BKANCHES OF THE SUBCLAVIAN ARTEEY. 913 



ircumflex scapular and with branches of the descending branch of the transverse 

 srvical artery. 



(3) Arteria Mammaria Interna. The internal mammary artery (Figs. 757, 761) 

 rises from the lower and anterior part of the subclavian, at the medial border 

 f the scalenus anterior and immediately below the origin of the thyreo-cervical 

 runk. It terminates, behind the medial extremity of the sixth intercostal space, 

 y dividing into the musculo-phrenic and the superior epigastric arteries. 



The artery passes at first downwards, forwards, and medially, lying upon the 

 leura, and behind the innominate vein, the sternal extremity of the clavicle, and 

 he cartilage of the first rib ; it is crossed obliquely, from the lateral to the 

 ledial side, by the phrenic nerve, which usually passes anterior to it. From the 

 artilage of the first rib it descends vertically, about 12 mm. (half an inch) from the 

 order of the sternum, and lies, in the upper part of its course, in front of the pleura, 

 ud, in the lower part, in front of the transversus thoracis muscle. It is covered 

 nteriorly by the cartilages of the upper six ribs, the intervening intercostal muscles, 

 nd the terminal portions of the intercostal nerves; and it is accompanied by 

 wo venae cornites, which unite together above, and on its medial side, to form a 

 ingle trunk which terminates in the innominate vein. 



Branches. (a) The pericardiaco-phrenic (O.T. comes nervi phrenic!) is a long slender 

 ranch which is given off from the upper part of the internal mammary. It accompanies 

 tie phrenic nerve, through the superior and middle mediastina, to the diaphragm, where 

 ; anastomoses with the inferior phrenic and musculo-phrenic arteries. In its course 

 ownwards this branch gives off numerous small rami to the pleura and pericardium, 

 rhich anastomose with offsets of the mediastinal and pericardial branches of the aorta 

 nd internal mammary arteries, and also with the bronchial arteries, forming the wide- 

 leshed subpleural plexus of Turner. 



(6) Anterior mediastinal branches, small and numerous, pass to the areolar tissue of 

 he anterior mediastinum and supply the areolar tissue and the sternum. 



(c) Thymic. Small twigs which supply the thymus. 



(d) Bronchial. One or several small branches which pass to the lower end of the 

 rachea and to the bronchi. 



(e) The intercostal are two in number in each of the upper six intercostal spaces, 

 'hey pass laterally and, for a short distance, they lie either between the pleura and the 

 iternal intercostal muscles or between the transversus thoracis and the internal inter- 

 ostal muscles ; they then pierce the internal intercostal muscles, and ramify between them 

 nd the external intercostal muscles, anastomosing with the aortic and superior intercostal 

 rteries and their collateral branches. 



(/) The perforating branches, one in each of the upper six intercostal spaces, are small 

 essels which pass forwards, with the anterior branches of the thoracic nerves, piercing 

 be internal intercostal muscle, the anterior intercostal membrane, and the pectoralis 

 lajor. They terminate in the skin and subcutaneous tissue. They supply twigs to the 

 ternum, and those in the third and fourth spaces, usually the largest of the series, give 

 ff branches to the mammary gland. 



(g) The musculo-phrenic, or lateral terminal branch of the internal mammary 

 rtery, runs downwards and laterally, from the sixth intercostal space to the tenth costal 

 artilage. In the upper part of its course it lies upon the thoracic surface of the 

 iaphragm, but it pierces the diaphragm about the level of the eighth costal cartilage, and 

 srminates on its abdominal surface. Its branches are : 



(i.) Muscular, which supply the diaphragm and anastomose with the superior and inferior 

 hrenic arteries. 



(ii.) Intercostal branches, two in each of the seventh, eighth, and ninth intercostal spaces ; 

 bey are distributed in the same manner as the corresponding branches of the internal mammary 

 rtery, and terminate by anastomosing with the aortic intercostals and tlieir collateral branches. 



(h) The superior epigastric, or medial terminal branch of the internal mammary artery, 



1 escends into the anterior wall of the abdomen. It leaves the thorax, between the sternal 



nd costal origins of the diaphragm, and enters the sheath of the rectus abdominis 



luscle, lying first behind, and then in the substance of the muscle. It terminates by 



nastomosing with branches of the inferior epigastric artery. Its branches are : 



(i.) Muscular, to the rectus, to the flat muscles of the abdominal wall, and to the diaphragm. 



(ii.) Anterior Cutaneous. Small branches which pierce the rectus abdominis muscle and 



be anterior portion of its sheath. They accompany the anterior terminal branches of the lower 



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