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780 THE VASCULAR SYSTEM. 
anastomose with branches of the suprascapular and subscapular arteries. It also sends 
branches backwards through and between the rhomboid muscles, which anastomose with 
the superficial cervical artery and with the dorsal branches of the intercostal arteries. 
(C) The suprascapular artery (a. transversa scapule) springs from the thyroid 
axis, and terminates in the infraspinous fossa of the scapula. As a rule it is 
smaller than the transverse cervical artery. 
Commencing behind the internal jugular vein, it crosses the scalenus anticus 
and phrenic nerve, and is covered in front by the sterno-mastoid and the anterior 
jugular vein; on the left side it lies behind the termination of the thoracic 
duct also. Continuing outwards and backwards behind the clavicle, and crossing 
superficially to the third part of the subclavian artery and the cords of the brachial 
plexus, it reaches the suprascapular notch and passes over the suprascapular liga- 
ment. From this point it descends with the suprascapular nerve through the 
supraspinous fossa and beneath the supraspinatus muscle, and passing through 
the great scapular notch under the spino-glenoid ligament, enters the infraspinous 
fossa, where it anastomoses with the dorsal branch of the subscapular and with 
branches of the posterior scapular arteries. 
Branches.—(«) Muscular, to the sterno-mastoid, the subclavius, and the muscles on 
the dorsum of the scapula. 
(0) The medullary, a small branch to the clavicle. 
(c) The suprasternal, to the sternal end of the clavicle and the sterno-clavicular 
joint. 
(@) Acromial branches, which ramify over the acromion process, anastomosing with 
the acromial branches of the acromio-thoracic and the posterior circumflex arteries. 
(ce) Articular, to the acromio-clavicular and shoulder joints. 
(f) The subscapular, which is given off as the artery, passes over the transverse supra- 
scapular ligament. It passes down into the subscapular fossa, gives branches to the 
subscapularis, and anastomoses with the branches of the subscapular and posterior 
scapular arteries. 
(y) Supraspinous, which ramify in the supraspinous fossa, supplying the muscle, and 
anastomosing with the posterior scapular. 
(h) Terminal branches ramify in the infraspinous fossa, and anastomose with the 
dorsalis scapulee and with branches of the posterior scapular artery. 
(3) Internal Mammary Artery (a. mammaria interna, Fig. 552).—This arises 
from the lower and front part of the subclavian at the inner border of the scalenus 
anticus and immediately below the origin of the thyroid axis. It terminates 
behind the inner extremity of the sixth intercostal space by dividing into the 
musculo-phrenic and the superior epigastric arteries. 
The artery passes at first downwards, forwards, and inwards, lying upon the 
pleura, and behind the subclavian vein, the sternal end of the clavicle, and the 
cartilage of the first rib: it is crossed obliquely from without inwards by the 
phrenic nerve, which usually passes in front of it. From the cartilage of the first 
rib it descends vertically, about half-an-inch from the border of the sternum, and 
lies in the upper part of its course upon the pleura, and in the lower part upon the 
triangularis sterni. It is covered in front by the cartilages of the upper six ribs, 
the intervening intercostal muscles, and the terminal portions of the intercostal 
nerves, and it is accompanied by two vena comites, which unite together above and 
on its inner side to form a single trunk which terminates in the innominate vein. 
Branches.—(a) The comes nervi phrenici (a. pericardiaco-phrenica), or superior 
phrenic artery, is a long slender branch which is given off from the upper part of theg 
internal mammary. It accompanies the phrenic nerve through the superior and middle 
mediastinal spaces to the diaphragm, where it anastomoses with the inferior phrenic and 
musculo-phrenic arteries. In its course downwards the artery gives off numerous small 
branches to the pleura and pericardium, which anastomose with offsets of the mediastinal 
and pericardial branches of the aorta and internal mammary arteries, and also with the 
bronchial arteries, forming the wide-meshed subpleural plexus of ‘Turner. 
(6) Mediastinal branches (aa. mediastinales anteriores), small and numerous, pass to 
the areolar tissue of the anterior mediastinal space and supply the remains of the thymus 
gland and the sternum. 
a 
