THORACIC WALL 9 



Arteria Mammaria Interna. This vessel arises, in the root 

 of the neck, from the first part of the subclavian. It enters 

 the thorax by passing downwards, posterior to the sternal end 

 of the clavicle and the cartilage of the first rib, and it descends 

 to the interval between the sixth and seventh costal cartilages, 

 where it ends by dividing into the superior epigastric and the 

 musculo-phrenic branches. 



Placed anterior to the internal mammary artery are the 

 upper six costal cartilages, with the intervening internal inter- 

 costal muscles and anterior intercostal membranes. The inter- 

 costal nerves cross anterior to it before they turn forwards to 

 gain the surface. Posterior to the upper part of the artery is 

 the pleura ; and the transversus thoracis intervenes between 

 the lower part of the artery and the pleural sac. 



In addition to its two terminal branches, a large number 

 of small collateral twigs proceed from the internal mammary 



to < he thoradc 



\. :} '<> P* ** -'ior of the thorax. 



I'. . i } *e terminal branches. 



The anterior intercostal arteries are supplied to the upper six 

 intercostal intervals, and have been dissected already (p. 6). 

 Two are given to each space : frequently these arise by a 

 common trunk. 



The perforating arteries accompany the anterior cutaneous 

 nerves, and reach the surface by piercing the internal inter- 

 costal muscles, the anterior intercostal membranes, and the 

 pectoralis major muscle. One, or perhaps two, are given 

 off in each intercostal space. In the female those of the 

 second, third, and fourth spaces attain a special importance, 

 inasmuch as they constitute the principal arteries of supply to 

 the mammary gland. 



The superior epigastric artery passes between the sternal and 

 costal origins of the diaphragm and enters the sheath of the 

 rectus muscle of the abdominal wall. 



The musculo-phrenic artery turns laterally and downwards, 

 along the costal origin of the diaphragm and behind the rib- 

 cartilages. Opposite the eighth costal cartilage it pierces the 

 diaphragm and terminates on its abdominal surface. It gives 

 off the anterior intercostal arteries to the seventh, eighth, and 

 ninth intercostal spaces (p. 7). 



