THE INTERNAL MAMMARY ARTERY. 



427 



Varieties. The transverse cervical branch of the thyroid axis not unfrequently consists 

 solely of the superficial cervical artery ; and it often happens that the vessel derived from 

 the thyroid axis is very small, and represents only in part the superficial cervical artery, a 

 large vessel being 1 given off from the second or third part of the subclavian and dividing 

 near the levator anguli scapulae into two branches, of which one ascends and represents 



Fig. 354. DISSECTION OF THE ANTERIOR THORACIC AND 



ABDOMINAL WALL, TO SHOW THE ANASTOMOSES OP 

 THE INTERNAL MAMMARY, INTERCOSTAL, AND EPI- 

 GASTRIC ARTERIES. (Allen Thomson, after Tiede- 

 mann. ) 5 



The fore part of the serratus magnus, the external 

 and internal oblique, and the rectus abdominis muscles 

 have been removed. 1, upon the subclavius muscle, 

 points to the first part of the axillary artery, giving 

 rise to the acromio-thoracic artery, which is cut short ; 

 2, upon the pectoralis minor, points to the lower part 

 of the axillary artery and vein ; 3, long thoracic artery ; 

 4, on the cartilage of the first rib, the upper part of 

 the internal mammary artery ; 4', the lower part of the 

 same artery, giving its abdominal branch behind the 

 cartilage of the seventh rib ; 5, in the fourth intercostal 

 space, the anastomosis of the internal mammary and 

 intercostal arteries ; 6, perforating branches of the in- 

 ternal mammary artery sending offsets over the front of 

 the sternum ; 7, on the transversalis muscle immediately 

 above the internal abdominal ring, points to the last 

 part of the external iliac artery, from which are seen 

 arising, 8, the deep epigastric artery, and 9, the deep 

 circumflex iliac ; 10, the anastomosis of the epigastric 

 with the abdominal branch of the internal mammary 

 artery ; 11, spermatic cord and cremasteric twig of the 

 epigastric artery ; 12, femoral artery ; 13, femoral vein ; 

 14, a lymphatic gland in the femoral ring. 



the larger portion of the superficial cervical artery, 

 while the other forms the posterior scapular. 



The transverse cervical artery is sometimes de- 

 rived directly from the subclavian, beneath or even 

 beyond the scalenus anticus muscle. The transverse 

 or superficial cervical sometimes gives off the as- 

 cending cervical artery. 



When the superjiclal cervical is separated from 

 the posterior scapular, it sometimes arises from 

 other sources than the thyroid axis, as from the 

 suprascapular or the subclavian artery. 



3. Internal mammary artery (iv). 

 The internal mammary artery, remarkable for 

 its length and the number of its branches, 

 arises from the lower and fore part of the 

 subclavian, opposite the thyroid axis. It 

 runs at first forwards and downwards, as well 

 as slightly inwards, to the hinder surface of 

 the cartilage of the first rib, lying between 

 this and the sac of the pleura ; from this point it descends vertically behind 

 the costal cartilages, about half an inch from the border of the sternum, as 

 far as the interval between the sixth and seventh cartilages, where it ends 

 by dividing into two branches, which are known as the musculo-phrenic and 

 superior epigastric arteries. The internal mammary artery is covered at its origin 

 by the subclavian vein ; and as it passes forwards it arches round the upper end of 

 the innominate vein, and is crossed from without inwards by the phrenic nerve. In 

 the chest it has the costal cartilages and the internal intercostal muscles, as well as the 



