I096 A MANUAL OF ANATOMY 



from the cephalic vein. Posterior. — The scalenus medius, with 

 the close intervention of the lower nerve-trunk of the brachial 

 plexus. Superior. — 'The upper and middle nerve-trunks of the 

 brachial plexus, the latter being nearest the vessel. Inferior. — 

 The upper surface of the first rib and the subclavian vein, the vein 

 being on a more anterior plane than the artery, and lying behind the 

 clavicle. 



The third part of the subclavian artery does not usually furnish 

 any branch. In some cases, however, the posterior scapular artery 

 arises from it, instead of from the transverse cervical branch of the 

 thyroid axis from the first part of the subclavian. In these cases 

 the posterior scapular artery passes outwards between the nerve- 

 trunks of the brachial plexus. 



The direction of the third part of the artery is indicated by a line 

 drawn from a point on the posterior border of the sterno-cleido- 

 mastoid muscle, about \ inch above the clavicle, to the centre of 

 that bone. The artery is accessible to compression as it passes 

 over the first rib, the guide to it at this point being the centre of the 

 clavicle. In ligation of the artery the guide to it is the scalene 

 tubercle or spine (tubercle of Lisfranc) on the inner border of the 

 first rib, behind which tubercle the vessel lies ; and the scalenus 

 anticus muscle, which is usually covered by the clavicular part of 

 the sterno-cleido-mastoid, le'ads to this tubercle. 



For the manner in which the collateral circulation is carried on 

 after ligation of the third part of the subclavian artery, see p. 324. 



The subclavian vein, in the region of the subclavian triangle, is 

 situated behind the clavicle, where it lies below and anterior to 

 the artery. On the upper surface of the first rib it is anterior to 

 the scalenus anticus, and it receives the external jugular vein, 

 and in some cases the anterior jugular vein. 



The transverse cervical artery lies in the subclavian triangle for 

 a short distance only, close to where the posterior belly of the omo- 

 hyoid passes beneath the sterno-cleido-mastoid. It passes outwards 

 beneath the former muscle into the lower part of the occipital 

 triangle, where it divides into its superficial cervical and posterior 

 scapular branches, the former entering the trapezius, and the latter 

 passing beneath the levator anguli scapulae, after which it descends 

 along the base of the scapula, under cover of the rhomboid muscles. 



The transverse cervical vein opens into the external jugular vein, 

 there being a valve at, or near, its ending. 



The suprascapular artery is not in the subclavian triangle, but lies 

 behind the clavicle, close to its upper aspect. It will be described in 

 connection with the first part of the subclavian artery (see p. 1143). 



The suprascapular vein also lies behind the clavicle, and it opens 

 into the external jugular vein, there being a valve at, or near, its 

 ending. 



The external jugular vein will be found described on p. 1084. 



Brachial Plexus. — ^The brachial plexus is situated in the lower 

 part of the posterior triangle of the neck, behind the clavicle, and 

 in the upper part of the axilla. Its complex formation is rendered 



