320 INTERNAL MAMMARY ARTERY. 



complexus and semi-spinalis colli muscles. It inosculates above with 

 the princeps cervicis of the occipital artery, and below, by a descending 

 branch, with the posterior scapular. 



The SUPERIOR INTERCOSTAL ARTERY descends behind the pleura 

 upon the necks of the first two ribs, and inosculates with the first aortic 

 intercostal. It gives off two branches which supply the first two in- 

 tercostal spaces. 



The INTERNAL MAMMARY ARTERY descends by the side of the 

 sternum, resting upon the costal cartilages, to the diaphragm ; it then 

 pierces the anterior fibres of the diaphragm ; and enters the sheath of 

 the rectus, where it inosculates with the epigastric artery, a branch of 

 the external iliac. In the upper part of its course it is crossed by the 

 phrenic nerve, and lower down lies between the triangularis sterni and 

 the internal intercostal muscles. 



The Branches of the internal mammary are, 



Anterior intercostal, 



Mammary, 



Comes nervi phrenici, 



Mediastinal, 



Pericardiac, 



Musculo-phrenic. 



The Anterior intercostals supply the intercostal muscles of the front 

 of the chest, and inosculate with the aortic intercostal arteries. Each 

 of the first three anterior intercostals gives off a large branch to the 

 mammary gland, which anastomoses freely with the thoracic branches 

 of the axillary artery ; the corresponding branches from the remaining 

 intercostals supply the integument and pectoralis major muscle. There 

 are usually two anterior intercostal arteries in each space. 



The Comes nervi phrenici is a long and slender branch which accom- 

 panies the phrenic nerve. 



The mediastinal and pericardiac branches are small vessels distri- 

 buted to the anterior mediastinum, the thymus gland, and peri- 

 cardium. 



The Musculo-phrenic artery winds along the attachment of the 

 diaphragm to the ribs, supplying that muscle and sending branches to 

 the inferior intercostal spaces. " The mammary arteries," says Dr. 

 Harrison, "are remarkable for the number of their inosculations, and 

 for the distant parts of the arterial system which they serve to con- 

 nect. They anastomose with each other, and their inosculations, with 

 the thoracic aorta, encircle the thorax. On the parietes of this cavity 

 their branches connect the axillary and subclavian arteries ; on the 

 diaphragm they form a link in the chain of inosculations between the 

 subclavian artery and abdominal aorta, and in the parietes of the ab- 

 domen they form an anastomosis most remarkable for the distance be- 



