POSITION OF THE SUBCLAVIAN VESSELS. 577 



ues from beneath the anterior scalenus muscle, and is directed 

 over the first rib to the axilla. In the ordinary condition of the 

 vessel the companion subclavian vein is seldom seen, owing to its 

 being placed lower down behind the clavicle. Above the artery and their 

 are the large cords of the brachial plexus ( 9 ), which accompany the 

 I, and become closely applied to it beneath the clavicle. 

 Behind the artery and the nerves is the middle scalenus muscle ( 5 ). 

 And below the vessel is the first rib. 



Along the lower boundary of the space, and rather beneath the Branches 

 clavicle, lie the suprascapular vessels ; and crossing the upper angle, of vessels - 

 at the meeting of the omo-hyoid and sterno-mastoid muscles, are 

 the transverse cervical vessels. Entering the space from above is the 

 external jugular vein ( 8 ), which descends over (seldom under) 

 the omo-hyoid, and opens into the subclavian vein ; in this region 

 the vein receives the suprascapular and transverse cervical branches, 

 and sometimes a small vein over the clavicle, from the cephalic 

 vein of the arm. 



The length of this space depends mainly upon the extent of the Variations 

 attachment of the trapezius and sterno-mastoid muscles to the of the space, 

 clavicle : in some bodies these muscles occupy nearly the whole 

 length of that bone, leaving but a small interval between them ; 

 find occasionally they meet, so as to cover the subclavian artery 

 altogether. The space also varies in height according to the 

 position of the omo-hyoid, for this muscle sometimes lies close to, 

 :)r even arises from the clavicle, while on the other hand, it may be 

 listant one inch and a half from that bone. 



In depth the space varies naturally ; and in a short thick neck also in the 

 with a prominent clavicle, the artery is farther from the surface 

 than in the opposite condition of the parts. But the depth may be 

 altered much more by change in the position of the clavicle, as the 

 shoulder is carried forwards or backwards. And lastly, the artery and 

 may be concealed entirely in its usual position by forcing upwards artificial - 

 the arm and shoulder, as the collar-bone can be raised above the 

 level of the omo-hyoid muscle. 



The position of the subclavian artery itself is also subject to Departure 

 variation, for the vessel may be one inch and a half above the ordinary 

 clavicle, or at any point intermediate between this and the bone; state of the 

 therefore the drawing down of the shoulder, so as to expose the &nd .^ 

 vessel as much as possible, is an important preliminary in opera- branches, 

 tions to reach the subclavian artery in this space. In the typical 

 condition there is not any branch arising from the trunk in this 

 part of its course ; but the posterior scapular artery (fig. 210) is 

 frequently given off beyond the scalenus anticus, and sometimes 

 there is more than one branch. 



The subclavian vein occasionally rises upwards as high as the Position of 

 artery ; or in some rare instances, it even lies with the artery v< 

 beneath the anterior scalenus. The position of the external 

 jugular vein with regard to the subclavian artery is very uncertain ; 

 and the branches connected with its lower end often form a kind of 

 plexus over the arterial trunk. 



D.A. P p 



