THE SUBCLAVIAJST ARTEKIES. 909 



ARTERIES OF THE UPPER EXTREMITY. 



The main arterial stem of each upper extremity passes through the root of the 

 ineck, traverses the axillary space, and is continued through the arm to the 

 forearm. In the forearm its extent is short, for it terminates, opposite the neck 

 )f the radius, by bifurcating into the radial and ulnar arteries, which run through 

 the forearm to the hand. That portion of the common trunk which lies in the 

 root of the neck is known as the subclavian artery, the part in the axillary space 

 is termed the axillary artery, whilst the remaining part is called the brachial artery. 





ARTERIvE SUBCLAVI.E. 



On the right side the subclavian artery (Figs. 757, 759, 761, and 766) 

 iommences at the termination of the innominate artery, posterior to the sterno- 

 3lavicular articulation, whilst that on the left side arises from the arch of the 

 lorta, behind the upper half of the manubrium sterni. 



The right artery is about 75 mm. (3 inches) long ; it lies in the root of the 

 leek. The left artery is about 100 mm. (4 inches) long, and is situated not only 

 .n the root of the neck, but also in the superior mediastinal part of the thorax, 

 [n the root of the neck each artery arches laterally, across the apex of the lung and 

 Behind the anterior scalene muscle, and is divided into three parts, which lie 

 respectively to the medial side, behind, and to the lateral side of the muscle. 

 The extent to which the arch rises above the level of the clavicle varies ; not un- 

 commonly it reaches the level of the lower part of the thyreoid gland. The first parts 

 )f the subclavian arteries differ materially from each other both in extent and re- 

 ations. The relations of the second and third parts are similar on the two sides. 



The first part of the left subclavian artery springs from the arch of the 

 iorta, posterior to the commencement of the left common carotid and on the left 

 tide of the trachea. It ascends almost vertically, in the superior mediastinum, to 

 ;he root of the neck, where it arches upwards and laterally to the medial border 

 )f the scalenus anterior muscle. 



Relations. Posterior. In the superior mediastinum it is in relation with the lung 

 ind pleura. 



Anterior. In front are the left vagus, the left superior cardiac branch of the 

 sympathetic, the left inferior cardiac branch of the vagus, the left phrenic nerve, and the 

 eft common carotid artery. It is also crossed obliquely by the left vagus nerve, and it is 

 1 Dverlapped on the left side by the left lung and pleura. 



Medial. Medially it is in relation, from below upwards, with the trachea, the left 

 -ecurrent nerve, the oesophagus, and the thoracic duct, the latter lying in a plane posterior 

 :o the oesophagus and the artery. 



Laterally it is closely invested by the left pleura, and it ascends in a groove on the 

 nedial aspect of the left lung. 



At the root of the neck, as it turns laterally, it lies behind the commencement of the 

 left innominate vein, and the termination of the left vertebral vein, the phrenic nerve, the 

 iterno-thyreoid 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 

 5ver it ; and it lies in front of the apex of the pleural sac and lung. 



The first part of the right subclavian artery (Fig. 761) extends from the 

 ' back of the right sterno-clavicular articulation to the medial border of the scalenus 

 interior. It is thus limited to the root of the neck. 



Relations. Posterior. Behind this part of the artery, and intervening between it 

 and the upper two thoracic vertebrae, are the recurrent nerve, the posterior part of the 

 insa subclavia, and the apex of the right pleural sac. Anterior. In front it is in relation 

 ith the right vagus, the cardiac branches of the vagus and the sympathetic, the anterior 

 ;ion of the ansa subclavia, the internal jugular and vertebral veins, and more super- 

 cially the sterno-hyoid and sterno-thyreoid muscles, the anterior jugular vein, the sternal 

 i of the clavicle, the sterno-clavicular ligaments, and the sterno-mastoid muscle. The 

 urrent nerve passes below it and intervenes between it and the apex of the pleural sac. 





