THORACIC AORTA 545 



convexity of the deep arch, and, coursing downwards in the centre of the second, 

 third, and fourth interosseous spaces on the interosseous muscles, terminate near 

 the clefts of the fingers liy anastomosing with the digital arteries from the superficial 

 arch. These vessels suitply the interosseous muscles and the bones, and the second, 

 third, and fourtli hitiihrirales. 



(4) The recurrent branches come off from the concavity of the arch, and 

 consist of two or three small vessels which run upAvards towards the wrist, and 

 anastomose above with the anterior liranch of the anterior interosseous, and later- 

 ally with the anterior radial and ulnar carpal arteries, forming the so-called anterior 

 carpal rete (fig. 859). 



(5) The posterior, communicating, or perforating, also usually three in 

 number, pass from the arch directly through the second, third, and fourth inter- 

 osseous spaces between the. two heads of the corresponding dorsal interosseous 

 muscle, and join the proximal ends of the metacarpal artery (first dorsal inter- 

 osseous), and the second and third dorsal interosseous arteries respectively. 



THE DESCEXDIXG, OR THORACIC AORTA 



The thoracic aorta (fig. 360) extends from the termination of the aortic arch 

 at the lower liorder of the body of the fifth thoracic vertebra to the lower border of 

 the body of the twelfth thoracic vertebra, where it passes through the aortic open- 

 ing in the diaphragm, and is thence continued under the name of the abdominal 

 aorta. It is at first situated a little to the left of the vertebral column, but as it 

 descends approaches the front of the column, at the same time following the back- 

 ward curve of the spine, and at its passage through the diaphragm is almost in the 

 middle line. It Hes in the posterior mediastinum, having the oesophagus at first 

 a little to the right of it, then in front of it, and just above the tenth thoracic 

 vertebra, where this tube pierces the diaphragm, a little to its left side. 



Relations. — In front it is crossed from above downwards by the root of the 

 left lung, by the oesophagus, which separates it from the pericardium and heart, 

 and by the diaphragm. 



Behind, it lies upon the lower seven thoracic vertebrae, and is crossed obliquely 

 opposite the seventh or eighth thoracic vertebra by the vena azygos minor, and 

 opposite the tifth or sixth vertebra by the third azygos vein, or by one or more 

 of the left intercostal veins. 



On the right side it has, above, the oesophagus, and lower down the right 

 pleura and lung. The vena azygos major and thoracic duct also lie to the right, 

 but on a somewhat posterior plane. 



On the left side it has the left lung and pleura above, and the oesophagus below. 

 The vena azygos minor and the third azygos vein are also to the left, but on a pos- 

 terior plane. 



Branches of the Thoracic Aorta 



Thp branches of the thoracic aorta may be divided into the visceral and the 

 parietal. The visceral are: — (1) The pericardiac; (2) the l)ronchial; and (3) the 

 (esophageal. The parietal are: — (1) The intercostal; (2) the subcostal; (3) 

 the diaphragmatic; and (4) the arteria aberrans. 



A. Viiccral Branchrs 



(1) The pericardiac — two or three small branches, irregular in their origin, 

 course, and (li.^tribution — jniss to the po.sterior surface of the pericardium to supply 

 that structure, and anastomose with the otlier pericardiac l)ranches. They give 

 small twigs to tlio jiosti-rior m«_'diastinal glands. 



(2) The bronchial arteries ( Hg. 324) supply the bronchi and the lung sub- 

 stance. They vary considerably in their origin, course, and distribution; they are 

 usually three in number — one on the right side, and two on the left. 



(a) The right bronchial generallv arises either from the first right aortic inter- 

 35 



