THORACIC WALL 15 



between the sixth and seventh costal cartilages, where it ends 

 by dividing into the superior epigastric and the musculo-phrenic 

 branches (Figs. 4, 27). 



Placed anterior to the internal mammary artery are the 

 upper six costal cartilages, \vith 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. 



The branches of the internal mammary artery are two 

 terminal and a large number of small collateral twigs 



c 5ta1 ' : ) to lhe thorack 



r;'. ) P-* * ^ interior of the thorax. 



:} 



">< 



The a/itetior intercostal arteries are supplied to the upper six 

 intercostal intervals, and have been dissected already (p. 12). 

 Two are given to each space : each pair may arise by a 

 common trunk from the internal mammary stem. 



The perforating arteries accompany the anterior cutaneous 

 nerves. They 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 are important 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. 



Vena Mammaria Interna. Each internal mammary artery 

 is accompanied in the greater part of its course by two venae 

 comites. At the upper part of the thor. < the venae comites 



