THE INTERNAL MAMMARY ARTERY 567 



passes to the medial side of the artery into the corresponding vena innominata, 

 or occasionally on the right side into the vena cava superior direct. The artery 

 may be divided into two portions, the cervical and the thoracic. 



The cervical portion is covered by the sterno-mastoid muscle, subclavian vein, and internal 

 jugular vein, and is crossed obliquely, in the latero-medial direction, by the phrenic nerve. 

 It rests upon the pleura and courses around the upper part of the innominate vein. There 

 is no branch from this part of the artery. 



The thoracic portion lies behind the cartilages of the six upper ribs, and in the interspace 

 between the ribs has in front of it the pectorahs major and the internal intercostal muscles 

 and external intercostal Ugaments. Behind, it is in contact above with the pleura, but it is 

 separated from it lower down by shps of the transversus thoracis (triangularis sterni). On 

 the left side, the artery between the fourth and sixth ribs may be said to be in the anterior 

 mediastinum, the pleura here forming a notch for the heart. In the first, second, and third 

 spaces the artery, if wounded, can be easily tied; but in the fourth space the operation is at- 

 tended with more difficulty. The remaining spaces are so narrow that a portion of the cartilage 

 would have to be removed to expose the vessel. 



The branches of the internal mammary artery are: — (1) The pericardio- 

 phrenic; (2) the anterior mediastinal and thymic; (3) the bronchial; (4) the peri- 

 cardiac; (5) the sternal; (6) the anterior intercostals; (7) the perforating; (8) the 

 lateral costal; (9) the superior epigastric; and (10) the musculo-phrenic. 



(1) The pericardio-phrenic artery [a. pericaridiophrenica], is a long slender vessel which 

 comes off from the internal mammary just after it has entered the chest, and descends with 

 the phrenic nerve, at first between the pleura and innominate vein; then (on the right side) 

 between the pleura and the vena cava superior; and lastly, between the pleura and the pericardium 

 to the diaphragm, where it anastomoses with the other diaphragmatic arteries. It gives 

 branches both to the pleura and pericardium. 



(2) The anterior mediastinal and thymic arteries [aa. mediastinales anteriores et thymicse] 

 come off irregularly from the internal mammary. They are of small size, and supply the con- 

 nective tissue, fat, and lymphatics in the superior and anterior mediastina and the remains of 

 the thymus gland. 



(3) The bronchial branches [rami bronchiales] are often wanting. When present they are 

 supphed to the bronchi and the lower part of the trachea. 



(4) The pericardiac branches are distributed to the anterior surface of the pericardium. 



(5) The sternal branches [rami sternales] enter the nutrient foramina in the sternum, and 

 also supply the transversus thoracis (triangularis sterni). 



(6) The anterior intercostal branches [rami intercostales] (figs. 463, 478) — two in each of 

 the five or six upper intercostal spaces — run laterally from the internal mammary artery, 

 along the lower border of the rib above and the upper border of the rib below, and anastomose 

 with the corresponding anterior and collateral branches of the aortic intercostals. Each pair 

 of branches sometimes arises by a common trunk from the internal mammary, which in this case 

 soon divides into an upper and a lower branch, as above described. They lie at first between 

 the internal intercostal muscles and the pleura; afterward between the external and internal 

 intercostal muscles. They supply the contiguous muscles, the pectorahs major, and the ribs. 



(7) The perforating or anterior perforating branches [rami perforantes] — five or six in 

 number, one corresponding to each of the five or six upper spaces — come off from the front of 

 the internal mammary, between the superior and inferior anterior intercostals, and, perforating 

 the internal intercostal muscles, pass forward between the costal cartilages to the pectorahs 

 major, which they supply [rami musculares]. The terminal twigs perforate that muscle close 

 to ttie sternum, and are distributed to the integument [rami cutanei]. The second, third, and 

 fourth perforating supply the inner and deep surface of the mammary gland, and become 

 greatly enlarged during lactation [rami mammaria]. They frequently require hgation in 

 excision of the breast. 



(8) The lateral costal branch [ramus costales lateralis] is given off close to the first rib, and 

 descends behind the ribs just external to the costal cartilages. It anastomoses with the upper 

 intercostal arteries. This vessel is often of insignificant size, or absent. 



(9) The superior epigastric artery [a. epigastrica superior] (fig. 462), or medial terminal 

 branch of the internal mammary artery, leaves the thorax behind the seventh costal cartilage 

 by passing through the costo-xiphoid space in the diaphragm. It is the direct prolongation of 

 the internal mammary downward. In the abdomen it descends behind the rectus muscle, 

 between its posterior surface and its sheath, and, lower, entering the substance of the muscle, 

 anastomoses with the inferior epigastric, a branch of the external iliac. It gives off the following 

 small branches: — (a) The phrenic, to the diaphragm; (6) the xiphoid, which crosses in front of 

 the xiphoid cartilage, and anastomoses with the artery of the opposite side; (c) the cutaneous, 

 which perforate the anterior layer of the sheath of the rectus and supply the integuments; 

 (d) the muscular, to the rectus muscle, some of which perforate the rectus sheath laterally, and 

 are distributed to the oblique muscles; (e) the hepatic (on the right side only), which pass along 

 the falciform ligament to the fiver, and anastomose with the hepatic artery; (/) the peritoneal, 

 which perforate the posterior layer of the sheath of the rectus, and ramify on the peritoneum. 



(10) The musculo-phrenic artery [a. musculophrenica], or lateral terminal branch of the 

 internal mammary artery, skirts laterally and downward behind the costal cartilages of the 

 false ribs along the costal attachments of the diaphragm, which it perforates opposite the ninth 

 rib. It terminates, much reduced in size, at the tenth or eleventh intercostal space by anasto- 

 mosing with the ascending branch of the deep circumflex ihac artery. It gives off in its course 

 the following small branches: — (a) The phrenic for the supply of the diaphragm; ih) the an- 

 terior intercostals, two in number for each of the lower five or six intercostal spaces, are dis- 



