. The intercostal arteries are ten on each side ; nine are furnished to 

 the same number of lower intercostal spaces, whilst the last lies below the 

 twelfth rib : to the upper two spaces branches are supplied from the inter- 

 costal artery of the subclavian trunk. 



These small vessels arise from the posterior part of the aorta, and run 

 outwards on the bodies of the vertebrae, beneath the cord of the sympathe- 

 tic nerve, to the intercostal spaces, where each divides into an anterior and 

 a posterior branch. In this course the upper arteries have a somewhat 

 oblique direction ; and as the aorta lies on the left of the spine the right 

 vessels are the longest : the right also pass beneath the oesophagus, the 

 thoracic duct, and the azygos vein. Many twigs are supplied to the bodies 

 of the vertebrae. 



In the spaces bounded by the true ribs, the anterior branch, the larger 

 of the two, continues onwards between the muscular strata nearly to the 

 anterior third of the intercostal space, where it ends in two pieces, which 

 anastomose with the intercostal arteries of the internal mammary (p. 239). 

 At first the artery lies in the middle of the intercostal space, beneath the 

 pleura and a fascia from the internal intercostal muscle, and resting on the 

 external intercostal layer; but near the angle of the rib it ascends to the 

 upper boundary. Accompanying the artery are the intercostal vein and 

 nerve, the vein being commonly above, and the nerve below it ; but in 

 the upper spaces the nerve is, at first, higher than the artery. 



Below the true ribs the vessels are contained partly in the thoracic and 

 partly in the abdominal wall. Behind they have the same course and 

 connections as the higher intercostals ; but in the wall of the abdomen 

 they lie between the two deep muscles ; they will be noticed hereafter. 



Branches are furnished to the intercostal and abdominal muscles, and 

 22 



