THE THORAX 931 



intercostal or sternal glands, which lie along the course of the 

 internal mammary' arter\\ 



Internal Mammary Artery. — ^This vessel arises from the lower 

 portion of the first part of the subclavian artery, and it passes down- 

 wards, forwards, and inwards behind the inner part of the clavicle 

 and the first costal cartilage. It then descends vertically behind 

 the succeeding costal cartilages as low as the sixth intercostal space, 

 where it terminates by dividing into two branches, namely, the 

 superior epigastric and the musculo-phrenic. The artery lies about 

 \ inch from the margin of the stermma. 



Cervical Relations — Anterior. — ^The clavicular portion of the 

 sterno-cleido-mastoid muscle, and the internal jugular and sub- 

 clavian veins. The phrenic nerve crosses it superficially from 

 without inwards. Posterior. — ^The dome of the pleura. 



Thoracic Relations — Anterior. — ^The pectoralis major ; upper six 

 costal cartilages ; anterior intercostal aponeuroses ; internal inter- 

 costal muscles ; and upper six intercostal nerves. Posterior. — ^The 

 pleura above, and subsequently the triangularis sterni muscle. 

 Lateral. — ^The artery has a vena comes on either side of it. The 

 anterior intercostal or sternal glands lie along the course of the 

 vessel. 



Branches. — The artery gives off no branches in the neck. In the 

 thoracic part of its course it furnishes the following branches : 



Superior phrenic. Anterior intercostal. 



Mediastinal. Perforating. 



Pericardial. Musculo-phrenic. 



Sternal. Superior epigastric. 



The superior phrenic artery, long and slender, arises high up, and 

 accompanies the phrenic nerve to the diaphragm, from which cir- 

 cumstance it is known as the comes nervi phrenici. It gives twigs to 

 the pericardium and pleura, and in the diaphragm it anastomoses 

 with the inferior phrenic branch of the abdominal aorta and with 

 the musculo-phrenic branch of the internal mammary. The 

 mediastinal branches are distributed to the contents of the anterior 

 mediastinum, namely, the remains of the thymus body, anterior 

 mediastiucd glands, and areolar tissue. The pericardial branches 

 supply the front part of the pericardium. The sternal branches are 

 distributed to the sternum and triangularis sterni muscle. The 

 anterior intercostal arteries are two in number to each of the 

 upper six intercostal spaces. For their description, see Index. 

 The perforating branches are six in number, one arising opposite 

 each of the upper six intercostal spaces. Each vessel pierces the 

 internal intercostal muscle, anterior intercostal aponeurosis, and 

 pectoralis major. Thereafter it gives a few twigs to the front of 

 the sternum, and then turns outwards to supply the pectoral integu- 

 nient. The second, third, fourth, and fifth perforating branches 

 give offsets to the inner portion of the mammary gland. ' 



The musculo-phrenic artery is one of the terminal branches of the 



