548 THE ARTERIES 



(3) The CESophageal arteries, four or sometimes five in number, arise at 

 intervals from the front of the thoracic aorta, the first coming off just below the left 

 lower bronchial. They usually increase in size from above downwards, the upper 

 coming olt" nn)re towards the right side of the aorta, the lower more towards the left 

 side. They i)ass forwards to the oesophagus, supplying that tu])e and anastomosing 

 with each other and with the descending oesophageal branches of the inferior 

 thvroid above, and Avith the ascending oesophageal branches of the phrenic and 

 gastric arteries below, thus forming a chain of anastomoses along the whole length 

 of the tube. 



B. Parietal Branches 



(1) The aortic intercostal arteries, usually ten in number on each side, 

 supply the lower intercostal spaces, the two upper spaces being supplied by the 

 superior intercostal branch of the subclavian artery. The tenth artery runs along 

 the lower l)order of the last rib, and would be better called the subcostal artery; 

 it is similar in its distribution to the other intercostals, but is described separately. 



The aortic intercostals arise in pairs from the back part of the thoracic aorta, 

 and at once turning, the one to the right, the other to the left, wind backwards 

 over the front and sides of the vertebral bodies to reach the intercostal spaces, 

 which they follow, and anastomose in front with the anterior intercostals given oflf 

 from the internal mammary and musculo-ijhrenic arteries respectively. In foetal 

 life these arteries run almost transversely backwards, or even with a slight inclina- 

 tion downwards, to the intercostal spaces; but after the first year, in conseciuence 

 of the disproportionate growth of the aorta and vertebral colunm, the upper inter- 

 costals have to ascend to reach their respective spaces. For convenience of descrip- 

 tion the intercostal arteries may be divided into two portions — the vertebral, which 

 lies upon the bodies of the vertebrae; and the intercostal, which lies in the inter- 

 costal spaces. 



The vertebral portion. — The arteries in their course round the vertebrse differ 

 on the two sides of the body. On the right side the arteries — and especially the 

 upper, in consequence of the aorta lying a little to the left side of the spine in the 

 upper part of its course — are longer than the left. They wind over the front and 

 right side of the vertebrse, being crossed by the thoracic duct and vena azygos 

 major, and covered by the right pleura and lung. The upper are also crossed by 

 the oesophagus. They give oflf small l:)ranches to the bodies of the vertel)ra^ and 

 anterior common ligament. On the left side, as the intercostals wind round the 

 sides of the bodies of the vertebrse, the lower are crossed by the vena azygos minor, 

 the two upper by the left superior intercostal vein, and the two next by the third 

 azygos vein when this is present. They are all covered by the left pleura and 

 lung. 



The intercostal portion. — In their course through the intercostal spaces the 

 arteries are alike on both sides. They at first cross the intercostal spaces ol;)liquely, 

 in consequence of the downward direction of the riljs, towards the angle of the rib 

 above, and thence are continued forward in the subcostal groove, and anastomose 

 with the superior branches of the anterior intercostals from the internal mammary 

 in the upper spaces, and from the musculo-phrenic in the loAver spaces. They lie 

 at first on the external intercostal muscles, being covered in front by the pleura and 

 lung, the endothoracic fascia and the infra-costales muscles. Opposite the heads of 

 the ribs they are crossed by the sympathetic nerve. At the angle of the ribs they 

 pass under cover of the internal intercostal muscles, and thence to their termination 

 lie between the two intercostal muscles. Their situation in the midspace as far as 

 the angle of the ril) should be remembered in performing paracentesis thoracis. To 

 avoid the risk of injuring the vessels, the puncture should not be made further 

 back than the angle of the ril;)S. They are accompanied by an intercostal nerve 

 and vein, the vein lying above and the nerve below, except in the upper si)aces 

 where the artery, having to ascend to reach the space, at first lies below the nerve 

 which passes transversely outwards. The uppermost aortic intercostal artery 

 anastomoses with the superior intercostal from the subclavian, and at times sup- 

 plies almost entirely the second intercostal space. The arteries to the tenth and 

 eleventh spaces on reaching the end of their respective ribs pass between the 



