THE SUBCLAVIAN ARTERIES. Oe 
The first parts of the subclavian arteries differ materially from each other both in 
extent and relations. The relations of the second and third parts are similar on 
both sides. 
The first part of the left subclavian artery springs from the arch of the 
aorta to the left of and behind the commencement of the left common carotid and 
on the left side of the trachea. It ascends, almost vertically, in the superior 
mediastinum to the root of the neck, where it arches upwards and outwards to the 
inner border of the scalenus anticus. 
Relations.— Posterior.—In the superior mediastinum, from below upwards, it is in 
relation behind and with the left margin of the cesophagus, the thoracic duct, and the left 
longus colli muscle. 
“Anterior—In front and to the right of the artery are the vagus, the left superior 
vardiac branch of the sympathetic, the left inferior cardiac branch of the vagus, the left 
phrenic nerve, and the left common carotid artery. It is also crossed obliquely by the 
left Immominate vein above and by the left vagus nerve below, and it is overlapped on 
the left side by the left lung and pleura. 
Lateral.—Internally it is in relation, from below upwards, with the trachea, the left 
recurrent laryngeal nerve, the oesophagus, and the thoracic duct. 
Externally it is closely invested by the left pleura, and it ascends in a groove on the 
inner aspect of the left lung. 
As it turns outwards at the root of the neck it lies behind the terminations of the 
internal jugular, vertebral, and subclavian veins, the phrenic nerve, the sterno-thyroid and 
sterno-hyoid muscles, the anterior jugular vein, and more superficially the sterno-mastoid 
“muscle, and the deep cervical fascia; the thoracic duct arches obliquely over it, and it 
lies in front of the apex of the pleural sac. 
The first part of the right subclavian artery (Fig. 552) extends from the 
back of the right sterno-clavicular articulation to the inner border of the scalenus 
anticus. It is thus limited to the root of the neck. 
Relations.— Postervor.—Behind this part of the artery, and intervening between it 
and the upper two dorsal vertebree, are the recurrent laryngeal nerve, the posterior part 
of the annulus Vieusseni, and the apex of the right pleural sac. Anterior.—In front it is 
in relation with the right vagus, the cardiac branches of the vagus and the sympathetic, 
the anterior portion of the annulus Vieusseni, the internal jugular and vertebral veins, 
and more superficially the sterno-hyoid and sterno-thyroid muscles, the anterior jugular 
vein, the sternal end of the clavicle, the sterno-clavicular ligaments, and the sterno- 
mastoid muscle. The recurrent laryngeal nerve passes below it and intervenes between it 
and the apex of the pleural sac. 
The second part of the subclavian artery, on each side, extends from the 
inner to the outer border of the scalenus anticus, behind which it lies. 
Relations.—A4ehind and Jelow it is in relation with the pleural sac. In front it is 
covered by the anterior scalene and the sterno-mastoid muscles. The anterior scalene 
separates it from the subclavian vein, which also lies at a slightly lower level, from the 
transverse cervical and suprascapular arteries, from the anterior jugular vein, and, on the 
right side, from the phrenic nerve. 
The third part of the subclavian artery is the most superficial portion. 
It extends from the outer border of the anterior scalene to the outer border of 
the first rib, lying partly in the clavicular portion of the posterior triangle and 
partly behind the clavicle and the subclayius muscle. 
Relations.—It rests upon the upper surface of the first rib. Immediately behind it 
is the lowest trunk of the brachial plexus, which separates it from the middle scalene. 
In front of it and at a slightly lower level lies the subclavian vein. The external 
jugular vein crosses the inner part of this portion of the artery in its course to the sub- 
clavian vein, and just before its termination receives the transverse cervical and supra- 
scapular veins ; these vessels also pass superficial to the artery, which is thus covered by 
venous trunks ; it is also crossed vertically, behind the veins, by the nerve to the subclavius 
muscle. The outer section of this part of the artery lies behind the clavicle and the 
subclavius muscle, and it is crossed from within outwards by the suprascapular artery, 
