51 G THE ARTERIES 



(1) The posterior scapular — the a})paveiit continuation of the transverse 

 cervical artery — begins at the outer border of the levator anguU scapuUe, and, 

 continuing its course beneath this muscle to the U])per and posterior angle of the 

 scapula, turns downwards and skirts along the ])osterior border of the scapula, 

 between the serratus niagnus in front and the levator anguli scapula; and rhom- 

 boideus minor and major behind, to the inferior angle, where it anastomoses ^yith 

 the subscapular artery. It gives off the folloAving branches: — (a) Supraspinous, 

 which ramifies lietween the supraspinous muscle and the trapezius, and sends 

 branches through the muscle into the fossa, to anastomose Avith the suprascapular 

 arter}'. (6) Infraspinous branches, one or more of which enter the infraspinous 

 fossa, and anastomose with the dorsal scapular, {c) Subscapular branches, 

 which enter the subscapular fossa, and anastomose Avith the suprascapular, infra- 

 scapular, and subscapular arteries, {d) Muscular branches, to the muscles 

 between Avhich it runs and to the latissimus dorsi. These branches anastomose with 

 the posterior divisions of the intercostal arteries. 



(2) The superficial cervical artery, smaller than the posterior scapular, 

 ascends under cover of the anterior margin of the trajjezius, lying upon the levator 

 anguli scapulae and splenius muscles. It supplies branches to the trapezius, levator 

 anguli scapulffi, and splenius muscles, and the posterior chain of lymphatic glands. 

 It anastomoses with the superficial branch of the princeps cervicis Avhich descends 

 from the occipital betAveen the splenius and complexus. It is accompanied by two 

 veins. This artery may arise directly from the thyroid axis, or from the third 

 l)art of the subclavian artery. 



THE INTERNAL MAMMARY ARTERY 



The internal mammary artery (fig. 344) comes off from the loAver part of the 

 first 2)ortion of the subclavian, usually opposite the thyroid axis, close to the inner 

 edge of the scalenus anticus, occasionally opposite the vertebral, or at a spot 

 l)etAveen these tAVO vessels. It descends Avith a slight inclination forwards and 

 iuAvards, under cover of the clavicle, and enters the thorax behind the cartilage of 

 the first rib, and thence passes doAvn behind the cartilages of the next succeeding 

 ribs, about half an inch from the external margin of the sternum, to the sixth 

 interspace, Avhere it divides into the superior epigastric and musculo-phrenic. 

 It is accompanied by two veins, Avhich unite into one trunk behind the first 

 intercostal muscle, and pass to the inner side of the artery into the corresponding 

 vena innominata; occasionally on the right side into the vena cava superior direct. 

 The artery may l;)e divided into tAvo portions, the cervical and the thoracic. 



The cervical portion is covered by the sterno-mastoid muscle, subclavian vein, 

 and internal jugular vein, and is crossed obliquely, from Avithout iuAvards, by the 

 phrenic nerve. It rests upon the pleura and courses round the upper part of the 

 innominate vein. There is no branch from this part of the artery. 



The thoracic portion lies behind the cartilages of the six upper ribs, and in 

 the interspace betAveen the ribs has in front of it the pectoralis major and the 

 internal intercostal muscles and the external intercostal membrane. Behind, it is- 

 in contact above Avith the pleura, but it is separated from it loAver doAvn by slips 

 of the triangularis sterni. On the left side the artery Ix'tAveen the fourth and sixth 

 ribs maybe said to be in the anterior mediastinum, the pleura here forming a notch 

 for the heart, '[w the first, second, and third spaces the artery, if Avounded, can 

 be easily tied; but in the fourth space the operation is attended Avith more difficulty. 

 The remaining spaces are so narroAV that a portion of the cartilage Avould have to 

 be removed to ex])Ose the A'cssel. 



The branches of the internal mammary artery are: — (1) The superior 

 phrenic; (^2 j the mediastinal, or thymic; (o) the ])ericardiac; (4) the sternal; (5) 

 the anterior intercostals; (6) the perforating; (7) the lateral infracostal; (8) tlie 

 superior epigastric; and (9) the nuisculo-phrenic. 



(1) The superior phrenic, or comes nervi phrenici, is a long slender vessel 

 Avhich comes off from the internal mammary just after it has entered tlie chest, and 

 descends Avith the phrenic nerve, at first betAveen the i)leura and innominate vein; 



