INTERNAL MAMMARY 



399 



The posterior scaprdar, the continuation of the transversalis colli, passes beneath 

 the Levator anguli scapulae to the superior angle of the scapula, and descends 

 along the posterior border of that bone as far as the inferior angle, where it anas- 

 tomoses with the subscapular branch of the axillary. In its course it is covered 



Fig. 216. The Scapular and Circumflex Arteries. 



Ettttricr Sra/niiir 



Sulttaflular . 



by the Ehomboid muscles, supplying these, the Latissimus dorsi and Trapezius, 

 and anastomosing with the suprascapular and subscapular arteries, and with the 

 posterior branches of some of the intercostal arteries. 



Peculiarities. The superficial cervical frequently arises as a separate branch from the thyroid 

 axis ; and the posterior scapular from the third, more rarely from the second, part of the sub- 

 clavian. 



The INTERNAL MAMMARY arises from the under surface of the first portion of 

 the subclavian artery, opposite the thyroid axis. It descends behind the clavicle, 

 to the inner surface of the anterior wall of the chest, resting upon the costal 

 cartilages, a short distance from the margin of the sternum ; and, at the interval 

 between the sixth and seventh cartilages, divides into two branches, the musculo- 

 phrenic, and superior epigastric. 



At its origin, it is covered by the internal jugular and subclavian veins, and 

 crossed by the phrenic nerve. In the upper part of the thorax, it lies upon the 

 costal cartilages, and Internal intercostal muscles in front, covered by the pleura 

 behind. At the lower part of the thorax, the Triangularis sterni separates this 

 vessel from the pleura. It is accompanied by two veins, which join at the upper 

 part of the thorax into a single trunk. 



The branches of the internal mammary are the 



Comes nervi phrenici or Superior phrenic. 



Mediastinal. 



Pericardiac. 



Sternal. 



Anterior intercostal. 

 Perforating. 

 Musculo-phrenic. 

 Superior epigastric. 



The comes nervi phrenici or superior phrenic is a long slender branch, which 

 accompanies the phrenic nerve, between the pleura and pericardium, to the Dia- 

 phragm, to which it is distributed ; anastomosing with the other phrenic arteries 

 from the internal mammary, and abdominal aorta. 



