402 THORACIC AORTA. 



They are distributed to the walls of the thorax, and to the viscera con- 

 tained within it the latter being much the smaller and least numerous 

 branches. 



A. The branches to the viscera are very irregular in their number and 

 place of origin. They are as follows. 



The pericardiac branches are some very small and irregular vessels which 

 pass forwards and ramify on the pericardium. 



THE BRONCHIAL ARTERIES are the proper nutritious arteries of the sub- 

 stance of the lung: they accompany the bronchial tubes in their ramifications 

 through that organ, and they also supply the bronchial glands, and in part 

 the oesophagus. These vessels vary frequently in number, and in their 

 mode of origin. The bronchial artery of the right side arises from the first 

 aortic intercostal artery, or by a common trunk with the left bronchial 

 artery from the thoracic aorta ; on the left side there are generally two 

 bronchial arteries, both of which arise from the thoracic aorta, one near the 

 commencement of that trunk, and the other, named inferior bronchial, 

 luwer down. Each artery is usually directed to the back part of the 

 corresponding bronchus, along which it run, dividing and subdividing with 

 the successive bronchial ramifications in the substance of the lung. 



Peculiarities of the bronchial arteries. The place of origin is liable to much 

 variation. The artery of the right side has been found to arise singly from the aorta, 

 from the internal mammary, or from the inferior thyroid. The bronchial arteries of 

 the two sides have been seen to arise by a common trunk from the subclavian. (Haller.) 

 Two common trunks, each furnishing a branch to the right and left lungs, have been 

 observed in a single case to descend into the thorax after arising, one from the 

 internal mammary, and the other from the superior intercostal artery. (R. Quain, 

 pi. 26, f. 5.) Instances occur of two distinct bronchial arteries for each lung. 



THE CEsofHAGEAL ARTERIES are variable in size and number. There are 

 usually four or five, which arise from the fore part or right side of the 

 aorta, and run obliquely downwards upon the oesophagus, supplying its 

 coats. 



Their lower branches anastomose with the ascending offsets of the coronary artery 

 of the stomach, while their upper branches communicate with those of the inferior 

 thyroid artery. 



Posterior mediastinal branches of the aorta, small and irregular, supply 

 the glands and loose tissue of the posterior mediastinum. 



B. The branches furnished by the aorta to the walls of the thorax are 

 named intercostal from their distribution. 



THE INTERCOSTAL ARTERIES arise from the posterior part of the aorta, 

 and run outwards upon the bodies of the vertebrae, to reach the intercostal 

 spaces. They are usually ten in number the upper intercostal space, and 

 occasionally also the second, being supplied by the superior intercostal 

 branch of the subclavian artery. Owing to the position of the aorta to the 

 left side of the spine, the right aortic intercostals cross over the front of 

 the vertebrae, furnishing small branches to their interior, and are longer 

 than the arteries of the left side. The vessels of both sides pass outwards 

 behind the pleura, and are crossed by the sympathetic nerve : those of the 

 right side also pass behind the oesophagus, the thoracic duct, and the azygos 

 vein. 



In each intercostal space the artery, passing outwards more hori- 

 zontally than the ribs, crosses the space obliquely, so as to gain the 

 lower border of the upper rib near its angle. It lies upon the deep 

 surface of the external intercostal muscle, and in the back of the space 



