428 THE SUBCLAVIAN ARTERIES. 



upper six intercostal nerves, in front ; it lies at first upon the pleura, but lower down 

 it is separated therefrom by the triangularis sterni muscle. This artery has two 

 companion veins, which are united into a single trunk at the upper part of the chest. 

 Branches. (a) The superior phrenic artery or comes nervi phrenici, a long 

 slender branch, arises from the artery at the upper part of the thorax, and descends, 

 in company with the phrenic nerve, between the pleura and pericardium, to the 

 diaphragm. It gives small offsets to the pericardium ; and its terminal branches 

 supply the fore part of the diaphragm and anastomose with the inferior phrenic 

 (from the aorta) and musculo-phrenic arteries. 



(b) The mediastinal branches, of very small size, ramify in the loose connective 

 tissue of the mediastinal space, and supply the thymus body or its remains. 

 Pericardial branches are given off to the pericardium ; and branches named sternal 

 are supplied to the triangularis sterni muscle, and to the posterior surface of the 

 sternum. These small vessels form with offsets from the superior phrenic, bronchial, 

 and intercostal arteries a fine wide-meshed network beneath the pleura, to which 

 Turner has given the name of subpleural mediastinal plexus. 1 



(c) The anterior intercostal arteries, two in each of the upper six spaces, arise 

 from the internal mammary, either separately, or by a trunk common to the two, 

 which soon divides. The arteries pass outwards, at first between the pleura and the 

 internal intercostal muscles, and afterwards between the two layers of intercostals ; 

 they lie, one near the upper and one near the lower rib, and inosculate with the 

 corresponding branches derived from the aortic intercostals. These branches supply 

 the jnjbercostal and pectoral muscles, and give some offsets to the mamma and 

 integument. 



(d) The anterior or perforating branches pass forwards through the upper six 

 iatercostal spaces, and turning outwards ramify partly in the pectoralis major, and 

 partly in the integument on the front of the chest. Those placed nearest to the 

 mammary gland supply that organ, and in the female they are of comparatively 

 large size, especially during lactation. Some small offsets ramify on the sternum. 



(e) The musculo-phrenic artery, the outer of the two branches into which the 

 internal mammary divides, inclines downwards and outwards behind the cartilages of 

 the false ribs, perforating the attachment of the diaphragm, and becoming gradually 

 reduced in size as it reaches the tenth cartilage. It gives branches backwards into 

 the diaphragm ; others, which pass outwards to form the anterior intercostals of the 

 seventh, eighth and ninth spaces, and are disposed like those which are derived 

 higher up from the main trunk ; and some which descend into the abdominal 

 muscles. 



(/) The abdominal branch, or superior epigastric artery, descends between the 

 sternal and costal portions of the diaphragm into the wall of the abdomen, where it 

 lies at first behind the recbus, between the muscle and its sheath ; afterwards, 

 entering the muscle, the artery terminates in its substance, and anastomoses with 

 the epigastric artery from the external iliac. It supplies branches to the broad 

 muscles of the belly, to the skin, and to the diaphragm ; one offset runs forwards 

 upon the front of the ensiform process, and anastomoses with that of the opposite 

 side ; and small twigs pass backwards into the falciform ligament of the liver and 

 form communications with the hepatic artery. 



Varieties. The internal mammary artery is sometimes found connected at its origin with 

 the thyroid axis, or with one or both of the scapular arteries these being detached from the 

 thyroid. It occasionally springs from the second or third part of the subclavian artery, the 

 latter being the more frequent position of the two. In very rare instances it has been found 



1 Brit, and For. Med. Chir. Rev., Jan., 1865. 



