THE INTERCOSTAL ARTERIES. 



455 



with the ascending offsets of the coronary artery of the stomach and with the 

 phrenic arteries, while their upper branches communicate with those of the inferior 

 thyroid artery. 



Posterior mediastinal branches, small and irregular, supply the glands, areolar 



Fig. 370. THE THORACIC AND GREATER 



PART OF THE ABDOMINAL AOUTA, 



&o. (Allen Thomson.) 1 



For the general description of this 

 figure, see p. 383. The following num- 

 bers indicate the branches of the aorta : 

 1, placed between the origins of the 

 right and left coronary arteries ; 2, 

 innominate ; 3, left carotid ; 4, left 

 subclavian ; 5, bronchial ; 6, 6, cesopha- 

 geal ; 7, 7, intercostal arteries (sixth and 

 seventh) ; 8, inferior phrenic ; 9, cceliac 

 axis; 10, below the superior inesenteric 

 and opposite the origin of the renal ar- 

 teries ; 11, 11, two of the lumbar arteries. 



tissue, and other structures in 

 the posterior mediastinum, as well 

 as the vertebral portion of the 

 diaphragm. 



B. Branches to the wall of 

 the thorax : 



The intercostal arteries 

 'iv)' 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 nine in number 

 the upper two spaces being 

 supplied by the superior inter- 

 costal branch of the subclavian 

 artery. Owing to the position of 

 the aorta on the left side of the 

 spine, the right aortic intercostals 

 cross over the front of the ver- 

 tebrae, 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 large 

 azygos vein. 



In each intercostal space the artery, passing outwards more horizontally 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 is [separated from the pleura only by a 

 thin fascia, but farther outwards it lies between the two layers of intercostal 

 muscles. Extending forwards in the subcostal groove of the upper rib, it finally 



