584 ANGIOLOGY 



of about 1.25 cm. from the margin of the sternum, and at the level of the sixth 

 intercostal space divides into the musculophrenic and superior epigastric arteries. 



Relations. It is directed at first downward, forward, and medialward behind the sternal 

 end of the clavicle, the subclavian and internal jugular veins, and the first costal cartilage, and 

 passes forward close to the lateral side of the innominate vein. As it enters the thorax the phrenic; 

 nerve crosses from its lateral to its medial side. Below the first costal cartilage it descends almost, 

 vertically to its point of bifurcation. It is covered in front by the cartilages of the upper six 

 ribs and the intervening Intercostales interni and anterior intercostal membranes, and is crossed 

 by the terminal portions of the upper six intercostal nerves. It rests on the pleura, as far as the 

 third costal cartilage; below this level, upon the Transversus thoracis. It is accompanied by a 

 pair of veins; these unite above to form a single vessel, which runs medial to the artery and ends 

 in the corresponding innominate vein. 



Branches. The branches of the internal mammary are: 



Pericardiacophrenic. Intercostal . 



Anterior Mediastinal. Perforating. 



Pericardial. Musculophrenic. 



Sternal. Superior Epigastric. 



The Pericardiacophrenic Artery (a. pericardiacophre?iica; a. comes nervi phrenici) 

 is a long slender branch, which accompanies the phrenic nerve, between the pleura 

 and pericardium, to the diaphragm, to which it is distributed; it anastomoses 

 with the musculophrenic and inferior phrenic arteries. 



The Anterior Mediastinal Arteries (aa. mediastinales anteriores; mediastinal arter- 

 ies) are small vessels, distributed to the areolar tissue and lymph glands in the 

 anterior mediastinal cavity, and to the remains of the thymus. 



The Pericardial Branches supply the upper part of the anterior surface of the 

 pericardium; the lower part receives branches from the musculophrenic artery. 



The Sternal Branches (rami sternales] are distributed to the Transversus thoracis, 

 and to the posterior surface of the sternum. 



The anterior mediastinal, pericardial, and sternal branches, together with some 

 twigs from the pericardiacophrenic, anastomose with branches from the intercostal 

 and bronchial arteries, and form a subpleural mediastinal plexus. 



The Intercostal Branches {rami intercostales; anterior intercostal arteries} supply 

 the upper five or six intercostal spaces. Two in number in each space, these small 

 vessels pass lateralward, one lying near the lower margin of the rib above, and the 

 other near the upper margin of the rib below, and anastomose with the intercostal 

 arteries from the aorta. They are at first situated between the pleura and the 

 Intercostales interni, and then between the Intercostales interni and externi. 

 They supply the Intercostales and, by branches which perforate the Intercostales 

 externi, the Pectorales and the mamma. 



The Perforating Branches (rami perforantes) correspond to the five or six inter- 

 costal spaces. They pass forward through the intercostal spaces, and, curving 

 lateralward, supply the Pectoralis major and the integument. Those which corre- 

 spond to the second, third, and fourth spaces give branches to the mamma, and 

 during lactation are of large size. 



The Musculophrenic Artery (a. musculophrenica) is directed obliquely downward 

 and lateralward, behind the cartilages of the false ribs; it perforates the dia- 

 phragm at the eighth or ninth costal cartilage, and ends, considerably reduced 

 in size, opposite the last intercostal space. It gives off intercostal branches 

 to the seventh, eighth, and ninth intercostal spaces; these diminish in size as the 

 spaces decrease in length, and are distributed in a manner precisely similar to the 

 intercostals from the internal mammary. The musculophrenic also gives branches 

 to the lower part of the pericardium, and others which run backward to the dia- 

 phragm, and downward to the abdominal muscles. 



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