THE SUBCLAVIAN ARTERIES. 517 



PLAN or RELATIONS OF SECOND PORTION OF SUBCLAVIAN ARTERY. 



In front. 



Skin and superficial fascia. 

 Platysma and deep cervical fascia. 

 Sterno-mastoid. 

 Phrenic nerve. 

 Scalenus anticus. 

 Subclavian vein. 



Above. I Subclavian \ Below. 



. Artery. 



Brachial plexus. I e rt ? n n d ) Pleura. 



Behind. 

 Pleura and Middle Scalenus. 



The Third Portion of the Subclavian Artery passes downward and outward 

 from the outer margin of the Scalenus anticus to the outer border of the first rib, 

 where it becomes the axillary artery. This portion of the vessel is the most 

 superficial, and is contained in a subclavian triangle (see page 502). 



Relations. It is covered, in front, by the skin, the superficial fascia, the 

 Platysma, the descending clavicular branches of the cervical plexus, and the deep 

 cervical fascia ; by the clavicle, the Subclavius muscle, and the suprascapular 

 artery and vein, and the transverse cervical vein ; the nerve to the Subclavius 

 muscle passes vertically downward in front of the artery. The external jugular 

 vein crosses it at its inner side, and receives the suprascapular and transverse 

 cervical veins, which frequently form a plexus in front of it. The subclavian 

 vien is below and in front of the artery, lying close behind the clavicle. Behind, 

 it lies on the Middle scalene muscle and the lowest cord of the brachial plexus, 

 formed by the union of the last cervical and first dorsal nerves. Above it, and 

 to its outer side, is the brachial plexus and Omo-hyoid muscle. Below, it rests on 

 the upper surface of the first rib. 



PLAN OF RELATIONS OF THIRD PORTION OF SUBCLAVIAN ARTERY. 



In front. 



Skin and superficial fascia. 

 Platysma and deep cervical fascia. 



Descending branches of cervical plexus. Nerve to Subclavius muscle. 

 Subclavius muscle, suprascapular artery, and vein. 

 The external jugular and transverse cervical veins. 

 The clavicle. 



Brachial plexus. \ sSSS,. j First rib. 



Omo-hyoid. 



Behind. 



Scalenus medius. 



Lower cord of brachial plexus. 



Peculiarities. The subclavian arteries vary in their origin, their course, and the height to 

 which they rise in the neck. 



The origin of the right subclavian from the innominate takes place, in some cases, above the 

 sterno-clavicular articulation, and occasionally, but less frequently, in the cavity of the thorax, 

 below that joint. Or the artery may arise as a separate trunk from the arch of the aorta. In 

 such cases it may be either the first, second, third, or even the last branch derived from that ves- 

 sel ; in the majority of cases it is the first or last, rarely the second or third. When it is the first 

 branch, it occupies the ordinary position of the innominate artery ; when the second or third, it 

 gains its usual position by passing behind the right carotid ; and when the last branch, it arises 

 from the left extremity of the arch, at its upper or back part, and passes obliquely toward the 



