PRACTICAL CONSIDERATIONS: SUBCLAVIAN ARTERY. 757 



inate at an acute angle with the carotid and deeper by the full diameter of the 

 latter. The needle should be passed from below upward, while the pleura is gently- 

 depressed with the finger. 



The second portion — behind the scalenus anticus — has in a few cases been suc- 

 cessfully ligated for aneurism external to it, but the operation does not require 

 special description. It is identical with that for tying the third portion, with the 

 addition of more extensive division of the clavicular portion of the sterno-mastoid 

 and a partial division of the scalenus anticus, having due regard to the position of 

 the phrenic nerve on the inner part of the anterior surface of that muscle. 



The third portion — from the outer edge of the scalenus anticus to the lower 

 border of the first rib — has been frequently and successfully ligated. Three methods 

 may be described : 



1. By the first and usual one it is approached by a transverse incision, parallel 

 with the clavicle and extending along the base of the posterior cervical triangle from 

 the middle of the clavicular head of the sterno-mastoid to the anterior border of the 

 trapezius. This is best made by drawing the skin down and incising it directly 

 upon the bone, in this way easily avoiding the external jugular vein. The platysma 

 muscle and the supraclavicular nerves are divided at the same time. On releasing the 

 skin the wound will be placed about a half-inch above the clavicle. The shoulder is 

 then well depressed so as to lower this bone and increase the supraclavicular space. 

 The deep fascia, which, as it is attached to the superior border of the clavicle, is not 

 pulled down with the skin and platysma, is then divided, the external jugular vein 

 drawn aside or tied and cut, the loose cellular tissue, and possibly the omo-hyoid 

 aponeurosis, scratched through or cut, and one or the other of four landmarks iden- 

 tified : (^) the tense outer edge of the anterior scalene muscle or (^) the scalene 

 tubercle at the insertion of that muscle into the first rib, the artery lying just 

 outside these on the rib; (f) the first rib itself traced inward with the finger from the 

 outer angle of the wound until the artery is reached ; (^) the lowest cord of the 

 brachial plexus, lying immediately above, or sometimes slightly overlapping the artery. 

 The cord has been mistaken for the vessel, but compression between the finger and 

 the rib does not flatten it out, as in the case of the artery, and, of course, does not 

 arrest the radial pulse. The tubercle is often poorly developed, and has a less close 

 relation to the vessel when the latter rises high above the clavicle. The process of 

 cervical fascia reaching from the posterior border of the scalenus to the sheath of the 

 artery may be so tense as to obscure to both sight and touch the line of the outer 

 edge of the muscle 



The artery is cautiously denuded, care being taken to avoid injury to the 

 pleura or to the subclavian vein. The transverse cer\-ical artery is usually above 

 and the suprascapular artery below the line of incision. The phrenic nerve has 

 been known to pass directly over the third portion of the subclavian (Agnew), 

 and the possibility of the presence of this rare anomaly should be remembered. 

 The needle, the tip kept between the artery and the rib, is passed from above down- 

 ward, and from behind forward and a little inward. In the case of a high arch of the 

 subclavian the third portion is nearly vertical, and it would then be more correct to 

 speak of passing the needle from without inward. 



2. The middle of the clavicle for two or more inches, or the whole clavicle, may 

 be resected subperiosteally, as in interscapulo-thoracic amputations, and the ap- 

 proach to the artery greatly facilitated. 



3. By strongly elevating — instead of depressing — the shoulder and clavicle, 

 using the arm as a tractor, the artery may be exposed by an incision just belotv and 

 parallel with the middle of the clavicle. A portion of the outer edge of the pec- 

 toralis major and some of the inner deltoid fibres will usually have to be divided, 

 although it may be possible to gain sufficient room by drawing the margin of the 

 former muscle inward and that of the latter outward. The cephalic vein dipping in 

 through this intermuscular depression (Mohrenheim's fossa) to join the axillary 

 vein must be avoided. The artery is found lying between the vein internally and 

 the close bundle of the cords of the brachial plexus externally. The point at which 

 the vessel is tied is said to be identical with that at which it is ligated through the 

 usual incision (Dawbarn). 



